WO2007000014A1

WO2007000014A1 - Method of making metal oxides

Info

Publication number: WO2007000014A1
Application number: PCT/AU2006/000884
Authority: WO
Inventors: Jose Antonio Alarco; Geoffrey Alan Edwards; Peter Cade Talbot
Original assignee: Very Small Particle Company Pty Ltd
Priority date: 2005-06-29
Filing date: 2006-06-23
Publication date: 2007-01-04
Also published as: TW200704584A

Abstract

A method for producing particles having at least regions of at least one metal oxide having nano-sized grains comprises providing particles of material having an initial, non-equiaxed particle shape, making a mixture of the particles of material and one or more precursors of the metal oxide, and treating the mixture such that the one or more precursors of the metal oxide react with the particles of material to thereby form at least regions of metal oxide on or within the particles, wherein atoms from the particles of material form part of a matrix of the at least one metal oxide and the at least one metal oxide has nano-sized grains and wherein at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.

Description

METHOD OF MAKING METAL OXIDES

Field of the Invention

The present invention relates to metal oxides and to a method of producing metal oxides. The metal oxides suitably have grain sizes in the nanometre scale.

Background of the Invention

Metal oxides are used in a wide range of applications. For example, metal oxides can be used in: • solid oxide fuel cells (in the cathode, anode, electrolyte and interconnect);

• catalytic materials (automobile exhausts, emission control, chemical synthesis, oil refinery, waste management);

• magnetic materials; • superconducting ceramics;

• optoelectric materials;

• sensors (eg. gas sensors, fuel control for engines); -

• structural ceramics (eg. artificial joints).

Conventional metal oxides typically have grain sizes that fall within the micrometre range and often are supplied in the form of particles having particle sizes greater than the micrometre range. It is believed that metal oxides that are comprised of nanometre sized grains will have important advantages over conventional metal oxides. These advantages include lower sintering temperatures, potentially very high surface areas, and sometimes improved or unusual physical properties. However, the ability to economically produce useful metal oxide materials with nanometre-sized grains has proven to be a major challenge to materials science. It has proven to be difficult to make such fine-scale metal oxides, particularly multi-component (complex) metal oxides, with: a) the correct chemical composition; b) a uniform distribution of different atomic species; c) the correct crystal structure; and d) a low cost. Many important metal oxides have not yet been produced with very fine grains, especially multi-component metal oxides. This is because as the number of different elements in an oxide increases, it becomes more difficult to uniformly disperse the different elements at the ultra-fine scales required for nanometre-sized grains. A literature search conducted by the present inventors has shown that very small grain sizes (less than 20nm) have only been attained for a limited number of metal oxides. The reported processes used to achieve fine grain size are very expensive, have low yields and can be difficult to scale up. Many of the fine-grained materials that have been produced do not display particularly high surface areas, indicating dense packing of grains.

At this stage, it will be realised that particles of material are typically agglomerates of a number of grains. Each grain may be thought of as a region of distinct crystallinity joined to other grains. The grains may have grain boundaries that are adjacent to other grain boundaries. Alternatively, some of the grains may be surrounded by and agglomerated with other grains by regions having a different composition (for example, a metal, alloy or amorphous material) to the grains. Methods described in the prior art for synthesising nano materials includes gas phase synthesis, ball milling, co-precipitation, sol gel, and micro emulsion methods. The methods are typically applicable to different groups of materials, such as metals, alloys, intermetallics, oxides and non-oxides.

In our international patent application no. PCT/AU01/01510 (WO 02/42201), we describe a method for producing metal oxide particles having nano-sized grains. This method comprises the steps of: a) preparing a solution containing one or more metal cations; b) mixing the solution from step (a) with one or more surfactants under conditions such that surfactant micelles are formed within the solution to thereby form a micellar liquid; and c) heating the micellar liquid from step (b) to form metal oxide, the heating step being undertaken at a temperature and for a period of time to remove the surfactant and thereby form metal oxide particles.

The metal oxide particles formed by this process have a disordered pore structure. The entire contents of our international patent application no. PCT/AUOl/01510 (WO 02/42201) are expressly incorporated herein by cross reference.

The process described in our international patent application no. PCT/AU01/01510 provides a method that allows for economic production of metal oxide particles. The method is particularly useful for preparing complex metal oxide particles which contain two or more metals. Throughout this specification, the term "complex metal oxide" will be used to describe a metal oxide having two or more metals therein. The complex metal oxide particles prepared by this method have a very homogenous distribution of the metal species throughout the particles. A uniform crystal structure is also obtained, which provides further indication of the homogeneity of the mixed metal oxide product. Furthermore, the process is easily able to be scaled up.

In the process described in our earlier international patent application no. PCT/AU01/01510, step (a) involved preparing a solution containing cations of all of the metals to be incorporated into the complex metal oxide. It was believed that putting all of the metals into solution in assisted in obtaining a homogenous distribution of the metals in the mixed metal oxides produced by the process.

United States patent number 6,139,816 (Liu et al), the entire contents of which are herein incorporated by cross reference, describes a process for the production of metal oxide powders, wherein metal oxide precipitates or metal oxide gels are formed by mixing surfactant with aqueous solutions containing metal salts. The surfactant and salt types are chosen so that a precipitate or gel of the metal oxide forms on mixing. The metal oxide precipitates or metal oxide gels are separated from the rest of the mixture and then further heat treated to obtain metal oxide powders.

United States patent number 5,698,483 (Ong et al), the entire contents of which are herein incorporated by cross reference, describes a process for producing nano-size powders. Ong et al mixes a solution containing metal cations with hydrophilic polymers to form a hydrophilic polymer gel. The hydrophilic polymer gel is then heated to drive off water and organics, leaving a nanometre-sized metal oxide powder.

United States patent number 6,328,947 (Monden et al), the entire contents of which are herein incorporated by cross reference, describes a process for producing fine particles of metal oxide having diameters of about 20nm or smaller by hydrolyzing metal halides in the presence of an organic solvent. In Monden et al, metal oxides are formed by hydrolysis of metal halides in organic solution. The metal oxide precipitates are then separated from the mother solution (for example, by filtration, centrifugation and so forth), washed and then dried. United States patent number 5,879,715 (Higgins et al) and United Staes patent number 5, 11 Q, 111 (Linehan et al), the entire contents of which are herein incorporated by cross reference, describe processes for production of nano-particles by using microemulsion methods. In these processes, a microemulsion is formed and metal oxides are precipitated within the microemulsion micelles, thereby limiting the size of the metal oxide particles to approximately the size of the droplets. In Higgins et al, two water-in-oil emulsions are prepared, one with dissolved metal salt in the water droplets and the other with a reactant in the water droplets. The microemulsions are mixed .and when the reactant-containing droplets contact the metal solution-containing droplets, precipitation of metal oxide occurs. m Linehan et al, a water-in-oil microemulsion is formed with dissolved metal salt in the water droplets. A reactant is then added to the system, for example, by bubbling a gaseous reactant therethrough, to precipitate metal oxide in the water droplets.

Unites States patent number 5,788,950 (hnamura et al), the entire contents of which are herein incorporated by cross reference, describes a process to synthesise complex metal oxide powders using liquid absorbent resin gels, hi hnamura et al, a solution containing at least two dissolved metals is contacted with a liquid absorbent resin such that at least two metals are present, in the liquid absorbent resin after combining with the solution. The liquid absorbent resin is allowed to swell and gel. The swollen gel is treated by changing at least one of the pH or temperature of the swollen gel to form a precursor material. The precursor material is pyrolyzed and calcined to form the mixed metal oxide powder.

DE 19852547, the entire contents of which are herein incorporated by cross reference, describes a process for producing metal oxide powders by treating aqueous solutions of metal salts with an aqueous base to produce a precipitate (condensate) in the presence of a water soluble stabiliser.

United States patent application number 2005/0008777 (McCleskey et al), the entire contents of which are herein incorporated by cross reference, describes a process for forming metal oxide films. The process involves preparing solutions of one or more metal precursors and soluble polymers having binding properties for the one or more metal precursors. After a coating operation, the resultant coating is heated at high temperatures to yield metal oxide films.

AU of the above described United States patents and patent application and DE 19852547 rely upon the formation of solutions containing all of the metal species that become incorporated onto the metal oxide material.

Catalysts are widely used in a large number of industries. Some examples of industries that utilise catalysts include oil refining (especially cracking and reforming), automotive manufacture (especially exhaust catalysts, such as three way catalysts), plastics manufacturing, production of synthesis gas, chemical synthesis processors, absorption and fuel cell manufacture.

A wide range of catalysts are of the type known as supported catalysts. In these catalysts, a catalytic material is supported on a support substrate. The support substrate may be in the form of powder, particles or monoliths. The support substrate is normally selected on the basis of the substrate being able to resist the conditions under which the catalyst is used. It will be appreciated that the conditions under which the catalyst is used may include one or more of elevated temperature, elevated pressure, and aggressive chemical environments. The support substrate may be relatively inert or it may itself have some catalytic activity. Support catalysts also include a catalytic material supported on the support substrate.

Some examples of catalysts and methods for producing catalysts are described in US Patent 6,706,902 to Sturmann et al (assigned to Bayer AG), US Patent No. 6,746,597 in the name of Zhou et al (assigned to Hydrocarbon Technologies, Inc.), US 6,841,512 in the name of Fetcenko et al (assigned to Ovonic Battery Company, Inc.), US Patent Application Publication No. 2005/0009696 in the name of Mao et al (assigned to 3M Innovative Properties Company), US Patent 6,857,431 in the name of Deevi et al (assigned to Philip Morris USA Inc.), and International Patent Application No. WO 2005/002714, filed in the name of William Marsh Rice University. The entire contents of these references are herein incorporated by cross reference.

Production of supported catalysts typically involves mixing the support particles with a catalyst precursor mixture and forming the catalytic material on the surface of the support particles. Where the catalytic material is a metal oxide, the support particle typically does not become involved with the reactions that form the metal oxide. Indeed, except for an interlayer between the metal oxide and the support particle, atoms of the support particle do not become incorporated in the metal oxide matrix. In our earlier United States provisional patent application no 60/582905 and our co-pending International patent application filed on 24 June 2005, we describe a method for making metal oxides by mixing particulate material with a metal cation solution and thereafter forming metal oxide phases. The particles produced by this method are approximately equiaxed particles.

Brief Description of the Invention

In a first aspect, the present invention provides a method for producing particles having at least regions of at least one metal oxide having nano-sized grains, the method comprising the steps of: a) providing particles of material, said particles having an initial, non- equiaxed particle shape; b) making a mixture of the particles of material and one or more precursors of the at least one metal oxide; and c) treating the mixture such that the one or more precursors of the at least one metal oxide react with the particles of material to thereby form at least regions of metal oxide on or within the particles, wherein atoms from the particles of material form part of a matrix of the at least one metal oxide and the at least one metal oxide has nano-sized grains and wherein at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.

In the present invention, it is surprising that the particles of material provided in step (a) become involved in the reaction to produce the metal oxide(s) and thus provide atoms to the metal oxide matrix, with the metal oxide matrix having nano-sized grains, whilst still maintaining a non-equiaxed grain shape in the regions of metal oxide. The particles of material provided in step (a) may have an initial morphology and the morphology of the grains of metal oxide formed in step (c) may have essentially the same morphology as the initial morphology. The initial morphology may include one or more of particle size and particle shape, hi this embodiment, it is surprising that the particles of material become involved in the reaction to produce the metal oxide(s) and thus provide atoms to the metal oxide matrix, with the metal oxide matrix having nano-sized grains, whilst still maintaining the morphology of the original particles.

The at least one metal oxide may be formed as discrete regions on the surfaces of the particles of material. Alternatively, the at least one metal oxide may form a surface layer on the particles of material. As a further alternative, the at least one metal oxide may extend throughout the particles, hi this alternative, the particles may react with the one or more precursors of the at least one metal oxide such that the particles are essentially converted into the at least one metal oxide to thereby obtain the product metal oxide(s).

In one embodiment, the at least one metal oxide is a complex metal oxide. In this embodiment, the atoms from the particles are suitably incorporated into the complex metal oxide matrix such that the complex metal oxide matrix exhibits uniform composition on the nanometre scale. More preferably, the complex metal oxide forms as a single, phase- pure metal oxide.

In another embodiment, two or more phases of metal oxide material are formed.

The complex oxide produced by the present invention may be a single phase material or it may contain multiple phases. Where the complex oxide contains multiple phases, each phase is suitably of different composition to the other phases. One or more of the multiple phases may comprise an oxide of a single metal. Alternatively, one or more of the phases may comprise a complex metal oxide phase. The multiple phases may also comprise one or more phases of an oxide of a single metal and one or more phases of a complex oxide.

The method of the present invention may be operated such that the particulate material does not fully react with the precursor mixture such that the final product comprises a phase from the original particles and a metal oxide phase that has metal atoms from the precursor mixture and the particulate material therein. This "incomplete reaction" of the particulate material may be achieved by two different routes: i) have excess particulate material in the mixture of step (a), such that uncombined particulate material remains after the precursor mix has been consumed; or ii) control the extent of oxide formation, for example, by stopping the oxide formation mechanism, such that "incomplete reaction takes place. This mechanism is not as desirable in instances where the product is to be subsequently used under conditions where the oxide mechanism could be re-commenced. An example of this could be where the product is to be used in a high temperature application.

Suitably, where particulate material remains that has not combined with the metal cations, the remaining particulate material comprises an oxide phase or is converted to ati oxide phase containing metal atoms derived solely from the particulate material.

The present inventors believe that it is more difficult to obtain a completely homogenous mixture in step (a) of the present invention then for processes that utilise all liquid phases. As a result, it is more likely that the final product will include regions or phases of the original particulate material therein.

In the method of the present invention, the product particles may include phases arising from a combination of the initial particles and the precursors. These product particles will generally have a non-equiaxed particle shape. Other metal oxide phases may form solely from metal atoms provided by the precursors and such metal oxide particles may not necessarily be non-equiaxed in shape. Thus, it will be understood that the particles obtained from the method of the present invention may include non-equiaxed particles and equiaxed particles.

The method of the first aspect of the present invention may be used with any method capable of producing complex metal oxides having nano-sized grains and which method previously relied upon all of the precursor or feed metal species being in solution. Such processes include co-precipitation, sol-gel synthesis, micro emulsion methods, surfactant-based processes, processes that use polymers mixed with solutions (such as described in Ong, US patent no. 5,698,483) and polymer-complex methods that use specific polymers to form complexes with the solutions. The process of the first aspect of the present invention may also use any of the processes described in the patents or patent applications described in the "background of the invention" section of this specification and herein incorporated by cross reference.

A very large number of metals may be used in the present invention. Examples include metals from Groups IA, 2A, 3A, 4A, 5A and 6A of the Periodic Table, transition metals, lanthanides and actinides, and mixtures thereof. This list should not be considered to be exhaustive. The mixture may contain one or more different metals. Some examples of metals that are suitable for use in the present invention include cerium, zirconium, aluminium, titanium, yttrium, magnesium, chromium, manganese, cobalt, nickel, copper, zinc, aluminium, strontium, niobium, molybdenum, platinum group metals (including Pt, Pd, Rh, Re), gold, silver and metals from the lanthanide series. It will be appreciated that the present invention should not be considered to be limited solely to this list of metals.

The one or more precursors of the at least one metal oxide are preferably provided in the form of a solution containing one or more metal cations. Step (b) of the process of the present invention, in this embodiment, includes the preparation of a solution containing one or more metal cations. The metal cations are chosen according to the required composition of the metal oxide and according to the atomic species present in the particles also added to the mixture. The solution of one or more metal cations is preferably a concentrated solution. The inventors presently believe that a high concentration of dissolved metal is preferred for achieving the highest yield of product.

The metal cation solution is suitably produced by mixing a salt or salts containing the desired metal(s) with a solvent. Any salt soluble in the particular solvent may be used. The metal cation solution may also be produced by mixing a metal oxide or metal oxides or a metal or metals with appropriate solvent(s).

A number of solvents can be used to prepare the metal cation solution. The solvents are preferably aqueous-based solvents. Examples of suitable solvents include water, nitric acid, hydrochloric acid, sulphuric acid, hydrofluoric acid, other organic acids, ammonia, alcohols, acetic acid, formic acid, other organic acids and mixtures thereof. This list should not be considered exhaustive and the present invention should be considered to encompass the use of all suitable solvents.

The particles of material used in the present invention suitably have a particle size that has at least one dimension that is similar to the grain size of the metal oxide produced by the method. It is preferred that the particles of material present in the mixture have a particle size that has at least one dimension that falls within the range of about lnm to about 250nm, more preferably 1-lOOnm, even more preferably l-50nm, further preferably l-25nm, further preferably 1-lOnm, most preferably l-4nm. In some embodiments of the present invention, the particles may be of large aspect ratio (i.e. the ratio of length to width of a particle) and the length of such particles may be somewhat greater than the dimensions given above.

The particles of material suitably provide one or more further metals for incorporation into the metal oxide. The particles of material may be present in the form of particles of a metal, particles of two or more metals, particles of metal alloy containing two or more metals, or mixtures thereof, hi practice, fine particles of metal are often quite reactive and this may introduce difficulties in handling the metal particles, as well as raising safety issues. Preferably, the particles of material comprise particles of metal compounds, or a mixture of particles of different metal compounds, or particles containing mixed metal compounds, or mixtures thereof. The particles may be in the form of oxides, nitrates, chlorides, sulfates, hydroxides, more complex oxy-hydrides such as those that may be produced using sol-gel type methods, etc. This list is not exhaustive. It is preferred that the particulate material contains one or more metal oxides, hydroxides or oxy-hydrides.

It is preferred that the particles of material are evenly dispersed throughout the mixture that is treated in step (b) of the process of the first aspect of the present invention. In this regard, the mixture may be suitably treated to disperse the particles of material throughout the solution. Many techniques for dispersion of particles in liquids are known. Dispersion may be achieved by control of solution characteristics (e.g. pH, temperature, addition of specific dispersants) together with appropriate mixing techniques. Mixing may be achieved by using any suitable known mixing apparatus, including high speed impellers, flow mixers, roll mills and ultrasonic mixers. The particles of material may be dispersed after the solution has been formed. Alternatively, the particles of material may be mixed with the soluble metal compound(s) prior to addition of the solute to form the solution. As a further alternative, the particles may be dispersed in a liquid and the precursors subsequently added to that dispersion.

The method may involve dispersing the support particles in a solution having pH that promotes dispersion and minimises aggregation of the support particles, followed by mixing that dispersion with a solution or mixture containing the one or more precursors of the catalytic material. The pH of the solution in which the support particles are dispersed is dependent upon the type of particles being dispersed in the solution. It will be understood that the support particles should not be detrimentally affected by the preparation conditions used. For example, the particles should not undesirably dissolve under the pH conditions used (or, to put it another way, the pH conditions should be selected such that dissolution of the support particles is minimal). It has been found by the present inventors that the step of dispersing the support particles in the solution prior to mixing with the one or more precursors of the catalytic material tends to result in a better distribution of catalytic material on the support particles with less aggregation of the support particles.

The dispersion step may result in the particles becoming monodispersed (i.e. agglomerates of the particles largely break up into individual particles). However, in some instances, it may be desirable to avoid monodispersion of the particles. An example where monodispersion could be avoided involves the use of branched particles that comprise a branched aggregate of particles. The branched particles may provide desirable porosity and surface area properties and thus it may be useful to disperse those particles without causing the aggregates of smaller particles to break down.

Other materials may be added to the mixture formed in step (b), depending upon the particular process chosen to form the metal oxide. The other materials added to the mixture may include surfactants, emulsifying agents, swellable polymers, hydrophilic polymers, immiscible liquids (where microemulsion techniques are used), precipitation agents, hydrolysing agents and the like.

The mixture of step (b) may be treated in a number of different ways to form the metal oxide. Some treatments include: i. heat treatment, typically by heating to an elevated temperature; ii. precipitation, preferably followed by heat treatment; iii. hydrolysis, preferably followed by heat treatment; iv. gelling, preferably followed by heat treatment; v. calcination; vi. pyrolysis.

Again, the choice of treatment used will depend upon the particular process chosen.

In some embodiments, step (c) of the present invention involves treating the mixture such that the dissolved metal cations initially form a solid precursor phase intermixed with the particulate material. The solid precursor phase and the particulate material then combine to form the complex metal oxide phase or phases, hi such embodiments, step (c) may include a heat treatment step that facilitates the combining of the solid precursor phase with the particulate material to form the complex oxide phase(s). In some embodiments, the heat treatment also assists in forming the solid precursor phase from the mixture of step (a). In instances where step (c) includes a heating step, the heating step encompasses any heat treatment that results in the formation of the metal oxide(s). The heating step may involve heating to an elevated temperature, for example, from 200°C to 1300°C, preferably from 300⁰C to 1200°C. The actual temperatures and duration of heating is somewhat dependent upon the particular oxides being produced. The skilled person would readily be able to ascertain the required temperature and heating times required to form any particular metal oxide. The method of the present invention is particularly suitable for use with the process described in our International patent application no. PCT/AUOl/01510.

Accordingly, in a second aspect the present invention provides a method for producing complex metal oxide particles having nano-sized grains, the method comprising: a) preparing a solution containing one or more metal cations; b) mixing the solution from step (a) with surfactant under conditions such that surfactant micelles are formed within the solution to thereby form a micellar liquid; and c) heating the micellar liquid from step (b) to form metal oxide, the heating step being undertaken at a temperature and for a period of time to remove the surfactant and thereby form metal oxide particles; characterised in that the micellar liquid heated in step (c) also contains particles of material of non-equiaxed particle shape, said particles containing one or more further metals in the form of metal(s) or metal compound(s) and the the one or more metal cations react with the particles of material to thereby form at least regions of metal oxide on or within the particles of material, wherein atoms from the particles of material form part of a matrix of the at least one metal oxide and the at least one metal oxide has nano-sized grains and wherein at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.

The particles of material provided in step (b) may have an initial morphology and the morphology of the grains of the at least one metal oxide formed in step (c) may have essentially the same morphology as the initial morphology. The initial morphology may include one or more of particle size and particle shape. In this embodiment, it is surprising that the particles of material become involved in the reaction to produce the metal oxide(s) and thus provide atoms to the metal oxide matrix, with the metal oxide matrix having nano- sized grains, whilst still maintaining the morphology of the original particles. The method of the second aspect of the present invention may optionally further comprise the steps of treating the mixture from step (b) to form a gel and heating the gel to form the particles of metal oxide. Step (b) of the method of the second aspect of the present invention involves adding surfactant to the mixture to create a surfactant/liquid mixture. Preferably, the surfactant is added to the solution under conditions in which micelles are formed, such that a micellar liquid is formed. A micellar liquid is formed when surfactant is added in sufficient quantity such that the surfactant molecules aggregate to form micelles. In a micellar liquid, micelles do not exhibit a significant degree of order, therefore the viscosity of the liquid is usually much less than that of more ordered liquid crystal phases, which are commonly gel-like. Use of micellar liquids as opposed to liquid crystals therefore enables simple, rapid and thorough mixing of the solution and surfactant, which is important for commercial production processes, hi some embodiments, the amount of surfactant mixed with the solution is sufficient to produce a micellar liquid in which the micelles are closely spaced. The conditions under which the micellar liquid is formed will depend upon the particular surfactant(s) being used. In practice, the main variables that need to be controlled are the amount of surfactant added and the temperature. For some surfactants, the temperature should be elevated, whilst for others room temperature or below is necessary.

Any surfactant capable of forming micelles may be used in the present invention. A large number of surfactants may be used in the invention, including non-ionic surfactants, cationic surfactants, anionic surfactants and zwitteronic surfactants. Some examples include Brij C₁₆H₃₃(OCH₂CH₂)₂OH, designated C₁₆EO₂, (Aldrich); Brij 30, C₁₂EO₄, (Aldrich); Brij 56, C₁₆EO₁₀, (Aldrich); Brij 58, C₁₆EO₂₀, (Aldrich); Brij 76, C₁₈EO₁₀, (Aldrich); Brij 78, C₁₆EO₂₀, (Aldrich); Brij 97, C₁₈H₃₅EO₁₀, (Aldrich); Brij 35, C₁₂EO₂₃, (Aldrich); Triton X-IOO,

CH₃C(CH₃)₂CH₂C(CH₃)₂C₆H₄(OCH₂CH₂)χOH,x=10(av), (Aldrich); Triton X-114, CH₃C(CH₃)₂CH₂C(CH₃)₂C₆H₄(OCH)₂CH₂)₅OH (Aldrich); Tween 20, polyethylene oxide) (20) sorbitan monokayrate (Aldrich); Tween 40, poly(ethylene oxide) (20) soribtan monopalmitate (Aldrich); Tween 60, poly(ethylene oxide) (20) sorbitan monostearate (Aldrich); Tween, poly(ethylene oxide) (20) sorbitan monooleate (Aldrich); and Span 40, sorbitan monopalmitate (Aldrich), Terital TMN 6, CH3CH(CH3)CH(CH₃)CH₂CH₂CH(CH₃)(OCH₂CH₂)₆OH (Fulka); Tergital TMN 10, CH₃CH(CH3)CH(CH₃)CH₂CH₂CH(CH₃)(OCH₂CH2)₁oOH (Fulka); block copolymers having a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (EO-PO-EO) sequence centered on a (hydrophobic) poly(propylene glycol) nucleus terminated by two primary hydroxyl groups; Pluronic L121 {_Msv =4400), EO₅PO₇₀EO₅ (BASF); Pluronic L64 (_Mav =2900), EP₁₃PO₃₀EO₁₃ (BASF); Pluronic P65 (_Mav =3400), EP₂₀PO₃₀EO₂₀ (BASF); Pluronic P85 (_Mzv =4600), EO₂₆PO₃₉EO₂₆ (BASF); Pluronic P103 (_Mav =4950), EO₁₇PO₅₆EO₁₇ (BASF); Pluronic P123 (_Mav =5800), E0₂₀P0₇oE0₂₀, (Aldrich); Pluronic F68 (_Mav = 8400), E0₈₀P0₃oE0₈₀ (BASF); Pluronic F127 {_Msv =12600), E0₁₀₆P0₇oE0₁₀₆ (BASF); Pluronic F88 (_Mav =11400), EO₁₀₀PO₃₉EO₁₀₀ (BASF); Pluronic 25R4 (_May =3600), PO₁₉EO₃₃PO_I9 (BASF); star diblock copolymers having four EO_n-PO₁₁₁ chains (or in reverse, the four PO_n-EO_1n chains) attached to an ethlenediamine nucleus, and terminated by secondary hydroxyl groups; Tetronic 908 (_MZV =25000), (EO₁₁₃PO₂₂)₂NCH₂CH₂N(PO₁₁₃EO₂₂)₂ (BASF); Tetronic 901 (_Mav =4700), (EO₃PO_1S)₂NCH₂CH₂N(PO_I8EO₃^ (BASF); and Tetronic 90R4 (_Mav =7240), (PO₁₉EO₁₆)₂ NCH₂CH₂N(EO₁₆PO₁₉)₂ (BASF)

The above surfactants are non-ionic surfactants. Other surfactants that can be used include:

Anionic surfactant:

Sodium dodecyl sulfate CH₃(CH₂)₁ ^SO₃NA

There appears to be several manufacturers. Sigma is an example.

Cationic surfactants: Cetyltrimethylammonium chloride CH₃(CH₂)₁₅N(CH₃)₃C1 Aldrich

Cetyltrimethylammonium bromide CH₃(CH₂)₁₅N(CH₃)₃BT Aldrich

Cetylpyridinium chloride C₂₁H₃₈NC1 Sigma.

This list should not be considered to be exhaustive. The micellar liquid provided to step (c) of the second aspect of the present invention also contains particles of material containing one or more further metals in the form of metals or metal compounds or both. The particles of material used in the second aspect of the present invention suitably have a particle size that is similar to the grain size of the mixed metal oxide produced by the method. It is preferred that the particles of material present in the micellar liquid have a particle size that falls within the range of about lnm to about 250nm, more preferably 1-lOOnm, even more preferably l-50nm, further preferably l-25nm, further preferably 1-lOnm, most preferably l-4nm. It is considered that the larger the particle size, the more difficult it is to obtain chemical homogeneity with the other elements in the compound. In some embodiments of the present invention, the particles may be of large aspect ratio (i.e. the ratio of length to width of a particle) and the length of such particles may be somewhat greater than the dimensions given above. The particles of material may be added at any stage of the process of the second aspect prior to the heating step which forms the mixed metal oxide material. For example, the particulate material may be mixed with the metal compounds that are dissolved in step (a). Alternatively, the particles of material may be added to the solvent that is used in step (a) to form the solution containing one or more metal cations. As a further alternative, the particles of material may be added to the solution formed in step (a). In yet a further alternative, the particles of material may be added to the one or more surfactants mixed with the solution in step (b). In a still further alternative, the particles of material may be added to the micellar liquid produced in step (b). As a further alternative, the particles of material are dispersed in a liquid and the metal cations and surfactant added to that dispersion. It is preferred that the particles of material are evenly dispersed throughout the micellar liquid that is treated in step (c) of the process of the second aspect of the present invention. In this regard, where the particles of material are added prior to formation of the micellar liquid, the solution produced in step (a) is suitably treated to disperse the particles of material throughout the solution. Many techniques for dispersion of particles in liquids are known. Dispersion may be achieved by control of solution characteristics (e.g. pH, temperature, addition of specific dispersants) together with appropriate mixing techniques. Mixing may be achieved by using any suitable known mixing apparatus, including high speed impellers, flow mixers, roll mills and ultrasonic mixers.

Similarly, if the particles of material are added to the micellar liquid formed in step (b) the particles of material is preferably mixed with and dispersed within the micellar liquid. Again, any suitable mixing apparatus may be used.

The particles of material that are contained in the micellar liquid treated in step (c) provides one or more metals for incorporation into the mixed metal oxide particles. The one or more metals may be present in the form of a metal_, or mixture of metals or metal alloys. In this embodiment, the particles of material comprises particles of a metal, particles of two or more metals, particles of metal alloy containing two or more metals, or mixtures thereof. In practice, fine particulates of metal are often quite reactive and this may introduce difficulties in handling the metal particles, as well as raising safety issues.

Preferably, the particles of material containing one or more further metals comprises particles of metal compounds, or a mixture of particles of different metal compounds, or particles containing mixed metal compounds, or mixtures thereof. The particles may be in the form of oxides, nitrates, chlorides, sulfates, hydroxides, more complex oxy-hydrides such as those that may be produced using sol-gel type methods, etc. It is preferred that the particles of material contain one or more metal oxides, hydroxides or oxy-hydrides.

Step (c) of the method of the second aspect of the present invention typically involves heating of the mixture from step (b) to an elevated temperature to thereby form the metal oxide particles. This step may optionally be preceded by a step of treating the surfactant/liquid mixture to form a gel. Commonly, the gel forms due to ordering of the micelles to form a liquid crystal. Typically, it is sufficient to change the temperature of the mixture to form the gel. For some mixtures, cooling will result in gel formation. For other mixtures, heating will result in gel formation. This appears to be dependent upon the surfactant(s) used.

If the optional step of forming a gel is used in the method, the heating of step (c) involves heating the gel.

The heating step results in the formation of the metal oxide and the pore structure of the particles. The heating step encompasses any heat treatment that results in the formation of the metal oxide(s). The heating step may involve heating to an elevated temperature, for example, from 200°C to 1300°C. The actual temperatures and duration of heating is somewhat dependent upon the particular oxides being produced. The skilled person would readily be able to ascertain the required temperature and heating times required to form any particular metal oxide.

The present inventors believe that the process of the present invention may involve localised exothermic reactions occurring, which could lead to highly localised temperatures

The heating step may involve a rapid heating to the maximum desired temperature, or it may involve a much more closely controlled heat treatment regime. For example, the heating step may be carried out under a controlled atmosphere. The heating step may involve heating to a drying temperature (generally below the boiling temperature of the mixture) to dry the mixture, followed by a slow ramp up to the maximum applied temperature, or followed by a series of incremental increases to intermediate temperatures before ultimately reaching the maximum applied temperature. The duration of the heating step may vary widely, with a preferred time in step (c) being from 15 minutes to 24 hours. It will be appreciated that step (c) is intended to encompass all heating profiles that result in the formation of particles of metal oxide.

The heating step (c) of the present invention encompasses all such heating steps that result in the formation of the desired metal oxide particles. The heating step may be carried out using heating apparatus known by the person of skill in the art to be suitable for such purposes. Examples include hot plates or other heated substrates, ovens, stationary table furnaces, rotary table furnaces, induction furnaces, fluid bed furnaces, bath furnaces, flash furnaces, tube furnaces, infrared furnaces, muffle furnaces, drop furnaces, belt furnaces, rotary furnaces, rotary kirns, rotary dryers, spray dryers, spin-flash dryers, drum dryers, reaction vessels, and flash calciners. The present inventors have shown that the results of the method of the present invention are particles of metal oxide having nano-sized grains with significant amounts of crystallinity, disordered pore structures, broad distributions of pore sizes and an essentially homogenous composition throughout.

The metal oxide particles produced by preferred embodiments of the method have nano-sized grains. Preferably, the grain size falls within the range of l-250nm, more preferably 1-lOOnm, even more preferably l-50nm, still even more preferably l-20nm, further even more preferably 2-lOnm, most preferably 2-8nm.

The grain size was determined by examining a sample of the particles using TEM (transmission electron microscopy), visually evaluating the grain size and calculating an average grain size therefrom. The particles may have varying particle size due to the very fine grains aggregating or cohering together. The particle size may vary from the nanometre range up to the micrometre range or even larger. The particles may have large specific surface areas (for the particular metal oxide, when compared with prior art processes for making those particles) and exhibit a broad distribution of pore sizes. In all aspects of the process of the present invention, it may be desirable to add a pore-forming material to the mixture to form a porous complex metal oxide having a desired pore structure. In this embodiment, the pore-forming material is added to the mixture prior to forming the complex metal oxide and removed from the complex metal oxide either during the step of forming the metal oxide or after formation of the metal oxide to leave a porous complex metal-oxide. The pore-forming material may be polymer-based pore formers, polymer-based particles such as latex, salts or other particles such as carbon black. The pore forming material may be selected to provide pore sizes in the range of approximately 7nm to 250nm. The pore forming material is suitably selected to produce a porous complex metal oxide exhibiting enhanced high temperature stability.

The grain size of the porous complex metal oxide may fall within the range of 1- 150nm. The use of a pore forming material to produce complex metal oxides of enhanced high temperature stability is described in our co-pending United States provisional patent application no. US (60/538 867), the entire contents of which are herein incorporated by cross reference.

The method of the present invention may be used to make metal oxide particles. The metal oxide particles may have a grain size substantially in the range from l-250nm. Preferably, the grain size falls within the range of 1-lOOnm, more preferably l-50nm, more preferably l-20nm, even more preferably 2-10nm, most preferably 2-8nm.

The particles are preferably substantially crystalline and contain only small or negligible amounts of amorphous material. The particles are suitably phase pure and have essentially uniform composition. The particles may have a single metal oxide lattice containing two or more metals. The particles may have two or more metal oxide phases. One or more of those oxide phases may be complex oxide phases. Generally, the grains of metal oxide are non-equiaxed.

The method of the present invention surprisingly has been found to be able to form complex metal oxides having enhanced thermal stability when compared with previous methods that utilised solutions of precursors only. By enhanced thermal stability, it is meant that the loss of specific surface area as a result of exposure to high temperature is reduced. The particles having the metal oxide phase(s) are also of generally non-equiaxed particle shape. Brief description of the drawings

Figure 1 shows a cross-sectional diagram of an initial particle used in an embodiment of the present invention;

Figure 2 shows a cross-sectional diagram of a particle having a region of metal oxide made in accordance with an embodiment of the present invention;

Figure 3 shows a cross-sectional diagram of another particle having a region of metal oxide made in accordance with an embodiment of the present invention;

Figure 4 shows a cross-sectional diagram of another particle having a layer of metal oxide surrounding a core of the original material of the particle and made in accordance with an embodiment of the present invention;

Figure 5 shows a cross-sectional diagram of another particle composed entirely of metal oxide and made in accordance with an embodiment of the present invention;

Figure 6 shows an x-ray diffraction trace of the material in example 1;

Figure 7 shows a TEM micrograph of the material made in example 1; and Figure 8 shows an x-ray diffraction traces of the material made in example 2, heat treated to various temperatures.

Detailed description of the drawings

Figure 1 shows a cross-sectional diagram of an initial particle used in an embodiment of the present invention. The particle 10 of figure 1 is generally oval in shape.

In figure 2, a particle similar to that shown in Figure 1 has been used in an embodiment of the method of the present invention to form a region 12 of metal oxide on the particle 10. As can be seen in Figure 2, the region 12 of metal oxide extends into the particle 10. Region 12 of metal oxide has been formed by a reaction involving atoms from the particle 10 and precursors mixed with the particle 10 to form the region 12 of metal oxide. The matrix of metal oxide in region 12 incorporates atoms from the particle 10.

In figure 3, a particle similar to that shown in Figure 1 has been used in an embodiment of the method of the present invention to form a region 14 of metal oxide on the particle 10. As can be seen, the region 14 of metal oxide rests on the particle 10. However, the metal oxide in region 14 includes atoms from the particle 10 throughout the metal oxide matrix. This may occur, for example, by diffusion of atoms from the particle 10 into the region 14 of metal oxide. It will be appreciated that the region 14 of metal oxide may also extend below the original surface level of the particle 10.

In figure 4, a particle similar to that shown in Figure 1 has been used in an embodiment of the method of the present invention to form a layer 16 of metal oxide surrounding a core of material 10' remaining from the original particle 10.

In figure 5, a particle similar to that shown in Figure 1 has been used in an embodiment of the method of the present invention to form a region 18 of metal oxide that occupies essentially all of the original volume of the original particle 10.

Examples

Example 1.

A composition MgAl₂O₄ was prepared as follows. 11.77g of boehmite (aluminium hydroxide) needle-shaped nanoparticles (Dispal X-O, Sasol Corporation) were dispersed into lOOmls of water. 21 g of magnesium nitrate hexahydrate was dissolved in 38mls of water. The solution was added to the dispersion, then 24.4g of Erunon LA2 surfactant was then added followed by stirring. This mixture was heated slowly to 500⁰C.

An XRD trace (Co radiation) is shown in figure 6. The trace showed the material was MgAl₂O₄. A TEM micrograph of this material is shown in figure 7. The

MgAl₂O₄ has essentially retained the needle morphology of the original boehmite needles.

Example 2.

A composition CuAl₂O₄ was prepared in a similar manner to example 1. Erunon LA4 surfactant was used in place of LA2. Figure 8 shows XRDs of this material after heat treatment to 500⁰C, 75O⁰C, 900⁰C and 1000⁰C. The surface area was -145 m²/g and pore volumes from ~2nm to 150nm was 1 cc/g, from 10-~150nm 0.93 cc/g, and from 50-~150nm

0.42 cc/g. Clearly this composition requires a higher temperature heat treatment to form the complex oxide, compared to example 1. The proportion Of CuAl₂O₄ present increases as the temperature is increased. Clearly the heat treatment may be stopped at any stage to attain a desired mix of phases. Comparative Example 1.

CuAl₂O₄ was produced in a similar manner to example 2, except that the aluminium was provided via dissolved aluminium nitrate nonahydrate, and no particulate matter was used. Table 1 compares surface areas obtained after heat treating to 85O⁰C, 900⁰C and 1000⁰C. After these heat treatments, the XRD traces were very similar for this material and the material in example 2, i.e. the degree of formation of CuAl₂O₄ was very similar. Clearly the material of example 2 has considerably higher surface area at the higher temperatures.

Table 1

Example 3.

A composition CuAl₂O₄ was prepared in a similar manner to example 2, except that polyethylene glycol was used instead of Erunon LA4. XRDs after heat treatment to 1000⁰C showed mostly CuAl₂O₄.

Example 4.

A composition 40wt% CuO 35wt% ZnO 25wt% Al₂O₃ was prepared in a similar manner to example 2. After heat treatment to 400⁰C the surface area was 75m²/g. XRD showed a mixture of phases present.

Example 5

MgAl₂O₄ with ~25wt% Ni in the form of nickel oxide was prepared in a similar manner to example 2. 14.54g of Dispal X-O boehmite needles was dispersed in 125g water. 27.05g of magnesium nitrate hexahydrate was dissolved in 5Og water and added to the dispersion. 1Og nickel carbonate was dissolved in 15g HNO₃ solution (70 wt% concentration) and 3Og water, and this was also added to the dispersion. 47g of Erunon LA4 surfactant was mixed in and the mixture heated from room temperature to 45O⁰C. XRD showed the presence of MgAl₂O₄ peaks, similar to the material in example 2, and additional peaks that could be attributed to NiO. The surface area was ~150 mVg and pore volumes from ~2nm to 150nm was 0.91cc/g, from 10 to ~150nm 0.85 cc/g, and from 50 to ~150nm 0.4cc/g. TEM showed nanometre sized needle-shaped MgAl₂O₄ grains, and very fine NiO material.

This sample was further heat treated for 1.5 h at 800⁰C. XRD showed similar peak positions. The surface area of this material was 112 m²/g and pore volumes from ~2nm to 150nm was 0.82cc/g, from 10 to ~150nm 0.78 cc/g, and from 50 to ~150nm 0.41 cc/g. TEM showed nanometre sized needle-shaped MgAl₂O₄ grains, and more equiaxed NiO grains, ranging between approximately 5nm and 30nm diameter.

Example 6

MgAl₂O₄ with ~15wt% Ni in the form of nickel oxide was prepared similarly to example 3. After heat treatment for 1.5h at 800⁰C, the surface area was ~124 m²/g and pore volumes from ~2nm to 150nm was 0.73cc/g, from 10 to ~150nm 0.65 cc/g, and from 50 to ~150nm 0.22 cc/g. TEM showed nanometre sized needle-shaped MgAl₂O₄ grains, and more equiaxed NiO grains, ranging between approximately 5nm and 30nm diameter.

Example 7

A composition 15wt% Ni on MgAl₂O₄ was prepared in a similar manner to example 1, except that DISPAL 23N4-80 plate-shaped boehmite nanoparticles were used instead of DISPAL X-O, and the material was heat treated to 45O⁰C.

An XRD trace (Co radiation) showed the material was MgAl₂O₄ with fine nickel oxide. TEM showed the MgAl₂O₄ retained the plate-like morphology of the original boehmite.

The surface area was 171 m²/g, and the pore volume for pores between 2nm and ~200nm was 0.8 cc/g. Example 8

A composition 15wt% Ni on MgAl₂O₄ was prepared in a similar manner to example 7, except that branch-like boehmite nanoparticles (DISPAL 18HP) were used instead of DISPAL 23N4-80.

An XRD trace (Co radiation) showed the material was MgAl₂O₄ with fine nickel oxide. TEM showed the MgAl₂O₄ retained morphology similar to the original boehmite.

Those skilled in the art will appreciate that the present invention may be susceptible to variations and modifications other than those specifically described. It is to be understood that the present invention encompasses all such variations and modifications that fall within its spirit and scope.

Claims

Claims.

1. A method for producing particles having at least regions of at least one metal oxide having nano-sized grains, the method comprising the steps of: d) providing particles of material, said particles having an initial, non- equiaxed particle shape; e) making a mixture of the particles of material and one or more precursors of the at least one metal oxide; and f) treating the mixture such that the one or more precursors of the at least one metal oxide react with the particles of material to thereby form at least regions of metal oxide on or within the particles, wherein atoms from the particles of material form part of a matrix of the at least one metal oxide and the at least one metal oxide has nano-sized grains and wherein at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.

2. A method as claimed in claim 1 wherein the particles of material provided in step (a) have an initial morphology and the morphology of the grains of metal oxide formed in step (c) have essentially the same morphology as the initial morphology.

3. A method as claimed in claim 2 wherein the initial morphology includes one or both of particle size and particle shape.

4. A method as claimed in claim 1 wherein the at least one metal oxide is formed as discrete regions on the surfaces of the particles of material, or the at least one metal oxide forms a surface layer on the particles of material, or the at least one metal oxide extends throughout the particles.

5. A method as claimed in claim 1 wherein the at least one metal oxide is a complex metal oxide.

6. A method as claimed in claim 5 wherein atoms from the particles are incorporated into the complex metal oxide matrix such that the complex metal oxide matrix exhibits uniform composition on the nanometre scale.

7. A method as claimed in claim 1 wherein two or more phases of metal oxide material are formed.

8. A method as claimed in claim 1 wherein the particulate material does not fully react with the precursor mixture such that the final product comprises a phase from the original particles and a metal oxide phase that has metal atoms from the precursor mixture and the particulate material therein.

9. A method as claimed in claim 8 wherein excess particulate material is present in the mixture of step (a), such that unreacted particulate material remains after the precursor mix has been consumed.

10. A method as claimed in claim 1 wherein product particles include phases arising from a combination of the initial particles and the precursors, said product particles generally having a non-equiaxed particle shape and other product particles containing metal oxide phases formed solely from metal atoms provided by the precursors, said other product particles not being non-equiaxed in shape.

11. A method as claimed in claim 1 wherein the metal oxide is produced by a co-precipitation process, a sol-gel synthesis, a micro emulsion method, a surfactant-based process, a process that uses polymers mixed with solutions or a polymer-complex method that use specific polymers to form complexes with the solutions.

12. A method as claimed in claim 1 wherein the at least one metal oxide includes one or more metals from Groups IA, 2A, 3A, 4A, 5A and 6A of the Periodic Table, transition metals, lanthanides and actinides, and mixtures thereof.

13. A method as claimed in claim 12 wherien the metal is selected from the group consisting of cerium, zirconium, aluminium, titanium, yttrium, magnesium, chromium, manganese, cobalt, nickel, copper, zinc, aluminium, strontium, niobium, molybdenum, platinum group metals (including Pt, Pd, Rh, Re), gold, silver and metals from the lanthanide series and mixtures thereof.

14. A method as claimed in claim 1 wherein the one or more precursors of the at least one metal oxide are provided in the form of a solution containing one or more metal cations.

15. A method as claimed in claim 14 wherein step (b) comprises making a mixture of the particles of material and a solution.

16. A method as claimed in claim 1 wherein the particles of material have a particle size that has at least one dimension that is similar to the grain size of the metal oxide produced by the method.

17. A method as claimed in claim 16 wherein the particles of material present in the mixture have a particle size that has at least one dimension that falls within the range of about lnm to about 250nm.

18. A method as claimed in claim 1 wherein the particles of material are present in the form of particles of a metal, particles of two or more metals, particles of metal alloy containing two or more metals, or mixtures thereof.

19. A method as claimed in claim 1 wherein the particles of material comprise particles of metal compounds, or a mixture of particles of different metal compounds, or particles containing mixed metal compounds, or mixtures thereof.

20. A method as claimed in claim 19 wherein the particles are in the form of oxides, nitrates, chlorides, sulfates, hydroxides, or oxy-hydrides.

21. A method as claimed in claim 1 wherein the particles of material are evenly dispersed throughout the mixture that is treated in step (b).

22. A method as claimed in claim 21 wherein the particles of material are dispersed after the solution has been formed or the particles material are mixed with a soluble metal compound(s) prior to addition of a solute to form the solution or the particles are dispersed in a liquid and the precursors subsequently added to that dispersion.

23. A method as claimed in claim 22 comprising dispersing the support particles in a solution having pH that promotes dispersion and minimises aggregation of the support particles, followed by mixing that dispersion with a solution or mixture containing the one or more precursors of the metal oxide.

24. A method as claimed in claim 23 wherein the dispersion step results in the particles becoming monodispersed.

25. A method as claimed in claim 23 wherein the particles of material comprise a branched aggregate of particles and the particles are dispersed without causing the aggregates to break down.

26. A method as claimed in claim 1 wherein the mixture of step (b) is subjected to one of the following steps to form the metal oxide:

(i) heat treatment, by heating to an elevated temperature; (ii) precipitation, optionally followed by heat treatment;

(iii) hydrolysis, optionally followed by heat treatment;

(iv) gelling, optionally followed by heat treatment;

(v) calcination;

(vi) pyrolysis.

27. A method for producing complex metal oxide particles having nano-sized grains, the method comprising: a) preparing a solution containing one or more metal cations; b) mixing the solution from step (a) with surfactant under conditions such that surfactant micelles are formed within the solution to thereby form a micellar liquid; and c) heating the micellar liquid from step (b) to form metal oxide, the heating step being undertaken at a temperature and for a period of time to remove the surfactant and thereby form metal oxide particles; characterised in that the micellar liquid heated in step (c) also contains particles of material of non-equiaxed particle shape, said particles containing one or more further metals in the form of metal(s) or metal compound(s) and the the one or more metal cations react with the particles of material to thereby form at least regions of metal oxide on or within the particles of material, wherein atoms from the particles of material form part of a matrix of the at least one metal oxide and the at least one metal oxide has nano-sized grains and wherein at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.

28. A method as claimed in claim 27 wherein the particles of material provided in step (b) have an initial morphology and the morphology of the grains of the at least one metal oxide formed in step (c) is essentially the same morphology as the initial morphology.

29. A method as claimed in claim 28 wherein the initial morphology includes one or more of particle size and particle shape.

30. A method as claimed in claim 27 further comprising the steps of treating the mixture from step (b) to form a gel and heating the gel to form the metal oxide.

31. A method as claimed in claim 27 wherein the surfactant is selected from the group consisting of non-ionic surfactants, cationic surfactants, anionic surfactants and zwitteronic surfactants.

32. A method as claimed in claim 27 wherein the particles of material have a particle size that is similar to the grain size of the mixed metal oxide.

33. A method as claimed in claim 32 wherein the particles of material present in the micellar liquid have a particle size that falls within the range of about lnm to about 250nm.

34. A method as claimed in claim 27 wherein the particles of material are evenly dispersed throughout the micellar liquid that is treated in step (c).

35. A method as claimed in claim 27 wherein the particles of material in the micellar liquid treated in step (c) provide one or more metals for incorporation into the complex metal oxide and the one or more metals from the particles are present in the form of a metal or mixture of metals or metal alloys.

36. A method as claimed in claim 27 wherein the particles of material in the micellar liquid treated in step (c) provide one or more metals for incorporation into the complex metal oxide and the particles of material comprise particles of metal compounds, or a mixture of particles of different metal compounds, or particles containing mixed metal compounds, or mixtures thereof.

37. A method as claimed in claim 36 wherein the particles are in the form of oxides, nitrates, chlorides, sulfates, hydroxides, or oxy-hydrides.

38. A method as claimed in claim 27 wherein step (c) comprises heating of the mixture from step (b) to an elevated temperature to thereby form the metal oxide particles.

39. A method as claimed in claim 38 wherein heating of the mixture form step

(b) is preceded by a step of treating the surfactant/liquid mixture to form a gel.

40. A method as claimed in claim 1 further comprising adding a pore-forming material to the mixture to form a porous complex metal oxide.

41. A method as claimed in claim 27 further comprising adding a pore-forming material to the mixture to form a porous complex metal oxide.