WO2014203179A2

WO2014203179A2 - Ceria-zirconia-mixed oxide particles and process for their production by pyrolysis of dispersions

Info

Publication number: WO2014203179A2
Application number: PCT/IB2014/062364
Authority: WO
Inventors: Rene König; Stefan Hannemann; Wieland Koban; Mirko Arnold; Andreas Sundermann; Bernd Sachweh; Kerstin FRANK; Caroline Mages-Sauter; Stefan Kotrel
Original assignee: Basf Se; Basf (China) Company Limited
Priority date: 2013-06-18
Filing date: 2014-06-18
Publication date: 2014-12-24
Also published as: WO2014203179A3

Abstract

The present invention relates to a process for the production of mixed oxide particles comprising: (1) providing a dispersion comprising a disperse phase and a continuous phase, wherein the disperse phase comprises one or more precursor compounds of ceria, one or more precursor compounds of zirconia, and one or more precursor compounds of one or more rare earth oxides other than ceria and/or one or more precursor compounds of yttria; (2) forming an aerosol of the dispersion provided in step (1); and (3) pyrolyzing the aerosol of step (2) to obtain mixed oxide particles, as well as to mixed oxide particles obtainable from flame spray pyrolysis, and preferably obtain- able by the inventive process and to its use.

Description

Ceria-Zirconia-Mixed Oxide Particles and Process for their Production by Pyrolysis of Dispersions

The present invention relates to a process for the production of mixed oxide particles comprising ceria and zirconia as well as to mixed oxide particles obtainable from the inventive process and in particular from flame spray pyrolysis of precursor containing dispersions. Furthermore, the present invention relates to mixed oxide particles as such which may be obtained according to the inventive process as well as to the use of mixed oxide particles and in particular of those obtainable according to the inventive process.

INTRODUCTION

In the field of exhaust gas treatment and in particular in methods for the combustive or oxidative treatment thereof employing oxygen storage components (OSC), cerium and zirconium containing mixed oxides have found use therein, in particular as OSC component in automotive catalysts. As regards the methods for their production, a variety of processes have been employed such as solid state synthesis (e.g. ceramic method and mechanical grinding), liquid to solid synthesis (e.g. precursor method), various precipitation methods, hydrothermal and solvothermal synthesis, sol-gel methods, emulsion and microemulsion methods, impregnation methods, as well as gas to solid synthesis (e.g. chemical vapor deposition). In practice, co-precipitation methods have found wide use. In these cases, from a solution of salts of the desired products the oxides are precipitated with the aid of precipitation or flocculating agents. In these methods, the solubility of the individual compounds plays an important role. In particular, the solubility of the individual compounds must be very similar for avoiding a separation of phases. As a result of this, the use of said method with mixtures consisting of more than two cations becomes difficult. A further disadvantage in these methods is the formation of large amounts of salt containing waste materials during the production of such mixed oxide particles. In addition to this, co-precipitation methods necessitate a considerable number of workup steps including washing, filtration, drying, and calcination. Various studies have shown that flame spray synthesis (FSS) and in particular flame spray pyrolysis (FRP) are suitable for producing oxygen storage materials displaying an improved thermal stability. Thus, Stark et al. in Chem. Comm. 2003, pp. 588-589, were able to produce ceria- zirconia mixed oxides with high surface areas having satisfactory oxygen storage characteristics using such spray flame synthetic methods. Schimmoeller et al. in ChemCatChem. 2011 , 3, 1234-1256, on the other hand, describes the synthesis of ceria-based catalysts made by liquid- fed aerosol flame synthesis (LAFS) including doping of the ceria by zirconium, and wherein it is stated that small amounts of Si added to Ceo.5Zro.5O2 would increase the oxygen exchange capacity of the materials. Jossen et al. J. Am. Ceram. Soc. 2005, 6, 1388-1393 relates to the crite- ria for flame spray synthesis of hollow, shell-like, or inhomogenous oxides including those of ceria, wherein it is explained that the formation of hollow particles often coincides with a fine powder leading to inhomogenous mixtures. In analogy to the co-precipitation methods, flame spray synthesis has also been used for producing ceria-zirconia mixed oxides containing further additives such as e.g. silica and alumina. Thus, in Schuiz et al. in J. Mater. Chem. 2003, vol. 13, pp. 2979-2984 it was found that smaller amounts of silica were able to improve the oxygen storage capacity whereas alumina apparently had no effect thereon. Larger amounts of additives were found to be disadvantageous since these led to the formation of layers which would inhibit the oxygen exchange in the particles.

Jossen et al. Chem. Vap. Deposition 2006, vol. 12, pp. 614-619 investigated the thermal stability of ceria-zirconia mixed oxides using flame spray synthesis. In particular, it was found that ceria-zirconia mixed oxides having a cerium content of 35 wt.-% allowed for a production of par- tides with a high surface area which show an increased resistance to thermal aging. Furthermore, it was found that the addition of aluminum oxide and lanthanum oxide was able to improve the thermal stability. In this respect, the optimum as regards the stabilization effect was found for a mixed oxide consisting of 10 wt.-% lanthanum, 25 wt.-% cerium, and 65 wt.-% zirconium based on the total weight of the rare earth oxides and zirconium oxides.

Wang et al. in Journal of Molecular Catalysis A: Chemical '2011 , vol. 339, pp. 52-60 relates to co-precipitated ceria-zirconia mixed oxides of the formula Ceo.2Zro.8O2 containing 5 wt.-% of rare earth elements such as lanthanum, neodymium, praseodymium, samarium, and yttrium. Wang et al. in Environmental Science and Technology 2010, vol. 44, pp. 3870-3875 concerns ceria- zirconia mixed oxides of the formula Ceo.2Zro.8O2 modified with rare earth elements and in particular with lanthanum, neodymium, praseodymium, samarium, and yttrium as well as their use in a three way catalyst for the treatment of automotive exhaust gases, wherein the rare earth containing ceria-zirconia mixed oxide is obtained by a co-precipitation method. In particular, it was respectively found in Wang et al. that the addition of 5 wt.-% of rare earth oxides to Ceo.2Zro.8O2 had the effect of improving the thermostability as well as the oxygen storage capacity of the resulting material. In particular, the addition of lanthanum, neodymium, and praseodymium showed a clear improvement in comparison with the pure ceria-zirconia mixed oxides. These materials, however, were not produced using flame spray synthesis but rather using a co-precipitation method. Li et al. in Journal of Rare Earths 2011 , vol. 29, no. 6, pp. 544-549, relate to a ceria-zirconia mixed oxide Ceo.8Zro.2O2 containing 5 wt.-% lanthana and which has been produced by a co-precipitation method. Cao et al. in Materials Letters 2008, vol. 62, pp. 2667-2669 on the other hand concerns an oxide ceramic material of the formula La2(CeojZro.3)207 which is obtained from solid state synthesis. On the other hand, in further analogy to the co-precipitation methods, emulsions have also been used for the production of metal oxide particles. Thus, US 2005/0152832 describes a method for the production of nanometer-sized particles by reverse micelle-mediated techniques and their use for the catalytic combustion of methane. CN 102580718 A specifically relates to the production of cerium-zirconium composite materials with the aid of a surface active agent wherein the precursor solution is subject to a homogenizing treatment. In addition to the aforementioned, the use of emulsions in flame spray pyrolysis is for example known from Tani et al. in J. Am. Ceram. Soc. 2003, 6, 898-904 wherein oxide powders including ceria are described which have been prepared by an emulsion combustion method (ECM). Song et al. in Langmuir 2009, 25, 3402-3406, describes the preparation of yttria particles by flame spray pyrolysis from emulsions. Takatori et al. in J. of Nanoparticle Res. 1999, 1 , 197-204 also describes the preparation of ceramic powders by emulsion combustion wherein examples of zirconia-ceria solid solutions are also described. JP 1 1049502 relates to the production of oxide powders by flame spray pyrolysis such as e.g. of lithium manganate and -cobaltate. JP 2001 -072403 concerns the production of a metal oxide from emulsion combustion and specifically describes e.g. the production of aluminosilicates by said method.

Although improvements have been made relative to the methods of obtaining mixed oxide materials containing various additives in addition to the main components and in particular ceria and zirconia, there remains an ongoing need for high performance oxygen storage components which may be produced in a highly efficient and thus cost effective manner for providing cost effective materials. This applies in particular with respect to oxygen storage component materials employed in automotive catalysts which to a large extent is motivated by the costs of the precursor materials and in particular of additives employed in ceria-zirconia mixed oxides for improving their properties. Thus, although improvements have been achieved in view of the flame spray pyrolysis methods which may be performed in a single step, there remains the problem that such methods nevertheless involve the use of larger amounts of precursor materials and in particular of ceria and other rare earth compounds as additive materials for providing the desired performance in oxygen storage capacity in the resulting materials.

DETAILED DESCRIPTION

It is therefore the object of the present invention to provide an improved process for the production of ceria-zirconia mixed oxides. In particular, it is the aim of the present invention to provide a ceria-zirconia mixed oxide material having an excellent oxygen storage capacity and aging resistance in particular relative to the amount of the costly precursor compounds ceria and further additives including rare earth oxides other than ceria for providing the desired features and performance of the oxygen storage materials.

Thus, it has quite surprisingly been found that ceria-zirconia mixed oxide particles obtained from flame spray pyrolysis of dispersions and more generally mixed oxide particles obtainable from flame spray pyrolysis and displaying a narrow particle size distribution in specific ranges display an unexpectedly high performance relative to their oxygen storage capacity when containing one or more further rare earth metals other than ceria and/or yttria, and in particular relative to the amount in which said one or more additives are employed in the ceria-zirconia mixed oxide particles of the present invention. Thus, it has quite unexpectedly been found that not only may a relatively high oxygen storage capacity be obtained in such materials based on the amounts of rare earth metal oxides other than ceria and/or of yttria contained therein, but furthermore these surprisingly show a particularly high stability of the particles upon ageing such that their oxygen storage capacity remains unexpectedly stable under such ageing conditions.

Therefore, the present invention relates to a process for the production of mixed oxide particles comprising:

(1 ) providing a dispersion comprising a disperse phase and a continuous phase, wherein the disperse phase comprises one or more precursor compounds of ceria, one or more precursor compounds of zirconia, and one or more precursor compounds of one or more rare earth oxides other than ceria and/or one or more precursor compounds of yttria;

(2) forming an aerosol of the dispersion provided in step (1 ); and

(3) pyrolyzing the aerosol of step (2) to obtain mixed oxide particles.

Within the meaning of the present invention, the term "zirconia" defines the compound ZrC>2 and in particular defines the compound ZrC>2 in its stoichiometric as well as in any of its non- stoichiometric forms, wherein according the present invention the term "zirconia" further defines ZrC>2 containing variable amounts of HfC>2, wherein again HfC>2 in its stoichiometric as well as in any of its non-stoichiometric forms are designated, respectively. Same applies accordingly with respect to the term "precursor compound of zirconia" which defines a precursor compound of ZrC>2 as well as and in particular also defines a precursor compound of ZrC>2 containing variable amounts of one or more precursor compounds of HfC>2. As regards the amounts of HfC>2 which may be contained in zirconia or in any of the precursor compounds of zirconia calculated as ZrC>2 and HfC>2, respectively, no particular restrictions apply such that any conceivable amounts of HfC>2 and precursor compounds thereof calculated as HfC>2 may be contained therein. According to the present invention it is preferred that the term "zirconia" and "precursor compound of zirconia" designates ZrC>2 and precursor compounds thereof containing from 0 to 3 wt.-% of HfC>2 or one or more precursor compounds thereof calculated as HfC>2, respectively, and preferably containing 0 to 2 wt.-% thereof, wherein more preferably 0 to 1 wt.-% of HfC>2 or one or more precursor compounds thereof calculated as HfC>2, may be contained in ZrC>2 and precursor compounds thereof, respectively.

Furthermore, it is herewith noted that within the meaning of the present invention, and in particular with respect to the particular and preferred embodiments defined in the present application, the term "comprising" is alternatively used as meaning "consisting of, i.e. as specifically and explicitly disclosing corresponding embodiments wherein the subject-matter defined as comprising specific features actually consists of said specific features. According to the present invention, however, the term "comprising" is preferably employed according to its common defi- nition as not limiting the subject-matter to the sole feature or features which it is explicitly stated as comprising.

As regards the dispersion provided in step (1 ) of the inventive process, there is no particular restriction with respect to the type of dispersion which may be provided, nor regarding the method by which said dispersion has been made. Thus, in principle, any suitable dispersion comprising a dispersed phase and a continuous phase may be provided in step (1 ), provided that the dispersed phase comprises the one or more precursor compounds ceria and zirconia in addition to the one or more precursor compounds of one or more rare earth oxides other than ceria and/or one or more precursor compounds of yttria. According to the present invention, it is however preferred that the continuous phase is in the form of a liquid. Furthermore, it is also preferred that the disperse phase is at least partly in the form of a liquid, wherein it is further preferred that the disperse phase according to the inventive process is provided in the form of a liquid in the continuous phase which, preferably, is equally liquid. Accordingly, it is particularly preferred according to the inventive process that both the disperse and the continuous phases provided in step (1 ) are liquid.

With respect to the preferred embodiments of the inventive process wherein the dispersion provided in step (1 ) comprises a liquid as the disperse and continuous phases, there is in principle no restriction relative to the types of liquid components which may be employed for providing the dispersion provided that said liquid components constitute distinct continuous and disperse phases in the dispersion, either in view of the fact that the liquids perse are not miscible and/or by the aid of specific agents which have been added to the disperse and/or continuous phase for avoiding the admixture thereof to a single phase.

According to the present invention it is however preferred that the disperse phase and the continuous phase are respectively made of liquids which are immiscible or wherein the miscibility of the respective liquids is such that 10 vol.-% or less of either liquid phase may dissolve into the other liquid phase, and preferably 5 vol.-% or less, more preferably 3 vol.-% or less, more pref- erably 1 vol.-% or less, more preferably 0.5 vol.-% or less, more preferably 0.1 vol.-% or less, more preferably 0.05 vol.-% or less, more preferably 0.01 vol.-% or less, more preferably 0.005 vol.-% or less, and even more preferably 0.001 vol.-% or less of either of the liquid phases may dissolved in the other liquid phase. According to particularly preferred embodiments of the invention, the dispersion provided in step (1 ) is a water in oil dispersion or an oil in water dispersion, wherein preferably the dispersion is a water in oil dispersion wherein the disperse phase is accordingly of aqueous nature. According to said particularly preferred embodiments, there is no particular restriction neither with respect to the constituents of the "oil" phase nor with regard to the constituents of the "wa- ter" phase such that in principle any conceivable liquids and in particular any conceivable solvent or solvent system may be comprised in the disperse and continuous phases provided that the hydrophobic nature of the "oil" phase is greater than the hydrophobic nature of the "water" phase, and accordingly the hydrophilic nature of the "oil" phase is lower than the hydrophilic nature of the "water" phase. In particular, it is noted that according to the present invention, the words "water" and "oil" as respectively employed in the terms "oil in water" and "water in oil" relative to specific types of preferred dispersion employed in the inventive process only speci- fies the hydrophilic character of the disperse phase being greater than the hydrophilic character of the continuous phases in the case of "water in oil" dispersions and vice versa a hydrophobic character of the disperse phase being greater than the hydrophobic character of the continuous phase in the case of "oil in water" dispersions". Thus the "water" and "oil" as employed in these terms do not by any means further limit the disperse and continuous phases to a greater extent, in particular with respect to the components which may be contained in the respective phases.

Thus, as regards the disperse phase of the dispersion provided in step (1 ) of the inventive process, there is in principle no particular restriction as to the solvent or solvent system which may be contained therein provided that said phase does not admix with the continuous phase of the dispersion. According to particularly preferred embodiments of the inventive process and in particular to embodiments employing a water in oil dispersion, the disperse phase comprised in the dispersion provided in step (1 ) comprises a hydrophilic solvent system, wherein said solvent system may accordingly contain one or more hydrophilic solvents. In this respect, it is noted that the term "hydrophilic" as employed in the present application denotes a hydrophilic character of any one of the solvent systems which may be comprised in the disperse phase as being greater than the hydrophilicity of any of the continuous phases employed in the dispersion provided in step (1 ) according to any of the particular or preferred embodiments of the present invention.

Therefore, according to preferred embodiments of the inventive process, the disperse phase comprises a hydrophilic solvent system, wherein it is preferred that the hydrophilic solvent system comprises one or more hydrophilic solvents. In principle, any one or more hydrophilic solvents may be used in the hydrophilic solvent system of the disperse phase, and in particular any one or more hydrophilic solvents selected from the group of polar solvents. More preferably, the one or more hydrophilic solvents are selected from the group of polar protic and polar aprotic solvents, including mixtures of two or more thereof. As regards the preferred polar solvents and in particular the preferred polar protic and polar aprotic solvents, any conceivable solvents or solvent mixtures may be employed for the hydrophilic solvent system of the disperse phase provided that these display respective polar protic and polar aprotic features wherein, preferably, the polar solvents and in particular the polar protic and polar aprotic solvents are selected from the group consisting of alcohols, diols, polyols, ethers, carboxylic acids, formamides, ni- triles, sulfoxides, esters of carboxylic acids, ketones, lactones, lactames, sulfones, nitrocompounds, alkyl derivates of urea-compounds, water, and mixtures of two or more thereof, more preferably from the group consisting of (Ci-Cs)alcohols, (C2-C6)diols, (Ci-C3)dialkylethers, (Ci-C5)carboxylic acids, alkyl amides, acetonitrile, dimethylsulfoxide, propylene carbonate, (C2- C6)ketones, (C4-C7)lactones, (C4-C7)lactames, nitromethane, sulfolane, 1 ,3 dimethyl-3, 4,5,6- tetrahydro2(1 H)pyrimidinon (tetra methyl urea), dimethylcarbonate, ethylene carbonate, propylene carbonate, water, and combinations of two or more thereof, more preferably from the group consisting of (C2-C4)alcohols, (C2-C4)diols, (C2-C4)ketones, (Ci-C2)dialkylethers, (C2- C4)carboxylic acids, dimethylformamide, acetonitrile, dimethylsulfoxide, water, and combinations of two or more thereof, more preferably from the group consisting of ethanol, methanol, propa- nol, ethylene glycol, 1 ,3-propanediol, 1 ,2-propanediol, dimethylether, diethylether, ethyl- methylehter, acetic acid, propionic acid, acetonitrile, water, and combinations of two or more thereof, more preferably from the group consisting of ethanol, methanol, ethylene glycol, dimethylether, ethylmethylether, acetic acid, acetonitrile, water, and combinations of two or more thereof, more preferably from the group consisting of ethanol, methanol, ethylene glycol, dimethylether, acetonitrile, water, and combinations of two or more thereof, and more preferably from the group consisting of methanol, acetonitrile, water, and combinations of two or more thereof. According to particularly preferred embodiments of the inventive process, the hydrophilic solvent system comprises methanol and/or water, preferably water as the one or more hydrophilic solvents. As noted above, according to particular embodiments of the inventive process, the disperse and continuous phases of the dispersion provided in step (1 ) may contain one or more agents for stabilizing the respective phases and in particular for stabilizing the disperse phase either from admixture with the continuous phase and/or from coalescence of the disperse phase wherein in particular a coalescence of the disperse phase is prevented by the use of one or more of such agents. According to said preferred embodiments, it is particularly preferred that the disperse phase is comprised in droplets, wherein according to particularly preferred embodiments according to which the disperse phase comprises a hydrophilic solvent system, said hydrophilic solvent system is preferably comprised in the droplets. According to said particularly preferred embodiments wherein the disperse phase is contained in droplets, there is no particular re- sthction as to the agent or agents which may be employed for stabilizing said droplets such that in principle any suitable surfactant may be employed to this effect provided that a dispersion containing such droplets may be provided in step (1 ) depending on the liquids and/or solvent systems employed for the disperse and continuous phases of the dispersion. According to preferred embodiments thereof, the droplets are stabilized by one or more emulsifying agents and in particular one or more emulsifying agents as defined in any one of the particular and preferred embodiments of the dispersion as defined in the present application.

Therefore, embodiments of the inventive process are preferred wherein the hydrophilic solvent system is comprised in droplets, wherein the droplets are preferably stabilized by one or more emulsifying agents.

As regards the continuous phase, on the other hand, there is again no particular restriction as to the components which may be contained therein, provided that they may form a separate phase to the disperse phase and accordingly do not admix with the disperse phase provided in the dispersion. According to preferred embodiments of the inventive process and in particular according to embodiments wherein the disperse phase comprises a hydrophilic solvent system, the continuous phase preferably comprises a hydrophobic solvent system. Within the meaning of the present invention, the term "hydrophobic" relative to the solvent system of the continuous phase indicates that the hydrophobicity of said solvent system is greater than the hydrophobicity of the disperse phase depending on the liquid components and in particular depending on the solvent system which is employed for the disperse phase in accordance with any of the particu- lar and preferred embodiments of the inventive process. Thus, according to the present invention, it is preferred that the continuous phase comprises one or more hydrophobic solvents thus forming a hydrophobic solvent system. As regards the one or more hydrophobic solvents which may be employed according to said preferred embodiments, no particular restriction applies, provided that a separate continuous phase may be formed in addition to the disperse phase contained in the dispersion. Thus, by way of example, the one or more hydrophobic solvents may be selected from the group of hydrocarbons, wherein it is preferred that the one or more hydrophobic solvents are selected from the group consisting of aliphatic and aromatic hydrocarbons, heterocyclic compounds, and mixtures of two or more thereof, wherein the aliphatic and aromatic hydrocarbons include hydrophobic derivatives of aliphatic and aromatic hydrocarbons such as alcohols or carboxylic acids, and preferably Ce-alcohols, Ce-carboxylic acids, and/or oils. According to further preferred embodiments, the one or more hydrophobic solvents are selected from the group consisting of aliphatic and aromatic hydrocarbons, wherein even more preferably the one or more hydrophobic solvents comprise one or more aliphatic hydrocarbons. Therefore, embodiments of the inventive process are preferred wherein the continuous phase comprises a hydrophobic solvent system, the hydrophobic solvent system preferably comprising one or more hydrophobic solvents, wherein the one or more hydrophobic solvents are preferably selected from the group consisting of aliphatic and aromatic hydrocarbons, heterocyclic compounds, and mixtures of two or more thereof.

As regards the aliphatic hydrocarbons preferably comprised as one or more of the hydrophobic solvents in the hydrophobic solvent system of the continuous phase according to preferred embodiments of the inventive process, any conceivable aliphatic hydrocarbons may be employed wherein the aliphatic hydrocarbons may principally be branched or unbranched. According to particularly preferred embodiments, the group of aliphatic hydrocarbons from which the one or more hydrophobic solvents may be selected preferably comprises one or more selected from branched and/or unbranched, preferably unbranched aliphatic (C4-Ci2)hydrocarbons, including mixtures of two or more thereof, preferably aliphatic (Cs-Cio)hydrocarbons, more preferably aliphatic (C6-C8)hydrocarbons, more preferably aliphatic (C6-C7)hydrocarbons, and even more preferably one or more selected from branched and/or unbranched, preferably unbranched aliphatic C6-hydrocarbons, wherein even more preferably the group of aliphatic hydrocarbons comprises one or more selected from pentane, hexane, heptane, octane, and mixtures of two or more thereof. According to particularly preferred embodiments of the inventive process, the hydrophobic solvent system comprises pentane and/or hexane as the one or more hydrophobic solvents, and preferably comprises hexane. Concerning the group of aromatic hydrocarbons from which the one or more hydrophobic solvents contained in the hydrophobic solvent system are preferably selected according to preferred embodiments of the inventive process, there is again no particular restriction as to the aromatic hydrocarbons which may be contained therein, wherein preferably the group of aro- matic hydrocarbons comprises one or more selected from aromatic (C6-Ci2)hydrocarbons, including mixtures of two or more thereof, preferably aromatic (C7-Cn)hydrocarbons, more preferably aromatic (C8-Cio)hydrocarbons, more preferably aromatic (Cs-C^hydrocarbons, and even more preferably aromatic Cs-hydrocarbons, wherein even more preferably the group of aromatic hydrocarbons comprises one or more selected from toluene, ethylbenzene, xylene, mesitylene, durene, and mixtures of two or more thereof, and more preferably from toluene, ethylbenzene, xylene, and mixtures of two or more thereof. According to particularly preferred embodiments of the inventive process, the hydrophobic solvent system comprises toluene and/or xylene as the one or more hydrophobic solvents, and preferably comprises xylene. Finally, regarding the heterocyclic compounds from which the one or more hydrophobic solvents comprised in the hydrophobic solvent system may preferably be selected according to preferred embodiments of the inventive process, again no particular restriction applies in their respect such that any suitable heterocyclic compounds may be employed. According to the inventive process it is however particularly preferred that the one or more heterocyclic compounds com- prise one or more selected from N- and O-containing heterocycles, including mixtures of two or more thereof, and more preferably one or more selected from pyrrolidine, pyrrole, piperidine, pyridine, azepane, azepine, tetrahydrofurane, and mixtures of two or more thereof.

As noted above, there is no particular restriction according to the inventive process as to the method by which the dispersion provided in step (1 ) may be produced. Thus, the dispersion may principally be provided as such, or may be produced directly prior to step (2) of forming an aerosol with said dispersion. In particular, it may be advantageous according to the present invention to produce the dispersion directly before the forming of an aerosol depending on the stability of the dispersion provided in step (1 ) which may necessitate its rapid conversion to an aerosol in step (2) for preventing an undesirable coalescence of the disperse phase and/or an equally undesirable admixing of the continuous and disperse phases prior to the formation of an aerosol in step (2) and its subsequent pyrolyzing in step (3).

Therefore, according to preferred embodiments of the inventive process wherein the provision of a dispersion in step (1 ) includes the production of said dispersion, it is particularly preferred that the dispersion provided in step (1 ) is formed by a process comprising:

(1.a) providing a solution comprising one or more precursor compounds of ceria, one or more precursor compounds of zirconia, and one or more precursor compounds of one or more rare earth oxides other than ceria and/or one or more precursor compounds of yttria dissolved in a hydrophilic solvent system;

(1.b) providing a hydrophobic solvent system optionally comprising one or more emulsifying agents; (1.c) dispersing the solution in the hydrophobic solvent system by mixing, preferably by emulsi- fication, for forming a dispersion.

As regards the provision of the mixture in step (1.a) according to preferred embodiments of the inventive process, there is no particular restriction as to the means which are employed for forming a solution comprising the one or more precursor compounds of ceria, zirconia, and of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria provided that a mixture of the former and a hydrophilic solvent system are provided wherein at least a portion of said one or more precursor compounds may be dissolved in the hydrophilic solvent system, respectively. In instances wherein one or more of the precursor compounds is partly insoluble in the hydrophilic solvent system, it is preferred that means of homogenizing the mixture are employed for achieving the dispersion of said insoluble portion of one or more of the precursor compounds which may not be completely dissolved in the hydrophilic solvent system. Thus, according to said particular embodiments of the inventive process, the homogenous mixture may be provided by appropriate means of agitation such as by stirring, shaking, rotating, and sonication, wherein preferably a homogenization of the mixture is achieved by appropriate stirring of the insoluble portions of the one or more precursors in the solution for providing a high dispersion thereof. According to the present invention, however, it is preferred that the one or more precursor compounds of ceria, zirconia, and of the one or more rare earth oxides other than ceria and/or one or more precursor compounds of yttria provided in step (1.a) are respectively soluble in the hydrophilic solvent system which is provided such that a homogenous mixture is provided by the solution of all components in said solvent system. As regards the provision of a hydrophobic solvent system in step (1.b) according to preferred embodiments of the inventive process, there is again no particular restriction in this respect wherein it is however preferred that one or more emulsifying agents are provided together with the hydrophobic solvent system in instances wherein the choice of the hydrophilic and hydrophobic solvent systems does not allow for the formation of a dispersion in the absence of one or more emulsifying agents or in instances wherein a stabilization of the dispersion is desired prior to the formation of an aerosol in step (2), and in particular in instances wherein the delay between the provision of a dispersion in step (1 ) and the formation of an aerosol in step (2) is such that a stabilization by one or more emulsifying agents becomes desirable or necessary. As regards the hydrophilic solvent system which may be provided in step (1.a), the hydrophobic solvent system which may be provided in step (1 .b) as well as the one or more emulsifying agents which may be provided in step (1.b), it is preferred that the aforementioned are chosen among any of the particular and preferred embodiments of the present invention as set out in the present description.

Concerning the dispersing of the solution provided in step (1.a) in the hydrophobic solvent system provided in step (1.b) in step (1.c) according to preferred embodiments of the present in- vention, in principle any suitable procedure may be employed for performing said dispersing provided that a dispersion is formed comprising the solution dispersed in the hydrophobic solvent system. Thus, by way of example, the dispersing of the solution in the hydrophobic solvent system may be achieved by use of a homogenizer. According to preferred embodiments of the inventive process, however, the dispersing of the solution in step (1.c) by mixing is achieved with a rotor-stator homogenizer, with an ultrasonic homogenizer, with a high pressure homogenizer, by microfluidic systems, or by membrane emulsification, wherein even more preferably the dispersing of the solution is achieved by employing a high pressure homogenizer or a rotor- stator homogenizer. According to preferred embodiments thereof, the mixing in step (1 .c) is achieved by use of a rotor-stator homogenizer. According to embodiments of the inventive process which are particularly preferred, the dispersing of the solution in the hydrophobic solvent system in step (1 c) is achieved by emulsification wherein in particular a method of emulsification is employed in step (1.c) wherein one or more emulsifying agents have been provided in step (1 .b) in addition to the hydrophobic solvent system.

According to preferred embodiments of the inventive process wherein one or more emulsifying agents stabilize the droplets of the hydrophilic solvent system according to preferred embodiments of the inventive process and in particular in embodiments of the inventive process involving the provision of a solution according to step (1 .a) followed by the provision of a hydrophobic solvent system in step (1.b) and the dispersing of said solution in said hydrophobic solvent system by mixing in step (1.c), there is in principle no particular restriction as to the one or more emulsifying agents which may be employed in said embodiments provided that a dispersion comprising a disperse phase and a continuous phase according to any of the particular and preferred embodiments as described in the present description may be obtained. Thus, by way of example, the one or more emulsifying agents preferably employed in the inventive process may be selected from the group consisting of ionic and nonionic surfactants, as well as from mixtures of one or more ionic surfactants with one or more nonionic surfactants. According to particularly preferred embodiments of the inventive process, however, the one or more emulsifying agents comprise one or more nonionic surfactants.

Therefore, embodiments of the inventive process are particularly preferred wherein the one or more emulsifying agents are selected from the group consisting of ionic and nonionic surfactants, including mixtures thereof, wherein preferably the one or more emulsifying agents are selected from a group of nonionic surfactants.

As regards the one or more ionic surfactants which are preferably comprised by the one or more emulsifying agents preferably used in the inventive process, there is no particular restriction as to the ionic surfactants which may be employed to this effect, provided that they are suitable for the formation and/or stabilization of the droplets of the hydrophilic solvent system of the disperse phase comprised in the dispersion provided in step (1 ) of the inventive process and are in particular suitable for the dispersion of a solution comprising the one or more precursor compounds of ceria, zirconia, and of the one or more rare earth oxides other than ceria and/or of yttria in a hydrophobic solvent system preferably by emulsification according to step (1 .c) of preferred embodiments of the inventive process. Thus, in principle, the one or more ionic surfactants may comprise any one or more of an anionic surfactant, of a cationic surfactant, and/or of a zwitterionic surfactant. As regards the one or more anionic surfactants which may be com- prised by the one or more ionic surfactants comprised by the one or more emulsifying agents of preferred embodiments of the inventive process, again no particular restrictions apply in their respect provided that a dispersion according to step (1 ) or preferably according to step (1.c) of preferred embodiments of the inventive process may be obtained. Thus, by way of example, the one or more anionic surfactants may be selected from the group consisting of salts of (C6-Ci8)sulfate, (C6-Cis)ethersulfate, (C6-Ci8)sulfonate, (C6-Ci8)sulfosuccinate (C6- Cis)phosphate, (C6-Cis)carboxylate, and mixtures of two or more thereof, more preferably from the group consisting of salts of (C8-Ci6)sulfate, (C8-Ci6)ethersulfate, (C8-Ci6)sulfonate, (Cs- Ci6)sulfosuccinate, (C8-Ci6)phosphate, (C8-Ci6)carboxylate, and mixtures of two or more thereof, more preferably from the group consisting of salts of (Cio-Ci4)sulfate, (Cio-Ci4)ethersulfate, (Cio-Ci4)sulfonate, (Cs-C jsulfosuccinate, (Cio-Ci4)phosphate, (Cio-Ci4)carboxylate, and mixtures of two or more thereof, and more preferably from the group consisting of salts of lau- rylsulfate, laurylsulfonate, dioctyl sulfosuccinate, laurylphosphate, laurate, and mixtures of two or more thereof. As regards the counterions to the anionic surfactants which may employed in the aforementioned preferred embodiments of the inventive process, any suitable counterion or combination of counterions may be employed. According to preferred embodiments, however, the counterion is selected from the group consisting of H⁺, alkali metals, alkaline earth metals, ammonium, and combinations of two or more thereof, more preferably from the group consisting of H⁺, Li⁺, Na⁺, K⁺, ammonium, and combinations of two or more thereof, more preferably from the group consisting of Na⁺, K⁺, ammonium, and combinations of two or more thereof, wherein even more preferably the counterion is Na⁺ and/or ammonium, and preferably Na⁺.

Concerning the one or more cationic surfactants preferably comprised among the ionic surfactants preferably comprised by the one or more emulsifying agents employed in particular and preferred embodiments of the inventive process, again no particular restrictions apply in their respect neither regarding the type of one or more cationic surfactants which may be employed, nor with respect to the number of different cationic surfactants which may be possibly used in combination. Thus, by way of example, the one or more cationic surfactants preferably employed in the inventive process may be selected from the group consisting of primary, secondary, tertiary, and quaternary ammonium compounds, including mixtures of two or more thereof, wherein more preferably the cationic surfactants comprise one or more quaternary ammonium compounds, preferably selected from the group consisting of salts of (Cs- Ci₈)trimethylammonium, (C₈-Ci₈)pyridinium, benzalkonium, benzethonium, dimethyldioctade- cylammonium, cetrimonium, dioctadecyldimethylammonium, and mixtures of two or more thereof, and more preferably from the group consisting of salts of cetyltrimethylammonium, do- decyltrimethylammonium, cetylpyridinium, benzalkonium, benzethonium, dimethyldioctade- cylammonium, cetrimonium, dioctadecyldimethylammonium. As regards the counterions to the cationic surfactants which may employed in the aforementioned preferred embodiments of the inventive process, any suitable counterion or combination of counterions may be employed. According to preferred embodiments, however, the counterion is selected from the group consisting of halides, carbonates, hydroxide, nitrate, phosphate, sulfate, and combinations of two or more thereof, more preferably from the group consisting of chloride, fluoride, bromide, hydrogen carbonate, hydroxide, nitrate, sulfate, and combinations of two or more thereof, wherein more preferably the counterion is chloride and/or nitrate, and preferably chloride.

Finally, among the ionic surfactants preferably comprised by the one or more emulsifying agents preferably used in the inventive process, one or more zwitterionic surfactants may be equally be contained therein, wherein again no particular restrictions apply neither with respect to the type nor with respect to the number of different zwitterionic surfactants which may be employed in combination with one another for obtaining a dispersion according to particular and preferred embodiments of the inventive process as defined in the present application. According to particularly preferred embodiments, however, the one or more zwitterionic surfactants com- prise one or more betaines and more preferably one or more betaines including cocoamidopro- pyl betaine or alkyldimethylamine oxide.

Therefore, according to preferred embodiments of the inventive process employing one or more emulsifying agents being selected from the group consisting of ionic and nonionic surfactants, it is particularly preferred that the ionic surfactants comprise one or more anionic surfactants. I ndependently thereof or in addition thereto, it is further preferred that the ionic surfactants comprise one or more cationic surfactants, wherein independently thereof or in addition thereto it is further preferred that the ionic surfactants comprise one or more zwitterionic surfactants. According to embodiments of the inventive process which are particularly preferred, however, the one or more emulsifying agents are selected from the group consisting of nonionic surfactants. In this respect, as with respect to the ionic surfactants which may be employed in the inventive process, there is again no particular restriction neither with respect to the type nor with respect to the number of nonionic surfactants which may be employed provided that a disper- sion as defined in step (1 ) and in particular in step (1.c) of any of the particular and preferred embodiments of the inventive process may be provided. Thus, by way of example, the nonionic surfactants may be selected from the group consisting of (C8-C22)alcohols, (C6-C2o)alcohol eth- oxylates with 1 to 8 ethylene oxide units, (C6-C2o)alkyl polyglycosides, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, glucoside alkyl ethers, polyoxyethylene glycol alkylphenol ethers, glycerol alkyl esters, sorbitan alkyl esters, polyoxyethylene glycol sorbitan alkyl esters, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof, wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci4-C2o)alcohols, (Cs-Cisjalcohol ethox- ylates with 2 to 6 ethylene oxide units, (Cs-Ci8)alkyl polyglycosides, octaethylene glycol mono- dodecyl ether and/or pentaethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphenol ethers, preferably triton X-100, nonoxynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbi- tan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof, wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci6-Ci8)alcohols, (Ci6-Ci8)alcohol ethoxylates with 2 to 6 ethylene oxide units, (Cs-Ci4)alkyl polyglycosides, preferably cetyl alcohol, stearyl alcohol, oleyl alcohol, and mixtures of two or more thereof, octaethylene glycol monododecyl ether and/or pen- taethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphenol ethers, nonoxynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan oleate, polyoxyethylene (20) sorbitan monolaurate, polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20) sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, Stearyl-EC>2, polyglyceryl-2- dipolyhydroxystearate, polyglyceryl-distearate, C13/15 - PEG3, C13 - PEG2, glyceryl monooleate, C16/18 - PEG2, oleyl - PEG2, PEG20 - sorbitan monooleate, functionalized poly- isobutene, C16/18 - PEGg, and mixtures of two or more thereof, and more preferably from the group consisting of polyglyceryl-2-dipolyhydroxystearate, diglyceryl-distearate, triglyceryl- distearate, C13/15 - PEG3, C13 - PEG2, glyceryl monooleate, sorbitan monooleate, polyglycer- ol-3-polyricinoleate, C16/18 - PEG2, oleyl - PEG2, PEG20 - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEGg, and mixtures of two or more thereof. According to particularly preferred embodiments of the present invention, the one or more preferred nonionic surfactants employed as the emulsifying agent is selected from the group consisting of polyglyceryl-2- dipolyhydroxystearate, diglyceryl-distearate, triglyceryl-distearate, and mixtures of two or more thereof, wherein it is even more preferred that the nonionic surfactant comprises polyglycerol-3- polyricinoleate.

As noted in the foregoing relative to the particular and preferred embodiments of the inventive process involving the use of one or more emulsifying agents, no particular restriction applies neither with respect to the type nor regarding the number of different emulsifying agents which may be employed to this effect. Besides this, also no particular restrictions apply relative to the amount of the one or more emulsifying agents which may be used in particular and preferred embodiments of the inventive process provided that a dispersion according to step (1 ) and in particular according to step (1.c) may be achieved. Thus, by way of example, the amount of the emulsifying agent contained in the dispersion provided according to particular and preferred embodiments of the inventive process may range anywhere from 0.01 to 20 wt.-% based on the total weight of the dispersion provided in step (1 ). According to preferred embodiments of the inventive process, the emulsifying agent is contained in the dispersion in an amount of from 0.05 to 10 wt.-%, and more preferably of from 0.1 to 7.0 wt.-%, more preferably from 0.5 to 5.0 wt.-%, more preferably from 0.8 to 4.0 wt.-%, more preferably from 1 to 3.0 wt.-%, more preferably from 1 .3 to 2.5 wt.-%, more preferably from 1.5 to 2.0 wt.-%, and even more preferably from 1 .7 to 1 .9 wt.-%.

Besides the aforementioned characteristics of the dispersion provided in step (1 ) of the inventive process in particular relative to the type and amount of its constituents according to particular and preferred embodiments of the present invention, there is in principle no particular restriction relative to the further characteristics of the dispersion provided that it may be suitably employed for the formation of an aerosol in step (2) of the inventive process. This applies in particular relative to the grade of dispersion achieved by the disperse phase contained in the dispersion which is primarily related by the particle size and particle size distribution of a given dispersion. Thus, as regards the average particle size of the dispersion and in particular of the droplets of the disperse phase contained in the continuous phase of the dispersion, no particu- lar restriction applies in this respect such that, by way of example, the average particle size D50 of the disperse phase may be comprised in the range of anywhere from 0.05 to 20 μιτι. According to preferred embodiments of the inventive process, however, the dispersion provided in step (1 ) displays an average particle size D50 comprised in the range of from 0.1 to 15 μιτι, and more preferably of from 0.2 to 10 μιτι, more preferably of from 0.5 to 9 μιτι and more preferably of from 1 to 5 μιτι. According to particularly preferred embodiments of the inventive process, the average particle size of D50 of the disperse phase provided in step (1 ) is comprised in the range of from 2 to 4 μιτι.

Same applies accordingly relative to the particle size distribution displayed by the dispersion provided in step (1 ) such that in principle any conceivable particle size distribution may be employed relative to the particles and in particular to the droplets contained in the dispersion. Thus, by way of example, the D90 values which may be displayed by the dispersion provided in step (1 ) may be comprised in the range of anywhere from 0.1 to 50 μιτι. According to the inventive process it is however preferred that the D90 value of the disperse phase provided in step (1 ) is comprised in the range of from 0.5 to 30 μιτι and more preferably of from 1 to 22 μιτι, more preferably of from 2 to 16 μιτι, and more preferably of from 3 to 8 μιτι. According to particularly preferred embodiments of the inventive process, the disperse phase provided in step (1 ) displays a D90 value comprised in the range of from 4 to 6 μιτι. As employed in the present application, the average particle size value D50 indicates that considering the particle sizes of all particles, i.e. the cumulative particle size distribution, 50 wt.-% thereof have particle sizes less than the indicated D50 value. Same applies accordingly relative to the D90 values as employed in the present application indicating that 90 wt.-% of the particles have a smaller particle size than the indicated value for D90, as well as for the D10 values defined in the present application which accordingly indicate that 10 wt.-% of the particles have a smaller particle size than the indicated D10 value. Furthermore, within the meaning of the present invention, the term "particle size" refers to the diameter of a particle and preferably to its average diameter. According to a definition which is alternatively preferred, the term "particle diameter" refers to the largest diameter, i.e. to the largest dimension of the particle.

Concerning the dispersion provided in step (1 ) of the inventive process, there is no particular restriction with respect to the amount of the one or more precursor compounds of ceria, zirco- nia, or of the one or more rare earth oxides other than ceria and/or of yttria, provided that depending on the specific parameters and conditions which are employed in the steps of providing the dispersion in step (1 ), of forming the aerosol from said dispersion in step (2), and of pyrolyz- ing the aerosol in step (3), mixed oxide particles comprising ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce and/or yttria are obtained. Thus, as regards the one or more rare earth oxides other than ceria provided in step (1 ) of the inventive process, there is no particular restriction according to the present invention neither with respect to the type nor with respect to the number of the one or more precursor compounds of one or more rare earth oxides other than ceria which may be provided. According to the present inven- tion it is however preferred that said one or more rare earth oxides other than ceria comprise one or more of lanthana, praseodymia, and neodymia, including mixtures of two or three thereof, wherein it is further preferred that the one or more rare earth oxides other than ceria comprise lanthana and/or neodymia. According to particularly preferred embodiments of the present invention, the one or more rare earth oxides other than ceria provided in step (1 ) of the inventive process include lanthana, wherein even more preferably the rare earth oxide other than ceria is lanthana.

According to the present invention, unless otherwise specified, the designation of the rare earth oxides does not refer to a particular type thereof, in particular relative to the oxidation state of the rare earth metal, such that in principle any one or more rare earth oxides may be designated. Thus, by way of example, unless otherwise specified, the term "ceria" principally refers to the compounds CeC>2, Ce2C>3, and any mixtures of the aforementioned compounds. According to a preferred meaning of the present invention, however, the term "ceria" designates the compound CeC>2. Same applies accordingly relative to the term "praseodymia" such that in general said term designates any one of the compounds Pr2C>3, PreOn, PrC>2, and any mixtures of two or more thereof. According to a preferred meaning of the present invention, the term "praseodymia" designates the compound Pr2C>3.

Therefore, according to preferred embodiments of the inventive process, the one or more rare earth oxides other than ceria is selected from the group consisting of lanthana, praseodymia, neodymia, and mixtures of two or three thereof, wherein the one or more rare earth oxides preferably comprises lanthana and/or neodymia, preferably lanthana, wherein even more preferably the rare earth oxide other than ceria is lanthana. Concerning the concentration of the one or more precursor compounds of the one or more rare earth oxides other than ceria, there is again no particular restriction according to the present invention as to the amounts in which said compounds may be provided in step (1 ) of the in- ventive process. Same applies accordingly with respect to the one or more precursor compounds of yttria according to embodiments containing the same. Thus by way of example, the concentration of the one or more precursor compounds of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria calculated as their respective oxides contained in the dispersion provided in step (1 ) may be comprised in the range of anywhere from 0.01 to 5 wt.-% based on the total weight of the dispersion provided in step (1 ), wherein preferably the concentration thereof is comprised in the range of from 0.05 to 2 wt.-%, more preferably from 0.08 to 1 wt.-%, more preferably from 0.1 to 0.5 wt.-%, more preferably from 0.15 to 0.35 wt.-%, and more preferably from 0.18 to 0.3 wt.-%. According to particularly preferred embodiments of the present invention, the concentration of the one or more precursor compounds of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria calculated as their respective oxides is comprised in the range of from 0.21 to 0.27 wt.-% based on the total of the dispersion provided in step (1 ). As regards the concentration of the one or more precursor compounds of ceria which may be contained in the dispersion provided in step (1 ), as for the one or more precursor compounds of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria, there is again no particular restriction in this respect provided that depending on the type and amount of the other components provided in the dispersion of step (1 ) and the specific steps and parameters chosen in steps (2) and (3) of the inventive process allow for the generation of mixed oxide particles. Thus, by way of example, the concentration of the one or more precursor compounds of ceria calculated as CeC>2 contained in the dispersion provided in step (1 ) may be comprised anywhere in the range of from 0.05 to 15 wt.-% based on the total weight of the dispersion provided in step (1 ), wherein preferably the concentration of the one or more precursor compounds of ceria is comprised in the range of from 0.1 to 10 wt.-%, more preferably of from 0.5 to 5 wt.-%, more preferably of from 0.8 to 3 wt.-%, more preferably of from 1 to 2.5 wt.-%, and more preferably of from 1.4 to 2.2 wt.-%. According to particularly preferred embodiments of the present invention, the concentration of the one or more precursor compounds of ceria calculated as CeC>2 contained in the dispersion provided in step (1 ) is com- prised in the range of from 1.7 to 2.0 wt.-%.

Finally, concerning the one or more precursor compounds of zirconia provided in step (1 ) of the inventive process, as for the one or more precursor compounds of ceria or of the other precursor compounds of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria, again no particular restrictions apply in this respect for the same reasons as mentioned in the foregoing relative to the other components of the dispersion provided in step (1 ). Thus, by way of example, the concentration of the one or more precursor compounds of zirconia calculated as ZrC>2 contained in the dispersion provided in step (1 ) may be comprised in the range of from anywhere from 0.05 to 15 wt.-% based on the total weight of the dispersion provided in step (1 ), wherein preferably the concentration of the one or more precursor compounds of zirconia is comprised in the range of from 0.1 to 10 wt.-%, more preferably of from 0.5 to 7 wt.-%, more preferably of from 1 to 5 wt.-%, more preferably of from 1.5 to 4 wt.-%, and more preferably of from 1 .8 to 3 wt.-%. According to particularly, preferred embodiments of the present invention, the concentration of the one or more precursor compounds of zirconia contained in the dispersion provided in step (1 ) is comprised in the range of from 2.1 to 2.3 wt.-%.

As regards the relative amounts of the disperse phase and continuous phase of the dispersion provided in step (1 ) of the inventive process, the weight ratio of the aforementioned is not particularly restricted provided that the specific steps and parameters chosen in steps (2) and (3) of the inventive process allow for the generation of mixed oxide particles. Thus, by way of exam- pie, the concentration of the disperse phase in the dispersion provided in step (1 ) may be comprised in the range of from 1 to 80 wt.-% based on the total weight of the dispersion, wherein preferably the concentration of the disperse phase is comprised in the range of from 5 to 70 wt.-%, more preferably of from 10 to 60 wt.-%, more preferably of from 20 to 55 wt.-%, more preferably of from 30 to 50 wt.-%, and more preferably of from 35 to 45 wt.-%. According to par- ticularly preferred embodiments of the inventive process, the concentration of the disperse phase in the dispersion provided in step (1 ) is comprised in the range of from 40 to 42 wt.-% based on the total weight of the dispersion.

Concerning the one or more precursor compounds of ceria comprised in the dispersion provid- ed in step (1 ) of the inventive process, there is no particular restriction neither with respect to the particular type or number of precursor compounds which may be employed nor with respect to the amount in which they may be provided in the dispersion provided that depending on the further components provided in the dispersion and the specific means of executing steps (1 ), (2) and (3) of the inventive process affords mixed oxide particles in step (3). The same applies ac- cordingly with respect to the one or more precursor compounds of zirconia as well as with respect to the one or more precursor compounds of the one or more rare earth oxides other than ceria and with respect to the one or more precursor compounds of yttria. Thus, as regards the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprised in the dispersion provided in step (1 ), any one or more of said precur- sor compounds may be provided in any suitable form provided that their interaction in the disperse phase and in particular with the hydrophilic solvent system preferably comprised by the disperse phase and/or with the further components of the disperse phase such as one or more emulsifying agents preferably contained therein allows for the formation of mixed oxide particles in step (3) in particular when applying the methods for forming an aerosol employed in step (2) and when pyrolizing said aerosol in step (3) according to any of the particular and preferred embodiments of the inventive process. Thus, by way of example, the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria may be any suitable compound of said rare earth metals or yttrium, wherein it is preferred that one or more salts of said rare earth metals and/or of yttrium be provided in step (1 ) of the inventive process.

As regards the preferred salts of the rare earth metals and/or of yttrium which may be employed in the inventive process, any conceivable salts may be employed, wherein it is preferred that the one or more salts may completely dissolve in the disperse phase provided in step (1 ), wherein the type of salts chosen may accordingly depend on the type and amount of salts chosen for the other precursor compounds provided in step (1 ) and in particular on the further components of the disperse phase and in particular on the hydrophilic solvent system and/or on the one or more emulsifying agents preferably comprised in the disperse phase according to any of the particular and preferred embodiments of the inventive process. Thus, according to the present invention, it is particularly preferred that the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprise one or more salts selected from the group consisting of nitrates, nitrites, halides, sulfates, sulfites, phosphates, carbonates, hydroxides, carboxylates, alcoholates, and mixtures of two or more thereof, more preferably from the group consisting of nitrates, fluorides, chlorides, bromides, hydrogensulfates, hy- drogenphosphates, dihydrogenphosphates, hydrogencarbonates, hydroxides, (C6- Cio)carboxylates, (C2-C5) alcoholates, and mixtures of two or more thereof, more preferably from the group consisting of nitrates, chlorides, bromides, hydrogensulfates, dihydrogenphos- phates, hydroxides, (C7-Cg)carboxylates, (C3-C4)alcoholates, and mixtures of two or more thereof, more preferably from the group consisting of nitrates, chlorides, hydrogensulfates, hydroxides, Cs-carboxylates, C3-alcoholates, and mixtures of two or more thereof. According to particularly preferred embodiments of the present invention, the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprise one or more salts are selected from nitrates and/or chlorides, wherein even more preferably the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprise one or more nitrates.

According to the present invention, it is further preferred that according to the preferred embod- iments, wherein the one or more precursor compounds comprise one or more salts, said salts do not lower the solubility of the one or more further precursor compounds as a result of the specific type of salt which is used. Furthermore, it is preferred that the salts which are preferably used as the one or more precursor compounds do not have a negative impact on the apparatus which is used and in particular does not generate reactive side products which may damage said apparatus, e.g., by corrosion thereof. Accordingly, it is preferred according to the present invention that the dispersion provided in step (1 ) does not contain any halides and in particular does not contain any fluorides, chlorides, and/or bromides and even more preferably does not contain any fluorides and/or chlorides. Within the meaning of the present invention, the dispersion provided in step (1 ) does not contain any halides when no substantial amount of a halide- containing salt is present in the dispersion provided in step (1 ), wherein the term "substantial" as employed for example in the terms "substantially not", or "not any substantial amount of within the meaning of the present invention respectively refer to there practically being not any amount of said component in the dispersion provided in step (1 ) and/or in the aerosol formed in step (2) of the inventive process, wherein preferably 0.1 wt.-% or less of said one or more components is contained therein based on the total weight of the mixture and/or of the liquids and/or solids contained in the aerosol, preferably an amount of 0.05 wt.-% or less, more preferably of 0.001 wt.-% or less, more preferably of 0.0005 wt.-% or less, and even more preferably of 0.0001 wt.- % or less.

Concerning the dispersion provided in step (1 ) of the inventive process, there is also no particu- lar restriction which would apply relative to any further compounds which may be contained therein, provided that mixed oxide particles according to any of the particular or preferred embodiments of the present invention may be formed in step (3). Thus, any suitable auxiliary agent may further be comprised in the dispersion of step (1 ) and/or any further compound or compounds may be provided therein for incorporation into the mixed oxide particles formed in step (3) of the inventive process. In this respect, it is particularly preferred that one or more transition metal-containing compounds be provided in step (1 ) as precursor compounds for the incorporation of said one or more transition metals into the mixed oxide particles generated in step (3) of the inventive process. According to particularly preferred embodiments, one or more platinum group metals are included in the dispersion of step (1 ) for incorporation thereof in the metal ox- ide particles resulting from the inventive process. According to the present invention, it is further preferred that the one or more platinum group metals are preferably selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, and mixtures of two or more thereof, more preferably from the group consisting of Rh, Pd, Pt, and mixtures of two or more thereof, wherein more preferably the platinum group metal is Pd and/or Pt, preferably Pd.

Regarding the preferred embodiments of the inventive process, wherein one or more transition metals and in particular one or more platinum group metals is further added to the dispersion provided in step (1 ) of the inventive process, there is in principle no particular restriction as to the amounts in which said one or more metals may be added thereto, provided that mixed oxide particles according to particular and/or preferred embodiments of the present invention may be formed in step (3) of the inventive process, in particular with respect to the content of the rare earth oxides other than ceria and/or of yttria in the mixed oxide particles formed in step (3). Thus, by way of example, the one or more transition metals and in particular the one or more platinum group metals may be included in the dispersion provided in step (1 ) in an amount rang- ing anywhere from 0.001 to 5 wt.-% calculated as the metal based on the total weight of the dispersion provided in step (1 ), wherein preferably the amount thereof is comprised in the range of from 0.003 to 2 wt.-%, more preferably of from 0.005 to 1 wt.-%, more preferably of from 0.008 to 0.5 wt.-%, more preferably of from 0.01 to 0.3 wt.-%, more preferably of from 0.03 to 0.2 wt.-%, and more preferably of from 0.05 to 0.15 wt.-%.

Concerning the formation of an aerosol in step (2), on the other hand, there is again no particular restriction according to the present invention as to the means which may be employed for forming such an aerosol provided that it may be pyrolyzed in step (3) of the inventive process. Thus, by way of example, the aerosol may be formed by any appropriate means for dispersing the dispersion provided in step (1 ) in a gaseous medium such as by spraying the dispersion provided in step (1 ) into said medium. According to a preferred embodiment of the present invention, the dispersion provided in step (1 ) is sprayed into a gas stream for obtaining a stream of said aerosol which may then be conducted into a pyrolyzing zone for achieving step (3) of the inventive process.

As regards the step of pyrolyzing of the aerosol provided in step (2) of the inventive process, there is again no particular restriction as to the method which is employed for achieving said pyrolysis, provided that at least a portion of the aerosol is converted to mixed oxide particles as a result of said thermal treatment. Thus, by way of example, the pyrolysis in step (3) may be achieved with the aid of any suitable heat source of which the temperature is sufficient for pyrolyzing at least a portion of the aerosol provided in step (2). According to the present invention, the process for the production of mixed oxide particles is conducted in a continuous mode, wherein the aerosol according to particular and preferred embodiments of the present invention is provided as a gas stream which is allowed to pass a pyrolyzing zone for obtaining mixed oxide particles from at least a portion of said aerosol in the gas stream exiting the pyrolyzing zone. According to said preferred embodiments of the present invention wherein the pyrolysis is con- ducted in a continuous mode, there is no particular restriction as to the weight hourly space velocity of the aerosol gas stream which is conducted to the pyroylsing zone, nor is there any restriction as to the extent of the pyrolyzing zone provided that the weight hourly space velocity is chosen such depending on the extent of the pyrolyzing zone at least a portion of the aerosol may be pyrolyzed in step (3) for obtaining mixed oxide particles.

As regards the gas in which the aerosol is formed in step (2) of the inventive process, there is again no particular restriction regarding its composition such that it may contain one type of gas or several different types of gases. Accordingly, the gas employed for providing the aerosol in step (2) may consist of one or more inert gases, wherein according to the present invention said one or more inert gases do not react under the conditions of pyrolysis in step (3) of the inventive process. According to the present invention, it is however preferred that at least a portion of the gas employed for forming an aerosol in step (2) is a gas which reacts with at least a portion of the dispersion provided in step (1 ), wherein it is further preferred that said gas has an oxidizing effect on the dispersion provided in step (1 ), in particular during pyrolysis of the mixture in step (3). According to said embodiments wherein at least a portion of the gas contained in the aerosol formed in step (2) acts as an oxidizing agent towards the mixture in step (1 ), there is no particular restriction as to the type of gas which may be used to this effect provided that it may oxidize at least a portion of the dispersion provided in step (1 ). According to said preferred embodiments of the present invention it is further preferred that the portion of the gas contained in the aerosol provided in step (2) which has an oxidizing effect on the dispersion provided in step (1 ) reacts with at least a portion of the mixture during pyrolysis in step (3), wherein said reaction is exothermic for providing at least a portion of the heat source required in step (3) for the pyrolysis of the dispersion provided in step (1 ). As regards the type of gas which may be used according to said particularly preferred embodiments, there is again no particular re- striction provided that it may react with at least a portion of the dispersion provided in step (1 ) in an exothermic fashion for providing at least part of the heat necessary for the pyrolysis in step (3). According to particularly preferred embodiments of the present invention, the oxidizing gas comprised in the aerosol in step (2) comprises oxygen, wherein more preferably the oxidizing gas contained in the aerosol of step (2) is air, and more preferably air enriched with oxygen. According to said particularly preferred embodiments it is further preferred that the oxidizing gas contained in the aerosol of step (2) is oxygen.

As regards the pyrolysis performed in step (3) of the inventive process, there is no particular restriction as to the temperature at which said step is performed, provided that mixed oxide particles according to the particular and preferred embodiments of the present invention are produced therein, in particular with respect to the content of the rare earth oxides other than ceria and/or of yttria contained therein. Thus, by way of example, the temperature at which the pyrolysis is performed may be comprised in the range of anywhere from 800 to 4,000°C, wherein preferably the temperature in step (3) is comprised in the range of from 900 to 3,500°C, more preferably of from 1 ,000 to 3,000°C, more preferably of from 1 ,100 to 2,500°C, and more preferably of from 1 , 150 to 2,000°C. According to particularly preferred embodiments of the present invention, pyrolysis in step (3) is performed at a temperature comprised in the range of from 1 ,200 to 1 ,500°C.

Further regarding the pyrolysis in step (3), the preferred temperatures at which said step is performed according to any of the particular and preferred embodiments of the inventive process generally refers to the temperature of the reaction zone in which pyrolysis takes place and preferably to the average temperature measured therein. Thus, in view of the temperature gradient often formed in the reaction zone in which pyrolysis takes place, the aforementioned preferred temperatures do not necessarily reflect the temperature which may be measured in the hottest region of the reaction zone in which pyrolysis takes place. Concerning the hottest region of the reaction zone in which pyrolysis in step (3) of the inventive process preferably takes place, there is no general restriction according to the present invention as to which temperatures may be employed provided that mixed oxide particles may be formed in said step, and in particular mixed oxide particles according to any of the particular and preferred embodiments of the present application. Thus, by way of example, the temperature in the hottest region of the reaction zone in which pyrolysis takes place may range anywhere from 400 to 4,000 °C, wherein preferably the temperature in the hottest region is comprised in the range of 1 ,200 to 3,500 °C. According to particularly preferred embodiments of the inventive process, however, the temperature of the hottest region in which pyrolysis in step (3) takes place is comprised in the range of from 1 ,500 to 3,000 °C.

Therefore, embodiments of the inventive process are preferred wherein pyrolysis in step (3) is performed in an atmosphere containing oxygen, preferably in air, more preferably in air enriched with oxygen, and even more preferably in an oxygen atmosphere. According to particularly preferred embodiments of the inventive process, pyrolysis in step (3) is conducted using a burner configuration in which the pyrolysis of the aerosol is assisted and guided by a pilot flame located in proximity such as to achieve a temperature of pyrolysis ac- cording to any of the particular and preferred embodiments of the inventive process. As regards the type of pilot flame which may be employed according to said preferred embodiments, no particular restriction applies provided that the desired temperature in the pyrolysis zone may be achieved. Thus, by way of example, the fuel employed for generating the pilot flame is not par- ticularly restricted such that in principle any suitable combustant may be employed. According to preferred embodiments thereof, however, a combustant is employed which generates little to no carbonaceous residues under the chosen conditions of use. Thus, by way of example, any suitable hydrocarbon may be employed to this effect, wherein preferably short chain saturated and/or unsaturated hydrocarbons with one to three C atoms and preferably with one or two C atoms including mixtures of two or more thereof may be employed as the combustant of the pilot flame. According to particularly preferred embodiments thereof, methane and/or ethylene is employed as the combustant in the pilot flame. Regarding the oxidant used for the combustion of the fuel employed in the pilot flame, again no particular restriction applies provided that a temperature comprised in the particular and preferred ranges of the inventive process may be achieved and that furthermore little to no carbonaceous residues are generated. Thus, by way of example, any gas containing an appropriate oxidizing agent and preferably an oxidizing agent in the form of a gas may be employed, wherein preferably a gas containing oxygen is employed, and more preferably a gas containing one or more inert gases such as nitrogen may be employed for generating the pilot flame. According to particularly preferred embodiments thereof, a mixture of air and oxygen is employed as the oxidizing agent for the combustion of the fuel in the pilot flame, wherein more preferably oxygen gas is used as the oxidizing agent.

With respect to the composition of the aerosol formed in step (2), no particular restriction applies relative to the weight ratio of the dispersion to the dispersing gas in which the aerosol is formed. Thus, by way of example, the weight ratio of the dispersion to the gas phase of the aerosol may range anywhere from 1 to 20, wherein preferably the weight percent ratio of dispersion to gas in the aerosol formed in step (2) is comprised in the range of from 3 to 15, and even more preferably a weight ratio comprised in the range of 8 to 12 is employed in particularly preferred embodiments of the inventive process.

In addition to providing a process for the production of mixed oxide particles, the present invention relates to the mixed oxide particles per se which are obtained according to the inventive process, as well as to mixed oxide particles which are obtainable according to any of the particular and preferred embodiments of the inventive process irrespective of the actual method ac- cording to which the mixed oxide particles are actually produced.

Therefore, the present invention also relates to mixed oxide particles obtainable and/or obtained, preferably obtained according to any of the particular and preferred embodiments of the inventive process.

Furthermore, the present invention also relates to mixed oxide particles obtainable from flame spray pyrolysis, wherein the particles comprise ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce, and/or yttria, and wherein the particle size distribution is such that the average diameter D50 is comprised in the range of from 0.3 to 1.4 μιη, preferably from 0.35 to 1 .35 μιτι, more preferably from 0.4 to 1.3 μιτι, more preferably from 0.45 to 1.25 μιτι, more preferably from 0.5 to 1.2 μιτι, and more preferably from 0.55 to 0.9 μιτι, and the di- ameter D10 is comprised in the range of from 0.01 to 0.28 μιτι, preferably from 0.04 to 0.26 μιτι, more preferably from 0.06 to 0.24 μιτι, more preferably from 0.08 to 0.22 μιτι, more preferably from 0.09 to 0.2 μιτι, and more preferably from 0.1 to 0.18 μιτι, and the diameter D90 is comprised in the range of from 1 .5 to 6 μιτι, preferably from 1 .55 to 5.5 μιτι, more preferably from 1 .6 to 5 μιτι, more preferably from 1 .65 to 4.5 μιτι, and more preferably from 1 .7 to 4.2 μιτι, and more preferably from 2.3 to 3.2 μιτι. According to particularly preferred embodiments of the present invention, the particle size distribution of the mixed oxide particles obtainable from flame spray pyrolysis is such that the average diameter D50 is comprised in the range of from 0.55 to 0.9 μιτι, the diameter D10 is comprised in the range of from 0.1 to 0.18 μιτι, and the diameter D90 is comprised in the range of from 2.3 to 3.2 μιτι.

Therefore, the present invention also relates to mixed oxide particles obtainable from flame spray pyrolysis, wherein the particles comprise ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce, and/or yttria, and wherein the average particle size distribution is such that the average diameter D50 is comprised in the range of from 0.3 to 1.4 μιτι, the diameter D10 is comprised in the range of from 0.01 to 0.28 μιτι, and the diameter D90 is comprised in the range of from 1.5 to 6 μιτι.

According to preferred embodiments of the present invention, the aforementioned mixed oxide particles are obtainable and/or obtained, and preferably obtained according to any of the partic- ular and preferred embodiments of the inventive process as defined in the present application. According to particularly preferred embodiments, the mixed oxide particles are obtainable from flame spray pyrolysis according to the preferred embodiments of the inventive process, wherein said specific pyrolysis method is at least partly applied in step (3) for obtaining mixed oxide particles according to any of the particular or preferred embodiments of the present invention.

As regards the content of the rare earth oxides other than ceria, and/or of yttria, which may be displayed by the mixed oxide particles of the present invention, no particular restriction applies, wherein it is preferred that the content thereof corresponds to the particular and preferred contents obtained in metal oxide particles as obtained from particular and preferred embodiments of the inventive process. Thus, by way of example, the content of the rare earth oxides other than ceria, and/or of yttria in the mixed oxide calculated as their respective oxide is comprised in the range of anywhere from 0.05 to 30 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles. According to the present invention, it is however preferred that the content of the rare oxides other than ceria, and/or of yttria in the mixed oxide calculated as their respective oxides is comprised in the range of from 0.1 to 25 wt.-%, more preferably of from 0.5 to 20 wt.-%, more preferably of from 1 to 15 wt.-%, more preferably of from 2 to 12 wt.-%, more preferably of from 3 to 10 wt.-%, more preferably of from 3.5 to 8 wt.-%, and more preferably of from 4 to 7 wt.-%. According to particularly preferred embodiments of the present invention, the mixed oxide particles contain from 4.5 to 6 wt.-% of the rare earth oxides other than ceria, and/or of yttria calculated as their respective oxides and based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles.

Regarding the one or more oxides of one or more rare earth elements other than ceria which may be comprised in the mixed oxide particles, there is no particular restriction according to the present invention neither with respect to the type nor with respect to the number of the one or more rare earth oxides other than ceria which may be comprised therein. According to the present invention it is however preferred that said one or more rare earth oxides other than ceria comprise one or more of lanthana, praseodymia, and neodymia, including mixtures of two or three thereof, wherein it is further preferred that the one or more rare earth oxides other than ceria comprise lanthana and/or neodymia. According to particularly preferred embodiments of the present invention, the one or more rare earth oxides other than ceria include lanthana, wherein even more preferably the rare earth oxide other than ceria is lanthana.

Therefore, according to preferred embodiments of the mixed oxide particles according to the present invention, the one or more rare earth oxides other than ceria are selected from the group consisting of lanthana, praseodymia, neodymia, and combinations of two or three thereof, wherein the one or more rare earth oxides preferably comprise lanthana and/or neodymia, preferably lanthana, wherein even more preferably the rare earth oxide other than ceria is lanthana.

No particular restriction applies according to the present invention as to the content of ceria and in particular of CeC>2 which may be contained in the mixed oxide particles such that the amount of ceria contained therein may for example range anywhere from 1 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles. According to preferred embodiments of the present invention, the content of ceria and in particular of CeC>2 in the mixed oxide particles is comprised in the range of from 5 to 80 wt.-%, more preferably of from 10 to 70 wt.-%, more preferably of from 20 to 65 wt.-%, more preferably of from 25 to 60 wt.-%, more preferably of from 30 to 55 wt.-%, more preferably of from 35 to 50 wt.-%, and more preferably of from 38 to 48 wt.-%. According to particularly preferred embodiments of the present invention, the content of ceria and in particular of CeC>2 in the mixed oxide particles is comprised in the range of from 40 to 45 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles. As regards the content of ceria in the mixed oxide particles, said content may in principle relate to any form of ceria and in particular to CeC>2, Ce2C>3, and any mixture of said cerium oxides, wherein the content of ceria in the mixed oxide particles of the present invention preferably refer to the cerium (IV) oxide CeC>2.

According to alternatively preferred embodiments of the present invention, and in particular relative to embodiments of the mixed oxide particles for use in oxidative applications, in particular in the field of automotive exhaust gas treatment, and even more particularly as oxidation catalyst and preferably for use in diesel oxidation catalysts (DOC), the content of ceria and in particular of CeC>2 in the mixed oxide particles is comprised in the range of from 5 to 99 wt.-% based on the total weight of the one or more rare earth oxides, zirconia and optional yttria contained in the mixed oxide particles, preferably from 15 to 98 wt.-%, more preferably from 30 to 95 wt.-%, more preferably from 40 to 90 wt.-%, and more preferably from 45 to 87 wt.-%. According to said alternatively preferred embodiments of the present invention, it is particularly preferred that the content of ceria in the mixed oxide particles and in particular of CeC>2 is comprised in the range of from 50 to 80 wt.-%.

According to a further alternative embodiment of the present invention which is also preferred, and in particular to embodiments of the mixed oxide particles for use as oxygen storage components in the field of automotive exhaust gas treatment and in particular for use as an oxygen storage component in three-way catalysts (TWC), the content of ceria and in particular of CeC>2 in the mixed oxide particles is comprised in the range of from 1 to 80 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, more preferably from 5 to 70 wt.-%, more preferably from 10 to 60 wt.-%, more preferably from 15 to 55 wt.-%, and more preferably from 18 to 50 wt.-%. According to particularly preferred embodiments of said alternative embodiments, the content of ceria and in par- ticular of CeC>2 in the mixed oxide particles is comprised in the range of from 20 to 45 wt.-%.

As regards the content of zirconia in the mixed oxide particles, as for ceria, there is no particular restriction in this respect provided that a mixed oxide particle according to any of the particular or preferred embodiments of the present invention is provided. Thus, by way of example, the content of zirconia in the mixed oxide particles is comprised in the range of anywhere from 1 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles. According to the present invention, it is, however, preferred that zirconia is contained in the mixed oxide particles in an amount comprised in the range of from 5 to 90 wt.-%, and more preferably of from 10 to 80 wt.-%, more preferably of from 30 to 70 wt.-%, more preferably of from 40 to 65 wt.-%, more preferably of from 43 to 60 wt.-% , and more preferably of from 45 to 57 wt.-%. According to particularly preferred embodiments of the present invention, the content of zirconia in the mixed oxide particles is comprised in the range of from 46 to 55 wt.-%. According to alternatively preferred embodiments of the present invention, and in particular relative to embodiments of the mixed oxide particles for use in oxidative applications, in particular in the field of automotive exhaust gas treatment, and even more particularly as oxidation catalyst and preferably for use in diesel oxidation catalysts (DOC), the content of zirconia in the mixed oxide particles is comprised in the range of from 0.5 to 80 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, wherein more preferably the content of zirconia in the mixed oxide particles is comprised in the range of from 1 to 70 wt.-%, more preferably of from 5 to 60 wt.-%, more preferably of from 10 to 55 wt.-%, and more preferably of from 13 to 50 wt.-%. According to particularly preferred embodiments of said alternative embodiments, the content of zirconia in the mixed oxide particles is comprised in the range of from 15 to 45 wt.-%. Concerning the further composition of the mixed oxide particles according to any of the particular and preferred embodiments, there is also no particular restriction which would apply relative to any further compounds which may be contained therein. It is, however, preferred according to the present invention that the mixed oxide particles further comprise one or more transition metals. As regards the form in which the one or more transition metals may be provided in the mixed oxide particles, no particular restrictions apply such that these may be provided in the mixed oxid particles for example via impregnation of the one or more metals or one or more compounds containing the one or more metals, and preferably one or more transition metal salts. According to particularly preferred embodiments of the present invention, however, said one or more transition metals are solid-solutionized in the mixed oxide particles together with ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce, and/or yttria contained therein. According to particularly preferred embodiments, the one or more transition metals includes one or more platinum group metals, wherein the one or more platinum group metals are preferably selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, and mixtures of two or more thereof, and more preferably from the group consisting of Rh, Pd, Pt, and mixtures of two or more thereof. According to particularly preferred embodiments of the present invention, the mixed oxide particles further comprise Pd and/or Pt, and preferably Pd, in addition to ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce, and/or yttria. Therefore, embodiments of the present invention are preferred, wherein the mixed oxide particles comprise one or more transition metals and preferably one or more platinum group metals, more preferably one or more platinum group metals selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, and mixtures of two or more thereof, more preferably from the group consisting of Rh, Pd, Pt, and mixtures of two or more thereof, wherein more preferably the platinum group metal is Pd and/or Pt, preferably Pd.

Regarding the preferred embodiments of the inventive mixed oxide particles, wherein one or more transition metals and in particular one or more platinum group metals is further contained therein, there is in principle no particular restriction as to the amounts in which said one or more metals may be contained therein as further component. Thus, by way of example, the one or more transition metals and in particular the one or more platinum group metals may be further comprised in the mixed oxide particles in an amount ranging anywhere from 0.01 to 30 wt.-% calculated as the metal and based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, wherein preferably the amount thereof is comprised in the range of from 0.05 to 20 wt.-%, more preferably of from 0.1 to 15 wt- %, more preferably of from 0.5 to 7 wt.-%, more preferably of from 1 to 5 wt.-%, and more preferably of from 2 to 4 wt.-%. According to further alternative embodiments of the present invention which are particularly preferred, and in particular to embodiments of the mixed oxide particles for use as oxygen storage components in the field of automotive exhaust gas treatment and in particular for use as an ox- ygen storage component in three-way catalysts (TWC), the content of zirconia in the mixed oxide particles is comprised in the range of from 5 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, wherein more preferably the content of zirconia is comprised in the range of from 15 to 90 wt.-% and more preferably of from 30 to 85 wt.-%, more preferably of from 40 to 80 wt.-% and more preferably of from 45 to 77 wt.-%. According to said alternatively preferred embodiments, it is particularly preferred that the content of zirconia in the mixed oxide particles is comprised in the range of from 50 to 75 wt.-%.

As regards the surface area of the mixed oxide particles according to the present invention, there is no particular restriction as to the surface area which the mixed oxide particles may display such that surface areas and in particular surface areas determined according to the BET method, may be comprised in the range of anywhere from 0.5 to 150 m²/g, wherein preferably surface areas and in particular BET surface areas ranging from 1 to 100 m²/g are preferred, and more preferably from 2 to 70 m²/g, more preferably of from 5 to 50 m²/g, and more preferably of from 10 to 40 m²/g. According to particularly preferred embodiments of the present invention, the surface area and in particular the BET surface area of the mixed oxide particles is comprised in the range of from 15 to 35 m²/g.

Regarding the preferred surface areas of the mixed oxide particles according to the present invention, it is noted that said preferred and particularly preferred values relate in particular to embodiments of the mixed oxide particles for use as an oxidation catalyst in the treatment of automotive exhaust gases and in particular for use in diesel oxidation catalysts. According to alternatively preferred embodiments of the present invention, the mixed oxide particles display a surface area and in particular a BET surface area comprised in the range of from 20 to 100 m²/g, and more preferably of from 30 to 90 m²/g, more preferably of from 40 to 85 m²/g, and more preferably of from 45 to 80 m²/g. According to said alternatively preferred embodiments, it is particularly preferred that the surface area and in particular the BET surface area of the mixed oxide particles is comprised in the range of from 50 to 75 m²/g. As regards said alternatively preferred embodiments of the mixed oxide particles according to the present invention, it is not- ed that said embodiments are particularly adapted for use as oxygen storage components in exhaust gas treatment applications and in particular for use as an oxygen storage component in three-way catalysts.

With respect to the BET surface area as defined in the present invention, it is noted that this refers in particular to the BET surface area determined according to DIN 66131 , and preferably to the BET surface area determined by absorption and desorption of nitrogen gas at 77 K according to DIN 66131 . Concerning the ageing behavior of the mixed oxide particles of the present invention, it is preferred that these display a high stability both relative to the performance of the mixed oxide particles in particular as an oxygen storage component as well as with respect to the physical properties thereof. Thus, according to preferred embodiments of the inventive process, the BET surface area of the mixed oxide particles after ageing thereof is preferably comprised in the range of from 0.5 to 50 m²/g and more preferably in the range of from 1 to 20 m²/g, and more preferably of from 1 to 15 m²/g. According to particularly preferred embodiments of the present invention, the mixed oxide particles display a BET surface area ranging from 1 to 8 m²/g after ageing thereof. As regards the term "ageing" as employed in the present application, this preferably designates a treatment of the mixed oxide particles according to any of the particular and preferred embodiments of the present invention in air containing 10 vol.-% of H2O at a temperature of 1 ,100°C for 40 hours. Thus, it is particularly preferred that the mixed oxide particles according to the present invention display a relative stable BET surface area under ageing condition such that the reduction in said BET surface area after ageing calculated as the difference between the BET surface area values in the fresh and aged states divided by the BET surface area of the fresh material prior to ageing ( = [BET fresh - BET aged] / BET fresh) is comprised in the range of from 40 to 90 %, and preferably in the range of from 40 to 80 %. According to particularly preferred embodiments of the present invention, the reduction in BET surface area after ageing of the mixed oxide material according to the present invention as calculated in the aforementioned fashion lies between 40 and 60 %. Concerning the dimensions of the mixed oxide particles according to the present invention, in principle these may adopt any conceivable values. According to the present invention, it is, however, preferred that the mixed oxide particles are microcrystalline, wherein it is preferred that the average particle size of the mixed oxide particles is comprised in the range of from 1 to 150 nm, and preferably of from 5 to 100 nm, and preferably of from 6 to 50 nm, more preferably of from 7 to 30 nm, more preferably of from 8 to 20 nm, more preferably of from 9 to 18 nm, and more preferably of from 10 to 16 nm. According to particularly preferred embodiments of the present invention, the mixed oxide particles display an average particle size comprised in the range of from 1 1 to 15 nm. As regards the values of the average particle size as defined in the present application, these refer in particular to the average particle size of the mixed oxide par- tides as obtained using the Scherrer formula as follows:

ϋ cos Θ wherein K is the shape factor, lambda (λ) is the X-ray wave length, beta (β) is the line broaden- ing at half the maximum intensity (FWHM) in radians, and theta (0) is the Bragg angle. As regards tao (τ), this stands for the mean size of the ordered (crystalline) domains, which may be smaller or equal to the grain size. The dimensionless shape factor has a typical value of about

0.9. and may be adapted to the actual shape of the crystallite if necessary.

Regarding the use of the mixed oxide particles according to the present invention, there is no restriction whatsoever as to the applications or methods in which the inventive materials may be used. According to preferred embodiments of the present invention, however, the mixed oxide particles are used as a catalyst and/or as a catalyst support. Alternatively, the mixed oxide particles are preferably used as an oxygen storage component involving the reversible uptake of oxygen, wherein preferably the application as an oxygen storage component relates to a partic- ular use of the inventive materials in catalytic applications either as a catalyst and/or as a catalyst support. Thus, according to particularly preferred embodiments of the present invention, the mixed oxide particles according to any of the particular or preferred embodiments of the present invention are employed as an oxygen storage component and/or as a catalyst or catalyst component. Regarding said preferred uses, there is again principally no restriction whatsoever as to the specific applications and/or methods in which the inventive materials may act as an oxygen storage component and/or as a catalyst or catalyst component, wherein it is preferred that the inventive materials are used as such in catalysts for the treatment of exhaust gas and, in particular, in the treatment of automotive exhaust gas. According to said preferred embodiments, it is yet further preferred that the inventive materials are used as an oxygen storage component and/or as a catalyst or catalyst component in a three way catalyst and/or in a diesel oxidation catalyst.

Therefore, the present invention further relates to the use of mixed oxide particles according to any of the particular or preferred embodiments as defined in the present application as an oxy- gen storage component, a catalyst and/or as a catalyst support, preferably as an oxygen storage component and/or as a catalyst or catalyst component in a three way catalyst and/or diesel oxidation catalyst for the treatment of exhaust gas, preferably of automotive exhaust gas.

The present invention includes the following embodiments, wherein these include the specific combinations of embodiments as indicated by the respective interdependencies defined therein:

1. A process for the production of mixed oxide particles comprising:

(2) forming an aerosol of the dispersion provided in step (1 ); and

(3) pyrolyzing the aerosol of step (2) to obtain mixed oxide particles.

2. The process of embodiment 1 , wherein the disperse phase comprises a hydrophilic sol- vent system, the hydrophilic solvent system preferably comprising one or more hydrophilic solvents, wherein the one or more hydrophilic solvents are preferably selected from the group of polar solvents, more preferably from the group of polar protic and polar aprotic solvents, including mixtures of two or more thereof, and more preferably from the group consisting of

alcohols, diols, polyols, ethers, carboxylic acids, formamides, nitriles, sulfoxides, esters of carboxylic acids, ketones, lactones, lactames, sulfones, nitro-compounds, alkyl derivates of urea-compounds, water, and mixtures of two or more thereof, more preferably from the group consisting of (Ci-Cs)alcohols, (C2-C6)diols, (Ci-C3)dialkylethers, (Ci-Cs)carboxylic acids, alkyl amides, acetonitrile, dimethylsulfoxide, propylene carbonate, (C2-C6)ketones, (C4-C7)lactones, (C4-C7)lactames, nitromethane, sulfolane, 1 ,3 dimethyl-3,4,5,6- tetrahydro2(1 H)pyrimidinon (tetra methyl urea), dimethylcarbonate, ethylene carbonate, propylene carbonate, water, and combinations of two or more thereof, more preferably from the group consisting of (C2-C4)alcohols, (C2-C4)diols, (C2-C4)ketones, (Ci- C2)dialkylethers, (C2-C4)carboxylic acids, dimethylformamide, acetonitrile, dimethylsulfoxide, water, and combinations of two or more thereof, more preferably from the group consisting of ethanol, methanol, ethylene glycol, dimethylether, ethylmethylether, acetic acid, acetonitrile, water, and combinations of two or more thereof, more preferably from the group consisting of ethanol, methanol, ethylene glycol, dimethylether, acetonitrile, water, and combinations of two or more thereof, more preferably from the group consisting of methanol, acetonitrile, water, and combinations of two or more thereof, wherein even more preferably the hydrophilic solvent system comprises methanol and/or water, preferably water.

The process of embodiment 2, wherein the hydrophilic solvent system is comprised in droplets, wherein the droplets are preferably stabilized by one or more emulsifying agents.

The process of any of embodiments 1 to 3, wherein the continuous phase comprises a hydrophobic solvent system, the hydrophobic solvent system preferably comprising one or more hydrophobic solvents, wherein the one or more hydrophobic solvents are preferably selected from the group consisting of aliphatic and aromatic hydrocarbons, heterocyclic compounds, and mixtures of two or more thereof, more preferably from the group consisting of aliphatic and aromatic hydrocarbons, wherein even more preferably the one or more hydrophobic solvents comprise one or more aliphatic hydrocarbons.

The process of embodiment 4, wherein the group of aliphatic hydrocarbons comprises one or more selected from branched and/or unbranched, preferably unbranched aliphatic (C4-Ci2)hydrocarbons, including mixtures of two or more thereof, preferably aliphatic (C5- Cio)hydrocarbons, more preferably aliphatic (C6-C8)hydrocarbons, more preferably aliphatic (C6-C7)hydrocarbons, and even more preferably one or more selected from branched and/or unbranched, preferably unbranched aliphatic C6-hydrocarbons, wherein even more preferably the group of aliphatic hydrocarbons comprises one or more selected from pen- tane, hexane, heptane, octane, and mixtures of two or more thereof, wherein even more preferably the aliphatic hydrocarbons comprise pentane and/or hexane, preferably hex- ane.

The process of embodiment 4 or 5, wherein the group of aromatic hydrocarbons comprises one or more selected from aromatic (C6-Ci2)hydrocarbons, including mixtures of two or more thereof, preferably aromatic (C7-Cn)hydrocarbons, more preferably aromatic (Cs- Cio)hydrocarbons, more preferably aromatic (Cs-C^hydrocarbons, and even more preferably aromatic Cs-hydrocarbons, wherein even more preferably the group of aromatic hydrocarbons comprises one or more selected from toluene, ethylbenzene, xylene, mesity- lene, durene, and mixtures of two or more thereof, more preferably from toluene, ethylbenzene, xylene, and mixtures of two or more thereof, and wherein even more preferably the aromatic hydrocarbons comprise toluene and/or xylene, preferably xylene.

The process of any of embodiments 4 to 6, wherein the group of heterocyclic compounds comprises one or more selected from N- and O-containing heterocycles, including mixtures of two or more thereof, more preferably one or more selected from pyrrolidine, pyrrole, pipehdine, pyridine, azepane, azepine, tetrahydrofurane, and mixtures of two or more thereof.

The process of any of embodiments 1 to 7, wherein the dispersion provided in step (1 ) is formed by a process comprising:

(1.b) providing a hydrophobic solvent system optionally comprising one or more emulsifying agents;

(1.c) dispersing the solution in the hydrophobic solvent system by mixing, preferably by emulsification, for forming a dispersion.

The process of embodiment 8, wherein mixing in step (1 .c) is achieved by use of a ho- mogenizer, preferably with a rotor-stator homogenizer, with an ultrasonic homogenizer, with a high pressure homogenizer, by microfluidic systems, or by membrane emulsification, more preferably with a high pressure homogenizer or with a rotor-stator homogenizer, and more preferably with a rotor-stator homogenizer. The process of any of embodiments 3 to 9, wherein the one or more emulsifying agents being selected from the group consisting of ionic and nonionic surfactants, including mixtures thereof, preferably from the group consisting of nonionic surfactants. The process of embodiment 10, wherein the ionic surfactants comprise one or more anionic surfactants, preferably one or more anionic surfactants selected from the group consisting of salts of (C6-Cis)sulfate, (C6-Cis)ethersulfate, (C6-Ci8)sulfonate, (C6- Ci8)sulfosuccinate (C6-Cis)phosphate, (C6-Cis)carboxylate, and mixtures of two or more thereof, more preferably from the group consisting of salts of (C8-Ci6)sulfate, (Cs-

Ci6)ethersulfate, (C8-Ci6)sulfonate, (C8-Ci6)sulfosuccinate, (C8-Ci6)phosphate, (Cs- Ci6)carboxylate, and mixtures of two or more thereof, more preferably from the group consisting of salts of (Cio-Ci4)sulfate, (Cio-Ci4)ethersulfate, (Cio-Ci4)sulfonate, (Cs- Ci4)sulfosuccinate, (Cio-Ci4)phosphate, (Cio-Ci4)carboxylate, and mixtures of two or more thereof, more preferably from the group consisting of salts of laurylsulfate, laurylsulfonate, dioctyl sulfosuccinate, laurylphosphate, laurate, and mixtures of two or more thereof, wherein the counterion is preferably selected from the group consisting of H⁺, alkali metals, alkaline earth metals, ammonium, and combinations of two or more thereof, more preferably from the group consisting of H⁺, Li⁺, Na⁺, K⁺, ammonium, and combinations of two or more thereof, more preferably from the group consisting of Na⁺, K⁺, ammonium, and combinations of two or more thereof, wherein even more preferably the counterion is Na⁺ and/or ammonium, preferably Na⁺. The process of embodiment 10 or 1 1 , wherein the ionic surfactants comprise one or more cationic surfactants, preferably one or more cationic surfactants selected from the group consisting of primary, secondary, tertiary, and quaternary ammonium compounds, including mixtures of two or more thereof, wherein more preferably the cationic surfactants comprise one or more quaternary ammonium compounds, preferably selected from the group consisting of salts of (C8-Ci8)trimethylammonium, (C8-Ci8)pyridinium, benzalkoni- um, benzethonium, dimethyldioctadecylammonium, cetrimonium, dioctadecyldime- thylammonium, and mixtures of two or more thereof, more preferably from the group consisting of salts of cetyltrimethylammonium, dodecyltrimethylammonium, cetylpyridinium, benzalkonium, benzethonium, dimethyldioctadecylammonium, cetrimonium, dioctadecyl- dimethylammonium, wherein the counterion is preferably selected from the group consisting of halides, carbonates, hydroxide, nitrate, phosphate, sulfate, and combinations of two or more thereof, more preferably from the group consisting of chloride, fluoride, bromide, hydrogen carbonate, hydroxide, nitrate, sulfate, and combinations of two or more thereof, wherein more preferably the counterion is chloride and/or nitrate, preferably chloride. The process of any of embodiments 10 to 12, wherein the ionic surfactants comprise one or more zwitterionic surfactants, preferably one or more betaines, wherein more preferably the ionic surfactants comprise cocamidopropylbetaine or alkyldimethylaminoxide. The process of any of embodiments 10 to 13, wherein the nonionic surfactants are selected from the group consisting of (C8-C22)alcohols, (C6-C2o)alcohol ethoxylates with 1 to 8 ethylene oxide units, (C6-C2o)alkyl polyglycosides, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, glucoside alkyl ethers, polyoxyethylene glycol al- kylphenol ethers, glycerol alkyl esters, sorbitan alkyl esters, polyoxyethylene glycol sorbi- tan alkyl esters, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, poly- ethoxylated tallow amine, and mixtures of two or more thereof,

wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci4-C2o)alcohols, (Cs-Cisjalcohol ethoxylates with 2 to 6 ethylene oxide units, (Cs-Ci8)alkyl polyglycosides, octaethylene glycol monododecyl ether and/or pen- taethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl gluco- side, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol octylphe- nol ethers, preferably triton X-100, nonoxynol-9, glyceryl laurate, polyglycerol polyricinole- ate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof,

wherein more preferably the one or more nonionic surfactants are selected from the group consisting of (Ci6-Ci8)alcohols, (Ci6-Ci8)alcohol ethoxylates with 2 to 6 ethylene ox- ide units, (Cs-Ci4)alkyl polyglycosides, preferably cetyl alcohol, stearyl alcohol, oleyl alcohol, and mixtures of two or more thereof, octaethylene glycol monododecyl ether and/or pentaethylene glycol monododecyl ether, polyoxypropylene glycol alkyl ethers, decyl glucoside, lauryl glucoside, myristil glucoside, octyl glucoside, polyoxyethylene glycol oc- tylphenol ethers, nonoxynol-9, glyceryl laurate, polyglycerol polyricinoleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan oleate, polyoxyethylene (20) sorbitan monolaurate, polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (20) sorbitan monostearate, polyoxyethylene (20) sorbitan monooleate, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, Stearyl-EC>2, polyglyceryl-2-dipolyhydroxystearate, polyglyceryl-distearate, C13/15 -

PEG₃, C13 - PEG₂, glyceryl monooleate, C16/18 - PEG₂, oleyl - PEG₂, PEG₂₀ - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEGg, and mixtures of two or more thereof,

more preferably from the group consisting of polyglyceryl-2-dipolyhydroxystearate, diglyc- eryl-distearate, triglyceryl-distearate, C13/15 - PEG3, C13 - PEG₂, glyceryl monooleate, sorbitan monooleate, polyglycerol-3-polyricinoleate, C16/18 - PEG₂, oleyl - PEG₂, PEG₂₀ - sorbitan monooleate, functionalized polyisobutene, C16/18 - PEGg, and mixtures of two or more thereof,

more preferably from the group consisting of polyglyceryl-2-dipolyhydroxystearate, diglyc- eryl-distearate, triglyceryl-distearate, and mixtures of two or more thereof,

wherein it is even more preferred that the nonionic surfactant comprises polyglycerol-3- polyricinoleate. The process of any of embodiments 3 to 14, wherein the one or more emulsifying agent is contained in the dispersion in an amount of from 0.01 to 20 wt.-% based on the total weight of the dispersion provided in step (1 ), preferably from 0.05 to 10 wt.-%, more preferably from 0.1 to 7.0 wt.-%, more preferably from 0.5 to 5.0 wt.-%, more preferably from 0.8 to 4.0 wt.-%, more preferably from 1 to 3.0 wt.-%, more preferably from 1 .3 to 2.5 wt.- %, more preferably from 1 .5 to 2.0 wt.-%, and even more preferably from 1.7 to 1.9 wt.-%.

The process of any of embodiments 1 to 15, wherein the average particle size D50 of the disperse phase is comprised in the range of from 0.05 to 20 μιτι, preferably from 0.1 to 15 μιτι, more preferably from 0.2 to 10 μιτι, more preferably from 0.5 to 9 μιτι, more preferably from 1 to 5 μιτι, and more preferably from 2 to 4 μιτι.

17. The process of any of embodiments 1 to 16, wherein the particle size D90 of the disperse phase is comprised in the range of from 0.1 to 50 μιτι, preferably from 0.5 to 30 μιτι, more preferably from 1 to 22 μιτι, more preferably from 2 to 16 μιτι, more preferably from 3 to 8 μιτι, and more preferably from 4 to 6 μιτι.

The process of any of embodiments 1 to 17, wherein the one or more rare earth oxides other than ceria is selected from the group consisting of lanthana, praseodymia, neo- dymia, and mixtures of two or three thereof, wherein the one or more rare earth oxides preferably comprises lanthana and/or neodymia, preferably lanthana, wherein even more preferably the rare earth oxide other than ceria is lanthana. 19. The process of any of embodiments 1 to 18, wherein the concentration of the one or more precursor compounds of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria calculated as their respective oxides contained in the dispersion provided in step (1 ) is comprised in the range of from to 0.01 to 5 wt.-% based on the total weight of the dispersion provided in step (1 ), preferably of from 0.05 to 2 wt.-%, more preferably of from 0.08 to 1 wt.-%, more preferably of from 0.1 to 0.5 wt.-%, more preferably of from 0.15 to 0.35 wt.-%, more preferably of from 0.18 to 0.3 wt.-%, and even more preferably of from 0.21 to 0.27 wt.-%.

The process of any of embodiments 1 to 19, wherein the concentration of the one or more precursor compounds of ceria calculated as CeC>2 contained in the dispersion provided in step (1 ) is comprised in the range of from 0.05 to 15 wt.-% based on the total weight of the dispersion provided in step (1 ), preferably of from 0.1 to 10 wt.-%, more preferably of from 0.5 to 5 wt.-%, more preferably of from 0.8 to 3 wt.-%, more preferably of from 1 to 2.5 wt.- %, more preferably of from 1.4 to 2.2 wt.-%, and even more preferably of from 1.7 to 2.0 wt.-%. The process of any of embodiments 1 to 20, wherein the concentration of the one or more precursor compounds of zirconia calculated as ZrC>2 contained in the dispersion provided in step (1 ) is comprised in the range of from 0.05 to 15 wt.-% based on the total weight of the dispersion provided in step (1 ), preferably of from 0.1 to 10 wt.-%, more preferably of from 0.5 to 7 wt.-%, more preferably of from 1 to 5 wt.-%, more preferably of from 1 .5 to 4 wt.-%, more preferably of from 1.8 to 3 wt.-%, and even more preferably of from 2.1 to 2.3 wt.-%.

The process of any of embodiments 1 to 21 , wherein the concentration of the disperse phase in the dispersion provided in step (1 ) is comprised in the range of from 1 to 80 wt- % based on the total weight of the dispersion, preferably from 5 to 70 wt.-%, more preferably from 10 to 60 wt.-%, more preferably from 20 to 55 wt.-%, more preferably from 30 to 50 wt.-%, more preferably from 35 to 45 wt.-%, and more preferably from 40 to 42 wt.-%.

The process of any of embodiments 1 to 22, wherein the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprise one or more salts, preferably one or more salts selected from the group consisting of nitrates, halides, sulfates, phosphates, carbonates, hydroxides, carboxylates, alcoholates, and mixtures of two or more thereof,

more preferably from the group consisting of nitrates, fluorides, chlorides, bromides, hydrogensulfates, hydrogenphosphates, dihydrogenphosphates, hydrogencarbonates, hydroxides, (C6-Cio)carboxylates, (C2-C5) alcoholates, and mixtures of two or more thereof,

more preferably from the group consisting of nitrates, chlorides, bromides, hydrogensulfates, dihydrogenphosphates, hydroxides, (C7-Cg)carboxylates, (C3-C4) alcoholates, and mixtures of two or more thereof,

more preferably from the group consisting of nitrates, chlorides, hydrogensulfates, hydroxides, Cs-carboxylates, C3-alcoholates, and mixtures of two or more thereof,

wherein more preferably the salts are selected from nitrates and/or chlorides, wherein even more preferably the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprise one or more nitrates. 24. The process of any of embodiments 1 to 23, wherein the dispersion provided in step (1 ) further comprises one or more platinum group metals, preferably one or more platinum group metals selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, and mixtures of two or more thereof, more preferably from the group consisting of Rh, Pd, Pt, and mixtures of two or more thereof, wherein more preferably the platinum group metal is Pd and/or Pt, preferably Pd. 25. The process of embodiment 24, wherein the dispersion provided in step (1 ) comprises the one or more platinum group metals in an amount ranging from 0.001 to 5 wt.-% calculated as the metal based on the total weight of the dispersion provided in step (1 ), preferably from 0.003 to 2 wt.-%, more preferably from 0.005 to 1 wt.-%, more preferably from 0.008 to 0.5 wt.-%, more preferably from 0.01 to 0.3wt.-%, more preferably from 0.03 to 0.2 wt-

%, and even more preferably from 0.05 to 0.15 wt.-%.

26. The process of any of embodiments 1 to 25, wherein pyrolysis in step (3) is performed in an atmosphere containing oxygen, preferably in air, more preferably in air enriched with oxygen, and even more preferably in an oxygen atmosphere. 27. The process of any of embodiments 1 to 26, wherein pyrolysis in step (3) is performed at a temperature comprised in the range of from 800 to 4,000°C, preferably of from 900 to 3,500°C, more preferably of from 1 ,000 to 3,000°C, more preferably of from 1 ,100 to 2,500°C, and even more preferably of from 1 ,150 to 2,000°C, and even more preferably of from 1 ,200 to 1 ,500°C. 28. Mixed oxide particles obtainable and/or obtained, preferably obtained by a process according to any of embodiments 1 to 27.

29. Mixed oxide particles obtainable from flame spray pyrolysis, preferably by a process according to any of embodiments 1 to 27, wherein the particles comprise ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce, and/or yttria, and wherein the average particle size distribution is such that

the average diameter D50 is comprised in the range of from 0.3 to 1.4 μιτι, preferably from 0.35 to 1.35 μιτι, more preferably from 0.4 to 1 .3 μιτι, more preferably from 0.45 to 1 .25 μιτι, more preferably from 0.5 to 1.2 μιτι, and more preferably from 0.55 to 0.9 μιτι, and

the diameter D10 is comprised in the range of from 0.01 to 0.28 μιτι, preferably from

0.04 to 0.26 μιτι, more preferably from 0.06 to 0.24 μιτι, more preferably from 0.08 to 0.22 μιτι, more preferably from 0.09 to 0.2 μιτι, and more preferably from 0.1 to 0.18 μιτι, and the diameter D90 is comprised in the range of from 1.5 to 6 μιτι, preferably from 1 .55 to 5.5 μιτι, more preferably from 1 .6 to 5 μιτι, more preferably from 1.65 to 4.5 μιτι, more preferably from 1.7 to 4.2 μιτι, and more preferably from 2.3 to 3.2 μιτι.

30. The mixed oxide particles of embodiment 29, wherein the average size of the primary particles of the mixed oxide particles is comprised in the range of from 1 to 150 nm, preferably from 5 to 100 nm, more preferably of from 6 to 50 nm, more preferably of from 7 to 30 nm, more preferably of from 8 to 20 nm, more preferably of from 9 to 18 nm, more preferably of from 10 to 16 nm, and even more preferably of from 1 1 to 15 nm, wherein preferably the average size of the primary particles is obtained using the Scherrer formula.

The mixed oxide particles of embodiment 29 or 30, wherein the content of the rare earth oxides other than ceria, and/or of yttria in the mixed oxide calculated as their respective oxides is comprised in the range of from 0.05 to 30 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, preferably of from 0.1 to 25 wt.-%, more preferably of from 0.5 to 20 wt.-%, more preferably of from 1 to 15 wt.-%, more preferably of from 2 to 12 wt.-%, more preferably of from 3 to 10 wt.-%, more preferably of from 3.5 to 8 wt.-%, more preferably of from 4 to 7 wt.-%, more preferably of from 4.5 to 6 wt.-%, and even more preferably from 4.5 to 4.9 wt.-%.

The mixed oxide particles of any of embodiments 29 to 31 , wherein the one or more rare earth oxides other than ceria are selected from the group consisting of lanthana, praseo- dymia, neodymia, and mixtures of two or three thereof, wherein the one or more rare earth oxides preferably comprise lanthana and/or neodymia, preferably lanthana, wherein even more preferably the rare earth oxide other than ceria is lanthana.

The mixed oxide particles of any of embodiments 29 to 32, wherein the content of ceria in the mixed oxide particles is comprised in the range of from 0.5 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, preferably from 1 to 90 wt.-%, more preferably from 5 to 80 wt- %, more preferably from 10 to 70 wt.-%, more preferably from 20 to 65 wt.-%, more preferably from 25 to 60 wt.-%, more preferably from 30 to 55 wt.-%, more preferably from 35 to 50 wt.-%, more preferably from 38 to 48 wt.-%, more preferably from 40 to 45 wt.-%.

The mixed oxide particles of any of embodiments 29 to 33, wherein the content of ZrC>2 in the mixed oxide particles is comprised in the range of from 1 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, preferably from 5 to 90 wt.-%, more preferably from 10 to 80 wt.-%, more preferably from 30 to 70 wt.-%, more preferably from 40 to 65 wt.-%, more preferably from 43 to 60 wt.-%, more preferably from 45 to 57 wt.-%, more preferably from 46 to 55 wt.-%.

The mixed oxide particles of any of embodiments 29 to 34, wherein the mixed oxide particles comprise one or more transition metals and preferably one or more platinum group metals, more preferably one or more platinum group metals selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, and mixtures of two or more thereof, more preferably from the group consisting of Rh, Pd, Pt, and mixtures of two or more thereof, wherein more preferably the platinum group metal is Pd and/or Pt, preferably Pd.

36. The mixed oxide particles of embodiment 35, wherein the mixed oxide particles comprise the one or more transition metals and preferably the one or more platinum group metals in an amount ranging from 0.01 to 30 wt.-% calculated as the metal and based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles, preferably in an amount ranging from 0.05 to 20 wt.-%, more preferably from 0.1 to 15 wt.-%, more preferably from 0.3 to 10 wt.-%, more preferably from 0.5 to 7 wt.-%, more preferably from 1 to 5 wt.-%, and more preferably from 2 to 4 wt.-%. 37. The mixed oxide particles of any of embodiments 29 to 36, wherein the BET surface area of the mixed oxide particles is comprised in the range of from 0.5 to 150 m²/g, more preferably of from 1 to 100 m²/g, more preferably of from 2 to 70 m²/g, more preferably of from 5 to 50 m²/g, more preferably of from 10 to 40 m²/g, and even more preferably of from 15 to 35 m²/g. 38. Use of mixed oxide particles according to any of embodiments 28 to 37 as an oxygen storage component, a catalyst and/or as a catalyst support, preferably as an oxygen storage component and/or as a catalyst or catalyst component in a three way catalyst and/or diesel oxidation catalyst for the treatment of exhaust gas, preferably of automotive exhaust gas.

DESCRPTION OF THE FIGURES

Figure 1 displays the burner configuration (top and side view) of the apparatus for flame spray pyrolysis used for the examples.

EXAMPLES Reference Example 1

68.2 g of Ce(N0₃)3 · x H₂0 (x ~ 3; m_w = 385,9 g/mol), 77.4 g of ZrO(N0₃)₂ · xH₂0 (x ~ 4; m_w = 304,6 g/mol), and 9.0 g of La(N0₃)3 · x H₂0 (x ~ 2; m_w = 360,8 g/mol) were dissolved in 445.4 g of distilled water. Seperately, 26.3 g of polyglycerol polyricinoleate (Palsgaard® PGPR 4150) were dissolved in 873.7 g of xylene. The solutions were then united and an emulsion with a 40 wt.-% disperse phase was prepared by homogenization of the mixture using an Ultra-Turrax® T25 (IKA®) for 5 min at 12,500 rpm. The D50 and D90 values for the droplet size of the resulting emulsion are respectively displayed in Table 1.

Reference Example 2

The procedure of Example 1 was repeated, wherein an emulsion with slightly larger droplet sizes was obtained as may be taken from the values for the droplet size distribution displayed in Table 1. Reference Example 3

56.6 g of Ce(N0₃)3 · x H₂0 (x ~ 3; m_w = 385,9 g/mol), 85.9 g of ZrO(N0₃)₂ · xH₂0 (x ~ 4; m_w = 304,6 g/mol), and 7.0 g of La(N0₃)3 · x H₂0 (x ~ 2; m_w = 360,8 g/mol) were dissolved in 410.5 g of distilled water. Seperately, 24.5 g of polyglycerol polyricinoleate (Palsgaard® PGPR 4150) were dissolved in 873.7 g of xylene. The solutions were then united and an emulsion with a 40 wt.-% disperse phase was prepared by homogenization of the mixture using an Ultra-Turrax® T25 (IKA®) for 5 min at 12,500 rpm. The droplet size distribution of the resulting emulsion is displayed in Table 1. Reference Example 4

The procedure of Example 3 was repeated. The values for the droplet size distribution in the resulting emulsion are displayed in Table 1. Reference Example 5

The procedure of Example 3 was repeated, wherein the emulsion was prepared by homogenization of the mixture for 5 min at 5,000 rpm. The values for the droplet size distribution in the resulting emulsion are displayed in Table 1.

Reference Example 6

The procedure of Example 3 was repeated, wherein the emulsion was prepared by homogenization of the mixture for 5 min at 25000 rpm. The values for the droplet size distribution in the resulting emulsion are displayed in Table 1.

Reference Example 7

The procedure of Example 3 was repeated, wherein the emulsion was prepared by homogeni- zation of the mixture using a high pressure homogenizer (Microfluidizer M 1 10Y from Microfluid- ics including an interaction chamber having a twin orifice with 0.2 mm and 0.4 mm openings, wherein the orifices are arranged in sequence to one another) operating at a pressure of 400 bar. The values for the droplet size distribution in the resulting emulsion are again displayed in Table 1.

Comparative Example 1

41.4 g of zirconium propylate (70% in propanol), 76.9 g of cerium(lll)-2-ethyl hexanoate in (49% in 2-ethyl hexanoic acid), and 46.9 g of lanthanum(lll)-2-ethyl hexanoate (10% in hexane) were dissolved in 532.1 g of xylene. Comparative Example 2

39.2 g of zirconium propylate (70% in propanol), 61 .97 g of cerium(lll)-2-ethyl hexanoate in (49% in 2-ethyl hexanoic acid), 16 g of lanthanum(lll)-2-ethyl hexanoate (10% in hexane), 8.19 g of neodymium(lll) 2-ethyl hexanoate (12% in hexane), and 84.2 g of yttrium(l 11 )-2-ethyl hexa- noate (10% in hexane), were dissolved in 90.4 g of xylene.

Comparative Example 3

75.24 g of zirconium propylate (70% in propanol), 97.32 g of cerium(lll)-2-ethyl hexanoate in (49% in 2-ethyl hexanoic acid), an 62.8 g of lanthanum(lll)-2-ethyl hexanoate (10% in hexane) were dissolved in 264.64 g of xylene.

Comparative Example 4 59.1 1 g of zirconium propylate (70% in propanol), 105.1 1 g of cerium(lll)-2-ethyl hexanoate in (49% in 2-ethyl hexanoic acid), an 94.38 g of lanthanum(lll)-2-ethyl hexanoate (10% in hexane) were dissolved in 191.41 g of xylene.

Comparative Example 5

43.7 g of zirconium acetylacetonate, 28.5 g of Ce(NC>3)3 · 6 H2O, 3.82 g of lanthanum acety- lacetonate were dissolved in a mixture of 38.5 g of distilled water and 585.6 g of acetic acid.

Comparative Example 6

44.46 g of zirconium acetylacetonate, 24.71 g of Ce(N0₃)3 · 6 H₂0, 1 .31 g of lanthanum(lll) acetylacetonate hydrate, 3.21 g of neodymium(lll) acetylacetonate hydrate, and 6.7 g of yttri- um(lll) acetylacetonate hydrate were dissolved in 719.61 g of acetic acid.

Table 1 : Properties of the emulsions obtained according to Examples 1 to 7.

Ref. Ex. 1 Ref. Ex. 2 Ref. Ex. 3 Ref. Ex. 4 Ref. Ex. 5 Ref. Ex. 6 Ref. Ex. 7

Zr0₂ [wt.-%]<¹> 47.6 47.6 55.0 55.0 55.0 55.0 55.0 Ce0₂ [wt.-%]<¹> 46.2 46.2 40.0 40.0 40.0 40.0 40.0

La₂0₃ [wt.-%]<¹⁾ 6.2 6.2 5 5 5 5 5 xylene [g] 873.7 873.7 815.5 815.5 815.5 815.5 815.5

H₂0 445.4 445.4 410.5 410.5 410.5 410.5 410.5 disperse phase [wt.-%] 40 40 40 40 40 40 40 droplet size distibu- tion<²>:

D50 [μι ] 2 2.6 8.5 1.3 4.3 1.7 0.7

D90 [μιτι] 4 4.2 15.8 2.1 7.3 21.2 3.2

(1 ) wt.-% of the element calculated as the oxide based on the total amount of the rare earth elements, zirconium, and yttrium calculated as the respective oxides.

(2) based on the Fraunhofer - light dispersion measured using a Mastersizer2000 from Malvern Instruments equipped with a Hydro2000SM dispersion module; for the measurements, 0.2 ml_ of the emulsion were dispersed in 120 ml. xylene at 2500 rpm.

Table 2: Properties of the polar and non-polar solutions obtained according to Comparative Examples 1 o 6.

(1 ) wt.-% of the element calculated as the oxide based on the total amount of the rare earth el- ements, zirconium, and yttrium calculated as the respective oxides.

Flame Spray Pyrolysis The precursor emulsions and solutions obtained according to Reference Example 1 to 7 and Comparative Examples 1 to 6 were subject to flame spray pyrolysis using a burner configuration as displayed in Figure 1 under the conditions outlined in Tables 3 and 4. The spray is generated in a two-component nozzle using the precursor emulsion or solution and a gas for dispersion thereof, wherein air or a mixture of nitrogen and oxygen is used as the dispersing gas. The generated spray is ignited by a pilot flame generated from a mixture of methane or ethylene with air and/or a nitrogen/oxygen-mixture. The resulting particles are cooled using a quenching gas and then separated from the gas stream using a woven fabric filter. In the synthesis of the examples and comparative examples, the flow of the precursor solution and the flow of air (or a mixture of nitrogen and oxygen) and ethylene or methane to the main (two-component) and auxiliary nozzles (pilot flame) were regulated such that an average temperature as indicated in Tables 3 and 4 was sustained in the burning chamber for the pyrolysis of the precursor emulsions and solutions, respectively. After having obtained the mixed oxide products from flame spray pyrolysis, the powders were analyzed in their fresh state as well as after having been subject to hydrothermal aging by exposure to air with 10 vol.-% of H2O at a temperature of 1 100 °C for 40 h. The characteristics of the fresh and aged products are shown in Tables 3 and 4 below.

Table 3: Flame spray pyrolysis conditions and product characteristics using precursor emulsions from Reference Examples 1 to 7.

(1 ) average crystallite size calculated with the Scherrer-formula using one of the first four reflections of the cubic phase: CS = (shape factor * X-ray wave length Cu K alpha) / (line broadening at half the maximum intensity (FWHM) in radians * cos Q_hki); a shape factor of 0.94 was assumed for the cubic system.

(2) calculated according tot he formula: secondary particle size (dsp) = 6 / (SBET * rho); SBET, 77K, N2 = BET surface area measured by Is -adsorption at 77K; rho = physical density of a La- Ce/ZrC>2 mixed oxide, obtained by He-displacement to 6.6 g/cm³.

(3) as measured by static light scattering using a Mastersizer2000 from Malvern instruments after dispersion of 0.5 g of the particles in 100 ml propanol and ultrasonic treatment thereof with a sonotrode (level 7; n = 2000 rpm) for 10 min and dispersing 1.5 ml of the resulting suspension on a further 100ml of propanol; for the measurements, an Mie correction was employing, assuming a refractive index (Rl) = 2.2 for a Ce02/ZrC>2 mixed oxide. Table 4: Flame spray pyrolysis conditions and product characteristics using precursor solutions from Comparative Examples 1 to 6.

(1 ) average crystallite size calculated with the Scherrer-formula using one of the first four reflections of the cubic phase: CS = (shape factor * X-ray wave length Cu K alpha) / (line broadening at half the maximum intensity (FWHM) in radians * cos Qhki); a shape factor of 0.94 was assumed for the cubic system.

Determination of the oxygen storage capacity For determining the oxygen storage capacity of the products obtained from Examples 1 to 7 as well as from Comparative Examples 7 to 13, respective samples were impregnated with a solution of palladium nitrate for obtaining a loading of 0.5 wt.-% of Pd, after which the samples were milled, dried, and subsequently calcined at 550 °C. A portion of each sample was then subject to an aging procedure consisting in the treatment of the samples at 1 ,050 °C with air containing 10% steam for 12 h. For further comparison, a commercial sample (40 wt.-% CeC>2, 45 wt.-% Zr0₂, 2 wt.-% La₂0₃, 5 wt.-% Nd₂0₃, and 8 wt.-% Y₂0₃; particle size distribution: D10 = 1.94 μιη, D50 = 13.75 μιη, and D90 = 56.9 μιη) was subject to the same procedure. 100 mg of the respective samples were then subject to alternating 10 second cycles of nitrogen gas containing 1 % oxygen and nitrogen gas containing 2% of carbon monoxide at 450 °C and at a gas hourly space velocity (GHSV) of 60,000 h ¹. A total of 15 cycles were run for each sample and an equivalent for the dynamic behavior of the material was determined. The samples were then subject to 5 cycles of 30 seconds of nitrogen gas containing 1 % oxygen and 30 sec- onds of nitrogen gas containing 2% of carbon monoxide under the same conditions for determining an equivalent to the static behavior of the respective material. During testing, the amount of C0₂ generated in the second phase of the cycle, i.e. in the oxygen-free phases thereof, is analyzed for determining the oxygen storage capacity of the respective sample. The results obtained from the determination of the oxygen storage capacity of the respective samples are dis- played in Table 5.

Table 5: Oxygen storage capacities obtained for samples from Examples 1 to 7, Comparative Examples 7 to 13, and from the commercial sample.

OSC [mmol C0₂ / L of the catalyst] cycle: 10s / 10s 30s / 30s sample: wt-% La, Nd, wt.-% Ce0₂ fresh aged fresh aged and/or Y

Example 1 5.9 47.5 12 5.2 13.1 6.7

Example 2 5.9 47.6 10.9 4.9 12.6 6.6

Example 3 4.7 43.0 10.2 4.2 11.5 6.2

Example 4 4.5 41.0 10.2 3.3 10.9 4.9

Example 5 4.8 40.6 10.8 5.1 11.1 6.5

Example 6 4.8 41.6 9.2 4.7 10.1 6.0

Example 7 4.8 41.6 10.4 5.0 10.8 6.7

Comp. Example 7 6.6 46.4 11.9 1 13.3 1.3

Comp. Example 8 7.0 46.4 11.9 1.5 13 2.5

Comp. Example 9 1&*> 8.3 3.3 9.1 4.6

Comp. Example 10 13.1 36 10.9 1.1 11.9 2.3

Comp. Example 11 &*) 4&*) 9.6 8.3 10.5 7

Comp. Example 12 6.2 45.4 11.8 4 13.3 5.5

Comp. Example 13 6.3 45.3 11.6 4.2 12.9 5.7

Commercial Sample 15 40 9.4 4.9 10.5 6.1 (*) as calculated from the amount of precursor compound used.

Accordingly, as may be seen from the results obtained from comparative testing of the inventive examples, as compared to the testing performed on the samples from the comparative exam- pies obtained from flame spray pyrolysis of polar and non-polar solutions of the precursor compounds as well as compared to the commercial sample, the mixed oxide particles obtained according to the inventive process and in particular displaying a particle size distribution as defined for the mixed oxide particles of the present invention not only display an unexpectedly high oxygen storage capacity based on the relatively low amount of rare earth oxide additive other than Ce and/or of yttrium compared to the comparative and commercial samples. Even more unexpectedly, the loss of oxygen storage capacity observed after ageing of the samples is considerably inferior for the inventive examples compared to the comparative and commercial samples. Thus, the mixed oxide particles obtained according to the inventive process surprisingly display a highly improved performance based on the amount of rare earth oxide other than Ce and/or of Yttrium contained therein compared to the comparative and commercial samples such that a considerably improved oxygen storage component may be obtained according to the present invention, which is furthermore highly cost efficient compared to other materials in view of the reduced amounts of additive materials in addition to ceria and zirconia employed therein.

Claims

1. A process for the production of mixed oxide particles comprising:

(2) forming an aerosol of the dispersion provided in step (1 ); and

(3) pyrolyzing the aerosol of step (2) to obtain mixed oxide particles.

2. The process of claim 1 , wherein the disperse phase comprises a hydrophilic solvent system.

3. The process of claim 2, wherein the hydrophilic solvent system is comprised in droplets, wherein the droplets are preferably stabilized by one or more emulsifying agents.

4. The process of any of claims 1 to 3, wherein the continuous phase comprises a hydrophobic solvent system, the hydrophobic solvent system preferably comprising one or more hydrophobic solvents, wherein the one or more hydrophobic solvents are preferably selected from the group consisting of aliphatic and aromatic hydrocarbons, heterocyclic compounds, and mixtures of two or more thereof.

5. The process of claim 4, wherein the group of aliphatic hydrocarbons comprises one or more selected from branched and/or unbranched aliphatic (C4-Ci2)hydrocarbons, including mixtures of two or more thereof.

6. The process of claim 4 or 5, wherein the group of aromatic hydrocarbons comprises one or more selected from aromatic (C6-Ci2)hydrocarbons, including mixtures of two or more thereof.

7. The process of any of claims 4 to 6, wherein the group of heterocyclic compounds comprises one or more selected from N- and O-containing heterocycles, including mixtures of two or more thereof.

8. The process of any of claims 1 to 7, wherein the dispersion provided in step (1 ) is formed by a process comprising:

(1.c) dispersing the solution in the hydrophobic solvent system by mixing for forming a dispersion.

9. The process of claim 8, wherein mixing in step (1.c) is achieved by use of a homogenizer.

10. The process of any of claims 3 to 9, wherein the one or more emulsifying agents are selected from the group consisting of ionic and nonionic surfactants, including mixtures thereof.

1 1 . The process of claim 10, wherein the ionic surfactants comprise one or more anionic surfactants.

12. The process of claim 10 or 1 1 , wherein the ionic surfactants comprise one or more cation- ic surfactants.

13. The process of any of claims 10 to 12, wherein the ionic surfactants comprise one or more zwitterionic surfactants.

14. The process of any of claims 10 to 13, wherein the nonionic surfactants are selected from the group consisting of (C8-C22)alcohols, (C6-C2o)alcohol ethoxylates with 1 to 8 ethylene oxide units, (C6-C2o)alkyl polyglycosides, polyoxyethylene glycol alkyl ethers, polyoxypro- pylene glycol alkyl ethers, glucoside alkyl ethers, polyoxyethylene glycol alkylphenol ethers, glycerol alkyl esters, sorbitan alkyl esters, polyoxyethylene glycol sorbitan alkyl esters, cocamide monoethanolamine, cocamide diethanolamine, dodecyldimethylamine oxide, block copolymers of polyethylene glycol and polypropylene glycol, polyethoxylated tallow amine, and mixtures of two or more thereof.

15. The process of any of claims 3 to 14, wherein the one or more emulsifying agent is contained in the dispersion in an amount of from 0.01 to 20 wt.-% based on the total weight of the dispersion provided in step (1 ).

16. The process of any of claims 1 to 15, wherein the average particle size D50 of the disperse phase is comprised in the range of from 0.05 to 20 μιτι.

17. The process of any of claims 1 to 16, wherein the particle size D90 of the disperse phase is comprised in the range of from 0.1 to 50 μιτι.

The process of any of claims 1 to 17, wherein the one or more rare earth oxides other than ceria is selected from the group consisting of lanthana, praseodymia, neodymia, and mixtures of two or three thereof.

The process of any of claims 1 to 18, wherein the concentration of the one or more precursor compounds of the one or more rare earth oxides other than ceria and/or of the one or more precursor compounds of yttria calculated as their respective oxides contained in the dispersion provided in step (1 ) is comprised in the range of from to 0.01 to 5 wt.-% based on the total weight of the dispersion provided in step (1 ).

The process of any of claims 1 to 19, wherein the concentration of the one or more precursor compounds of ceria calculated as CeC>2 contained in the dispersion provided in step (1 ) is comprised in the range of from 0.05 to 15 wt.-% based on the total weight of the dispersion provided in step (1 ).

The process of any of claims 1 to 20, wherein the concentration of the one or more precursor compounds of zirconia calculated as ZrC>2 contained in the dispersion provided in step (1 ) is comprised in the range of from 0.05 to 15 wt.-% based on the total weight of the dispersion provided in step (1 )

The process of any of claims 1 to 21 , wherein the concentration of the disperse phase in the dispersion provided in step (1 ) is comprised in the range of from 1 to 80 wt.-% based on the total weight of the dispersion.

The process of any of claims 1 to 22, wherein the one or more precursor compounds of ceria and/or of the rare earth oxides other than ceria and/or of yttria comprise one or more salts.

The process of any of claims 1 to 23, wherein the dispersion provided in step (1 ) further comprises one or more platinum group metals.

The process of claim 24, wherein the dispersion provided in step (1 ) comprises the one or more platinum group metals in an amount ranging from 0.001 to 5 wt.-% calculated as the metal based on the total weight of the dispersion provided in step (1 ).

The process of any of claims 1 to 25, wherein pyrolysis in step (3) is performed in an atmosphere containing oxygen.

The process of any of claims 1 to 26, wherein pyrolysis in step (3) is performed at a temperature comprised in the range of from 800 to 4,000°C.

Mixed oxide particles obtainable and/or obtained by a process according to any of claims 1 to 27.

Mixed oxide particles obtainable from flame spray pyrolysis, wherein the particles comprise ceria, zirconia, and one or more oxides of one or more rare earth elements other than Ce, and/or yttria, and wherein the average particle size distribution is such that

the average diameter D50 is comprised in the range of from 0.3 to 1.4 μιη, and the diameter D10 is comprised in the range of from 0.01 to 0.28 μιτι, and

the diameter D90 is comprised in the range of from 1.5 to 6 μιτι.

The mixed oxide particles of claim 29, wherein the average size of the primary particles of the mixed oxide particles is comprised in the range of from 1 to 150 nm.

The mixed oxide particles of claim 29 or 30, wherein the content of the rare earth oxides other than ceria, and/or of yttria in the mixed oxide calculated as their respective oxides is comprised in the range of from 0.05 to 30 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles.

The mixed oxide particles of any of claims 29 to 31 , wherein the one or more rare earth oxides other than ceria are selected from the group consisting of lanthana, praseodymia, neodymia, and mixtures of two or three thereof.

The mixed oxide particles of any of claims 29 to 32, wherein the content of ceria in the mixed oxide particles is comprised in the range of from 0.5 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles.

The mixed oxide particles of any of claims 29 to 33, wherein the content of ZrC>2 in the mixed oxide particles is comprised in the range of from 1 to 95 wt.-% based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles.

35. The mixed oxide particles of any of claims 29 to 34, wherein the mixed oxide particles comprise one or more transition metals.

36. The mixed oxide particles of claim 35, wherein the mixed oxide particles comprise the one or more transition metals in an amount ranging from 0.01 to 30 wt.-% calculated as the metal and based on the total weight of the one or more rare earth oxides, zirconia, and optional yttria contained in the mixed oxide particles.

37. The mixed oxide particles of any of claims 29 to 36, wherein the BET surface area of the mixed oxide particles is comprised in the range of from 0.5 to 150 m²/g.

38. Use of mixed oxide particles according to any of claims 28 to 37 as an oxygen storage component, a catalyst and/or as a catalyst support.