WO2019042910A1 - Oxyde mixte à propriétés redox améliorées - Google Patents

Oxyde mixte à propriétés redox améliorées Download PDF

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Publication number
WO2019042910A1
WO2019042910A1 PCT/EP2018/072962 EP2018072962W WO2019042910A1 WO 2019042910 A1 WO2019042910 A1 WO 2019042910A1 EP 2018072962 W EP2018072962 W EP 2018072962W WO 2019042910 A1 WO2019042910 A1 WO 2019042910A1
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Prior art keywords
mixed oxide
oxide
cerium
base metal
atmosphere
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PCT/EP2018/072962
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English (en)
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Fabien OCAMPO
Naotaka Ohtake
Barry William Luke Southward
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Rhodia Operations
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/10—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of rare earths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
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    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/615—100-500 m2/g
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/10—Heat treatment in the presence of water, e.g. steam
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F17/00—Compounds of rare earth metals
    • C01F17/30—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6
    • C01F17/32—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6 oxide or hydroxide being the only anion, e.g. NaCeO2 or MgxCayEuO
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F17/00—Compounds of rare earth metals
    • C01F17/30—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6
    • C01F17/32—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6 oxide or hydroxide being the only anion, e.g. NaCeO2 or MgxCayEuO
    • C01F17/34—Aluminates, e.g. YAlO3 or Y3-xGdxAl5O12
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C01G25/006—Compounds containing, besides zirconium, two or more other elements, with the exception of oxygen or hydrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/16—Selection of particular materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/206—Rare earth metals
    • B01D2255/2065—Cerium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20761—Copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/209—Other metals
    • B01D2255/2092—Aluminium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/30—Silica
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/60—Compounds characterised by their crystallite size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/85—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by XPS, EDX or EDAX data
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/12—Surface area
    • C01P2006/13—Surface area thermal stability thereof at high temperatures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/90—Other properties not specified above
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2510/00—Surface coverings
    • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to a mixed oxide based upon cerium, an element which is Al or Si and a base metal (BM).
  • the invention also relates to the process of preparation of said mixed oxide and to the use of said mixed oxide for the preparation of a catalytic converter.
  • the invention also relates to a process for the treatment of an exhaust gas released by the internal combusion engine of a vehicle, using said mixed oxide.
  • Catalysts for purifying vehicle exhaust gases are composed of a catalytic metal selected from one or a Platinum Group Metal (or PGM) which is dispersed on a co-catalytic support material to enhance catalytic function.
  • typical support materials include, but are not limited to, high surface area, thermally stable oxides including (doped) alumina, silica, zeolites and (doped) ceria or (doped) ceria-zirconia solid solutions.
  • This PGM promoted support oxide is in turn mixed with promoters or other functional materials to yield the fully formulated catalyst washcoat which is then deposited upon an appropriate ceramic substrate e.g. cordierite, SiC or metallic form. The ceramic or metallic form is then canned and incorporated in the exhaust train to provide the required catalytic conversion of pollutants.
  • cerium oxide-containing materials are present as pure, high surface area cerium oxide e.g. as described in US 7,361 ,322 B2 or as a (doped) ceria-zirconia (CeO 2 -ZrO 2 ) solid solution e.g. as described in US 7,939,040 or US 8,956,994.
  • Cerium oxide is a ubiquitous component of aftertreatment catalysts for gasoline vehicles due to its ability to 'buffer' the active components in the catalyst against local fuel rich (reducing) or fuel lean (oxidising) conditions.
  • Ceria facilitates this buffering or reduction- oxidation (hereafter redox) chemistry by utilisation of the Ce -» Ce redox couple, with the oxidation state of Ce depending upon local O 2 content.
  • Ce 4+ releases active oxygen from its 3-D structure in a rapid and reproducible manner under oxygen-depleted transients, regenerating this 'lost' oxygen by adsorption from the gaseous phase when oxygen rich conditions arise.
  • This high availability of oxygen is critical for the promotion of generic oxidation / reduction chemistries e.g. CO oxidation or NO reduction of the gasoline three-way catalyst.
  • the base metal may be Fe, Cu or Ag.
  • US 2009/0257935 discloses a cerium-zirconium-based mixed oxide modified by a base metal.
  • the compositions disclosed comprise zirconium.
  • US 8,858,903 discloses a layer (overcoat 106) which includes at least copper oxide, ceria, alumina, and optionally one oxygen storage material.
  • the amount of ceria is at most 50 wt%.
  • US 7,329,627 discloses a mixed oxide based on cerium, lanthanum, copper and manganese. Cu can be partially substituted with Co, Fe, Ni and/or Zn. The compositions disclosed do not comprise Al or Si.
  • US 8,479,493 discloses the combination of particles of a mixed oxides of Ce, Zr, and Cu with particles of at least one PGM catalyst dispersed on particles of aluminum oxide (AI2O3).
  • the combination requires the use of zirconium.
  • Journal of Catalysis 2010, 272, 109-120 discloses in general terms a catalyst CeO2-CuO on a ⁇ - ⁇ 2 03 prepared by impregnation with precursors Cu(NOs)2 and Ce(NO3) 4 on AI2O3 as a support.
  • the proportion of aluminium exceeds the proportion of claim 1 .
  • WO 2013/163536 discloses in example 1 of Table 1 an impregnated catalyst containing an equivalent of 5 wt% MnO 2 , 10 wt% CuO on ceria and 3 wt% of an alumina binder. There is no disclosure of a specific surface area of at least 35 m 2 /g after being ageing at 800°C for 16 hours under a atmosphere composed of 10.0% O 2 / 10.0% H 2 O / balance of N 2 .
  • Fig. 1 provides the TPR curves of the mixed oxides of example 6 (5.0% CuO on CeO 2 ) and of example 2 (5.0% CuO on CeAI).
  • Fig. 2 provides the TPR curves of the mixed oxides of example 8 (5.0% CuO on CZ-1 ) and of example 10 (5.0% CuO on CZ-2).
  • Fig. 3 provides the diffractograms of the mixed oxides of example 8 (5.0% CuO on CZ-1 ), of example 6 (5.0% CuO on CeO 2 ) and of example 2 (5.0% CuO on CeAI) after aging under hydrothermal conditions (800°C / 16 h).
  • Fig. 4 provides the diffractograms of the mixed oxides of example 8 (5.0% CuO on CZ-1 ), of example 6 (5.0% CuO on CeO 2 ) and of example 2 (5.0% CuO on CeAI) after aging under lean/rich conditions (720°C / 8 h).
  • the invention relates to a mixed oxide of cerium, of an element which is aluminium or silicon and a base metal (BM) selected from Fe, Co, Ni or an element of groups 5, 6, 7 and 1 1 of the periodic table, with the following proportions:
  • aluminium or silicon up to 20.0%
  • ⁇ base metal up to 15.0%
  • the mixed oxide of the invention is based upon the above mentioned elements with the above mentioned proportions.
  • the mixed oxide may thus be described by the generic formula Cei-( y+Z ) (Al or Si) y (BM) Z O a wherein:
  • ⁇ y is the proportion of Al or Si
  • ⁇ z is the proportion of the base metal
  • ⁇ a is the stoechiometric balance in oxygen in the mixed oxide
  • the base metal may more particularly be Fe, Co, Ni or Cu.
  • a particular preferred base metal is Cu. More particularly, when the base metal is Cu, no other base metal like from Fe, Co, Ni or an element of groups 5, 6, 7 and 1 1 is present in the mixed oxide. In particular, when the base metal is Cu, the mixed oxide does not comprise Mn and/or Fe.
  • the above mentioned elements Ce, Al, Si, BM that constitute the mixed oxide are present in the mixed oxide as oxides. According to an embodiment, they may nonetheless be also partially present in the form of hydroxides or oxyhydroxides. Their proportions are given by weight of the corresponding oxide (CeO2, AI2O3 or S1O2, oxide of the base metal) with respect to the total weight of the mixed oxide and are expressed as wt%. The proportions of each of these elements are determined by the usual analytical methods like X-ray fluorescence which are known to a person skilled in the art. An XRF spectrometer PANalytical Axios-Max may for instance be used.
  • the oxide to be retained for the calculation of the proportions corresponds to the most common and thermodynamically stable oxide at ambiant temperature and ambiant pressure of the highest oxidation number.
  • oxides are given: Fe 2 O 3 , Co 3 O 4 , MnO 2 , CuO, NiO.
  • the mixed oxide contains aluminium or silicon which are present respectively in the form of aluminium oxide or of silicon oxide, y is up to 20.0%. y may more particularly be between 0.1 % and 19.8%, more particularly between 1 .0% and 10.0%, even more particularly between 2.0% and 6.0% or between 4.0% and
  • the mixed oxide contains also a base metal which is selected from Fe, Co, Ni or an element of group 5, 6, 7 and 1 1 of the periodic table, more particularly Cu.
  • z is up to 15.0%. z may be between 0.5% and 10.0%, more particularly between 1 .0% and 8.0%, even more particularly between 4.0% and 8.0% or between 4.0% and 6.0%.
  • the mixed oxide contains also cerium which is present in the form of cerium oxide.
  • Cerium oxide is the predominant oxide of the mixed oxide. This is to say that the proportion by weight of cerium oxide is superior to each proportion by weight of each other oxide.
  • the proportion of cerium (or 1 -(y+z) in the above formula) in the mixed oxide may be at least 68.0%, more particularly of at least 80.0%, even more particularly of at least 85.0% or of at least 90.0%.
  • the proportion of cerium in the mixed oxide may be between 68.0% and 98.9%, more particularly between 86.0% and 94.0% or between 88.0% and 94.0%.
  • a mixed oxide according to the invention may thus comprise:
  • aluminium or silicon between 2.0% and 6.0%;
  • the base metal between 4.0% and 8.0%, more particularly between 4.0% and 6.0%;
  • ⁇ cerium between 86.0% and 94.0%, more particularly between 88.0% and 94.0%.
  • the mixed oxide may also comprise:
  • aluminium or silicon between 2.0% and 6.0%;
  • ⁇ the base metal between 4.0% and 6.0%;
  • ⁇ cerium between 88.0% and 94.0%.
  • the mixed oxide of the invention may also additionally comprise impurities.
  • the impurities may stem from the raw materials or starting materials used in the process of preparation of the mixed oxide.
  • the total proportion of the impurities is generally lower than 0.3% by weight, more particularly lower than 0.1 %, with respect to the mixed oxide as a whole.
  • the proportions of the impurities may be determined with an Inductively Coupled Plasma Mass Spectrometry.
  • the mixed oxide of the invention may also consist of cerium oxide, of an oxide of an element which is aluminium or silicon and an oxide of a base metal (BM) selected from Fe, Co, Ni or an element of groups 5, 6, 7 and 1 1 of the periodic table, and optionally of impurities, with the following proportions:
  • aluminium or silicon up to 20.0%
  • ⁇ base metal up to 15.0%
  • the mixed oxide of the invention may also consist essentially of cerium oxide, of an oxide of an element which is aluminium or silicon and an oxide of a base metal (BM) selected from Fe, Co, Ni or an element of groups 5, 6, 7 and 1 1 of the periodic table, with the following proportions:
  • BM base metal
  • aluminium or silicon up to 20.0%
  • ⁇ base metal up to 15.0%
  • the mixed oxide of the invention may be prepared by impregnation of a mixed oxide of cerium and aluminium (CeAI) or of cerium and silicon (CeSi) with an aqueous solution of a precursor of the oxide of the base metal.
  • This technique consists in filling the porous volume of the mixed oxide CeAI or CeSi with an aqueous solution of a precursor of the oxide of the base metal, drying the resulting mixture and calcining in air the resulting mixture at a temperature of at least 400°C, more particularly between 400°C and 800°C.
  • the temperature calcination temperature may be comprised between 400°C and 800°C.
  • the temperature of calcination should be high enough to convert the elements Ce, Al, Si and BM into oxides.
  • the duration of the calcination may be comprised between 0.5 h and 15 h.
  • the precursor of the oxide of the base metal may be a salt or a coordination compound of the base metal which is soluble in water.
  • the salt of the base metal may for instance be a chloride, a nitrate or an acetate.
  • the coordination compound of the base metal may be an acetonate.
  • An example of salt is copper (II) nitrate trihydrate.
  • the impregnation technique may be more particularly an incipient wetness impregnation technique (also known as 'dry impregnation'). This technique is well-known to a person skilled in the art.
  • step (i) filling the pores of the mixed oxide CeAI or CeSi in the form of a powder with an aqueous solution of the precursor of the oxide of the base metal; (ii) in drying the solid obtained at the end of step (i) and (iii) in calcining in air the solid obtained at the end of step (ii) at a temperature of at least 400°C.
  • the temperature of calcination of step (iii) should be high enough to convert the elements Ce, Al, Si and BM into oxides.
  • the volume of the aqueous solution of the precursor having the appropriate concentration is equal or slightly lower than the pore volume of the mixed oxide CeAI or CeSi.
  • the volume of the aqueous solution is substantially the same as the volume of water added to the mixed oxide CeAI or CeSi to be impregnated before it visually appears wet.
  • the impregnation of the solid and the determination of the water added are performed with a continuous addition of respectively the aqueous solution of the base metal or of water.
  • the incipient wetness impregnation technique may be performed according to the method which involves the following steps and which is used for the preparation of the mixed oxide of examples 1 -5:
  • fire loss 1 - (weight of mixed oxide after calcination / weight of mixed oxide prior to calcination). The calcination used for the determination of the fire loss is performed at 160°C.
  • the retention volume of water of the mixed oxide CeAI or CeSi is the volume of water that the mixed oxide can adsorb inside its porosity before liquid water can be observed between the particles of the powder.
  • the retention volume is usually close to the porous volume.
  • the retention volume is given in ml_ of water per g of mixed oxide CeAI or CeSi and is determined at 20°C / 1 atm.
  • the weight m may be from 10.0 g to 30.0 g;
  • V r v / m
  • the aqueous solution is characterized by a concentration C of the base metal so that after last step 4), the proportion of the base metal in the mixed oxide genuinely corresponds to the desired proportion (P%) of the base metal in the mixed oxide:
  • cP% is the corrected proportion which is given by the formula below:
  • V volume of the aqueous solution of the precursor to be used for the impregnation
  • ml_ volume of the aqueous solution of the precursor to be used for the impregnation
  • M is the weight of the mixed oxide CeAI or CeSi to be impregnated.
  • the precursor is weighted and dissolved in water to obtain the aqueous solution of the precursor.
  • the precursor is commercialized as a solution, the volume of the solution is determined and the solution is mixed with water to obtain the aqueous solution of the precursor. In that case, it is preferable to use a solution, the concentration of which is certified.
  • step 2) impregnation of the mixed oxide CeAI or CeSi with the aqueous solution of the base metal and drying: the impregnation is performed in conditions that are identical to the conditions of step 2):
  • the aqueous solution of the precursor (volume Vi) is added drop by drop onto the mixed oxide (weight M) CeAI or CeSi to be impregnated; - the mixture is kept being homogeneized during 30 min at room temperature;
  • the dried solid is then calcined in air in a furnace at 500°C for 2 hours.
  • the incipient wetness impregnation may also be performed automatically using an automatic appliance developed by Chemspeed Technologies AG (see https://w ww.chemspeed.com/videopaae/incipient-wetness-impreanation/). In that case, steps 1 ) to 3) disclosed above may be used similarly with the automatic appliance.
  • the mixed oxide CeAI or CeSi used exhibits a total pore volume of at least 0.30 mL/g.
  • the total pore volume may be comprised between 0.30 and 2.0 mL/g, more particularly between 0.50 and 1 .5 mL/g.
  • the porosity is measured by mercury intrusion according to the well-known techniques in the field.
  • the mixed oxide CeAI or CeSi is an intimate mixture of the oxides of Ce and Al or of Ce and Si.
  • the process of preparation disclosed below makes it possible to obtain such an intimate mixture on an atomic level.
  • the oxide of the base metal is dispersed on the surface of the mixed oxide CeAI or CeSi.
  • the invention thus also more particularly relates to a mixed oxide of cerium and aluminium or of cerium and silicon on which the oxide of the base metal is dispersed.
  • the proportions of cerium and aluminium or silicon in the mixed oxide CeAI or CeSi may be the following :
  • aluminium or silicon up to 20.0%
  • the mixed oxide CeAI or CeSi may also additionaly comprise impurities. These impurities may stem from the raw materials or starting materials used in the process of preparation of the mixed oxide CeAI or CeSi.
  • the total proportion of the impurities is generally lower than 0.3 wt%, more particularly lower than 0.1 wt%, with respect to the mixed oxide CeAI or CeSi as a whole.
  • the proportions of the impurities may be determined with an Inductively Coupled Plasma Mass Spectrometry.
  • the mixed oxide of the invention is characterized by its thermal resistance in classical conditions. It may thus exhibit a specific surface area of at least 70 m 2 /g, more particularly of at least 80 m 2 /g after calcination in air at 800°C for 2 hours.
  • the specific surface area after calcination in air at 800°C for 2 hours may range from 70 to 130 m 2 /g, more particularly from 80 to 130 m 2 /g. It may also exhibit a specific surface area of at least 40 m 2 /g, more particularly of at least 60 m 2 /g after calcination in air at 900°C for 5 hours.
  • the specific surface area after calcination in air at 900°C for 5 hours may range from 40 to 85 m 2 /g, more particularly from 60 to 85 m 2 /g. It may also exhibit a specific surface area of at least 20 m 2 /g, more particularly of at least 40 m 2 /g after calcination in air at 1000°C for 5 hours.
  • the specific surface area after calcination in air at 1000°C for 5 hours may range from 20 to 55 m 2 /g, more particularly from 40 to 55 m 2 /g.
  • the mixed oxide may be also characterized by its resistance in more severe conditions ('hydrothermal' conditions and/or 'lean/rich' conditions) which are now detailed below.
  • the mixed oxide is aged at 800°C for 16 hours in an atmosphere composed of 10.0 vol% O2 / 10.0 vol% H 2 O / the balance being N 2 .
  • the expression 'balance being N 2 ' means that the balance to 100.0 vol% of the atmosphere is made of N 2 .
  • this atmosphere is thus of the following composition: 10.0 vol% O 2 / 10.0 vol% H 2 O and 80.0 vol% N 2 .
  • the mixed oxide exhibits a specific surface area of at least 35 m 2 /g, more particularly of at least 40 m 2 /g.
  • the hydrothermal conditions may be as detailed in the examples.
  • the specific surface under these conditions may range from 35 to 55 m 2 /g, more particularly from 48 to 55 m 2 /g.
  • the specific surface areas are determined by adsorption of nitrogen by the Brunauer-Emmett-Teller method (BET method). The method is disclosed in standard ASTM D 3663-03 (reapproved 2015). The method is also described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)". The specific surface areas are expressed for specific conditions of temperature, time and atmosphere. The specific surface areas are determined with an appliance Flowsorb II 2300 of Micromeritics according to the guidelines of the constructor. Prior to the measurement, the samples are degassed under static air by heating at a temperature of at most 200°C to remove the adsorbed species. Conditions may be found in the examples. 'lean-rich' conditions
  • the mixed oxide is also resistant under 'lean-rich' conditions.
  • the mixed oxide is aged at 720°C for 8 hours in an atmosphere which is alternatively:
  • the mixed oxide is placed at 720°C for 8 hours in an atmosphere which alternates between A1 for 90 s and A2 for 90 s.
  • the cycle is applied during 8 hours and is thus the following : A1 (90 s), A2 (90 s), A1 (90 s), A2 (90 s),... (note that the cycle may start either with A1 or with A2 without any impact). By doing so, the atmosphere switches alternatively from A1 to A2 and vice versa.
  • the cycle is operated for 8 hours.
  • the 'lean/rich' conditions which are applied may be as detailed in the examples.
  • the mixed oxide After such treatment under the cycles A1 - A2, the mixed oxide exhibits a specific surface area of at least 35 m 2 /g, more particularly of at least 40 m 2 /g.
  • the specific surface under these conditions may range from 35 to 55 m 2 /g, more particularly from 40 to 55 m 2 /g. more severe 'lean-rich' conditions
  • the mixed oxide is also resistant under an even more severe 'lean-rich' aging. Indeed, when the mixed oxide is aged at 800°C for 16 hours in an atmosphere which is alternatively:
  • the conditions of the method of preparation of the mixed oxide and used in the examples have made it possible to obtain a good dispersion of the oxide of the base metal on the CeAI or CeSi mixed oxide.
  • the oxide of the base metal is such that is not detectable by X-ray powder diffraction (XRD).
  • the diffractogram of the mixed oxide obtained by XRD does not exhibit any reflexion in the range 2 ⁇ between 38.0° and 40.0°. This means that the intensity of the signal of the detector is of the same order as the intensity of signal of the baseline.
  • the oxide of the base metal is dispersed on the surface of the mixed oxide of cerium and aluminium or of cerium and silicon in the form of a substoichiometric oxide of the base metal.
  • the oxide of copper may be described by formula CuO p with ⁇ 1 .
  • the dispersion remains stable even after the 'hydrothermal' conditions (800°C / 16 hours / atmosphere composed of 10.0 vol% O 2 / 10.0 vol% H 2 O / the balance being N 2 ) or the 'lean/rich' conditions (720°C / 8 hours / atmosphere alternating between A1 and A2) that are detailed above.
  • the diffractogram of the mixed oxide does not exhibit any reflexion (or peak) in the range 2 ⁇ between 38.0° and 40.0° after these agings under either the 'hydrothermal' or 'lean/rich' conditions.
  • the mixed oxide of the invention may also exhibit good reducibility properties. These properties such as T max and T en d are determined by the temperature- programmed reduction (TPR) measurement method.
  • TPR temperature- programmed reduction
  • This method consists in measuring the consumption of hydrogen of the mixed oxide of the invention while being heated, as a function of temperature.
  • the hydrogen consumption is measured with a conductivity thermal detector (TCD) while the mixed oxide is heated from 20°C to 900°C with an increase ramp of 10°C/min under a reducing atmosphere composed of Ar (90.0 vol%) and H 2 (10.0 vol%).
  • TCD conductivity thermal detector
  • the measurement can be performed with a Micromeritics Autochem 2920 machine.
  • the TPR curve gives the intensity of the signal (y axis) of the TCD as a function of the temperature of the sample (x axis).
  • the TPR curve is the curve from 20°C to 900°C.
  • Tmax is defined as the temperature for which the intensity of the signal of the TCD is maximum on the TPR curve.
  • the raw signal of the TCD is negative, it is standard to plot the opposite of the raw signal so that the TPR curve contains peaks with maximum values.
  • the mixed oxide of the invention may exhibit a T max ranging from 1 15°C to 140°C. Without being bound by any theory, the T max observed may be assigned to a species based on the BM.
  • ⁇ Tend corresponds to the first temperature at which the signal of the TCD returns to the baseline.
  • the mixed oxide of the invention may exhibit a T en d lower than 215°C, more particularly lower than 200°C.
  • the intensity of the signal of the TCD may not return to the value yo. In this case, the signal is nonetheless considered to return to the baseline when the intensity of the signal of the TCD returns to a value equal to yo+5%.
  • the width at half height of the peak of the signal at T max is generally lower than 30°C, more particularly lower than 25°C, even more particularly lower than 15°C. It is generally considered that the more narrow the peak at T max , the better the dispersion of the reducible species. It is also observed that the average size t of the crystallites of cerium oxide may be lower than 20 nm, more particularly lower than 19 nm after the mixed oxide is aged at 800°C for 16 hours in a atmosphere composed of 10.0 % O 2 / 10.0 % H 2 O / balance of N 2 . The average size t of the crystallites of cerium may also be lower than 20 nm, more particularly lower than 19 nm after the mixed oxide is aged at 720°C for 8 hours in an atmosphere which is alternatively:
  • This average size t is determined with the use of the Scherer formula from an X- ray powder diffraction pattern obtained by standard techniques.
  • the Scherer formula below gives the aver
  • H width of the peak at half height of the considered reflexion
  • ⁇ Bragg angle.
  • the average size t is based on the most intense reflexion.
  • the mixed oxide CeAI may be prepared by the method disclosed in example 6 of EP 444470.
  • the mixed oxide CeSi may be prepared by the method disclosed in US 5,529,969.
  • the mixed oxide CeAI or CeSi may also be prepared by the preferred method disclosed below:
  • an aqueous solution of a basic compound may optionally be added to adjust the pH of the mixture to at least 7.0, more particularly between 8.0 and 9.0;
  • DR decrease ratio
  • [NO3 " ]ste P b is concentration in mol/L of the nitrate anions in the liquid medium of the suspension obtained at the end of step (b).
  • the preferred method involves the use of an aqueous solution of Ce lv and optionally Ce'" cations characterized by a molar ratio Ce lv /total cerium of at least 0.9. This ratio may be 1 .0. It is advantageous to use a salt of cerium with a purity of at least 99.5%, more particularly of at least 99.9%.
  • An aqueous eerie nitrate solution can for instance be obtained by reaction of nitric acid with an hydrated eerie oxide prepared conventionally by reaction of a solution of a cerous salt and of an aqueous ammonia solution in the presence of aqueous hydrogen peroxide to convert Ce'" cations into Ce lv cations. It is also particularly advantageous to use a eerie nitrate solution obtained according to the method of electrolytic oxidation of a cerous nitrate solution as disclosed in FR 2570087.
  • the water used to prepare the aqueous solution is preferably deionized water.
  • the concentration of cerium expressed in terms of cerium oxide in the aqueous solution of cerium may be comprised between 5 and 150 g/L, more particularly between 30 and 60 g/L.
  • concentration in terms of oxide a concentration of 225 g/L of nitrate of cerium corresponds to 100 g/L of CeO2.
  • the amount of H + in the aqueous solution of cerium of Ce lv and optionally Ce'" cations used in step (a) may be between 0.01 and 1 .0 N, more particularly between 0.05 and 0.20 N.
  • the acidity of the aqueous solution used in step (a) may be adjusted by the addition of HNO3 and/or NH 3 (in the case of the addition of NH3, the quantity of base added is just necessary to adjust the acidity without there being any precipitation).
  • the aqueous solution used in step (a) may exhibit an acidity around 0.12 N, as in example A.
  • a typical aqueous solution of cerium contains Ce lv , optionally Ce'", H + and NO3 " .
  • the aqueous solution may be obtained by mixing the appropriate quantities of nitrate solutions of Ce lv and Ce'" and by optionally adjusting the acidity.
  • the aqueous solution of cerium is heated and held at a temperature between 60°C and 170°C, more particularly between 90°C and 160°C, so as to obtain a suspension comprising a liquid medium and a precipitate.
  • the precipitate may be in the form of cerium hydroxide.
  • Any reaction vessel may be used in step (a) without critical limitation, and either a sealed vessel or an open vessel may be used. Specifically, an autoclave reactor may preferably be used.
  • the duration of the heat treatment is usually between 10 min and 48 hours, preferably between 30 min and 36 hours, more preferably between 1 hour and 24 hours.
  • the function of this heating step is to improve the crystallinity of the precipitate which results in a better heat resistance of the mixed oxide.
  • the conditions used in the examples may be applied.
  • step (b) the concentration of the nitrate anions NO3 " present in the liquid medium is decreased by removing a part of the liquid medium from the suspension obtained at the end of step (a). This is performed by leaving the solid of the suspension settle and by removing partly the liquid on the top.
  • the precursor of aluminium oxide or of silicon oxide is added to the suspension.
  • the precursor for CeAI may be aluminium nitrate such as e.g. aluminum nitrate nonahydrate.
  • the precursor for CeSi may be silicon dioxide.
  • the silicon dioxide may in the form of a colloidal dispersion of silicon dioxide in water.
  • the primary particles in the colloidal dispersion may exhibit a size lower than 15 nm.
  • the secondary particles in the colloidal dispersion may exhibit a size lower than 30 ⁇ .
  • An example of suitable colloidal dispersion is Aedlite AT-20Q commercialized by Adeka Chemical.
  • Water may also be added to adjust the total volume.
  • the amount of the precursor added depends on the targeted composition of the mixed oxide. It must be noted that, when removing some of the liquid from the suspension, some of the solid may be removed as well. In that case, the amount of the precursor to be added is calculated by mass balance to take into account the amount of solid (and hence of cerium) having been so removed.
  • the method is characterized by the decrease of the concentration of nitrate anions NO3 " in the liquid medium of the suspension obtained at the end of step (b) (that is after the removal of part of the liquid medium and the addition of the precursor and optionally water) in comparison to the concentration of NO3 " in the aqueous solution of cerium used in step (a).
  • the decrease may be characterized by a decrease ratio (DR) between 10% and 90%, more particularly between 30% and 50%, even more particularly between 35% and 45%, wherein DR is given by formula (I) :
  • [NO3 " ]ste P a concentration in mol/L of the nitrate anions in the aqueous solution of cerium used in step (a) ;
  • [NO3 " ]ste P b concentration in mol/L of the nitrate anions in the liquid medium of the suspension obtained at the end of step (b) (that is after the removal of part of the liquid medium and the addition of the precursor and optionally of water).
  • DR is given by (F/G)/(D/E) x 100.
  • - C is the quantity of nitrate anions NO 3 " (mol) from other sources than cerium nitrate(s) e.g. the nitrate anions associated with the H + in the solution.
  • the volumes E and G may be measured by a gauge.
  • step (c) the mixture obtained at the end of step (b) is heated.
  • the temperature of the mixture may be from 100°C to 300°C, more particularly from 1 10°C to 150°C.
  • the duration of the heating may be from 10 min to 40 h, more particularly from 30 min to 36 h.
  • the conditions of example A can be applied.
  • step (c') an aqueous solution of a basic compound may be added to adjust the pH of the mixture to at least 7.0, more particularly between 8.0 and 9.0.
  • An aqueous ammonia solution may be added.
  • step (e) the precipitate which is recovered from the mixture obtained at the end of step (c) or at the end of step (c') is optionally dried to remove partly or completely the water which is present.
  • the recovery may be performed by separation of the liquid medium from the precipitate. Filter pressing, decantation or Nutsche filter may be used.
  • the precipitate may optionally be washed with water, preferably water at a pH > 7. An aqueous ammonia solution may be used.
  • step (f) the solid obtained at the end of the step (e) is calcined in air at a temperature between 300°C and 800°C.
  • the duration of the calcination may vary from 1 to 20 hours.
  • the solid may be calcined at a temperature of 500°C for 10 hours.
  • step (g) the solid (mixed oxide) from step (f) may be ground to reduce the size of the solid particles.
  • Use can be made of a hammer mill.
  • the powder may exhibit an average particle size d 5 o between 0.05 and 50.0 ⁇ .
  • d 5 o is obtained from a distribution in volume which is measured by laser diffraction. The distribution may be obtained for instance with a LA-920 particle size analyzed commercialized by Horiba, Ltd.
  • the preparation of CeAI or CeSi may be as disclosed in Examples A or B.
  • a skilled person may adapt the recipes disclosed in these two examples to prepare mixed oxides CeAI or CeSi that exhibit other contents of Ce and Al or Ce and Si. about the use of the mixed oxide of the invention
  • the mixed oxide of the invention may be used in the field of exhaust gas treatment.
  • the mixed oxide of the invention may be used to reduce the amounts of CO and/or unburnt hydrocarbons (HCs) in an exhaust gas released by the internal combusion engine of a vehicle. It may be more particularly used in the preparation of a catalytic converter which is used to treat exhaust gases released by the internal combusion engine of a vehicle.
  • HCs unburnt hydrocarbons
  • the catalytic converter comprises at least one catalytically active layer prepared with the mixed oxide and deposited on a solid support.
  • the function of the layer is to chemically convert some pollutants of the exhaust gas, more particularly CO or unburnt hydrocarbons, into products that are less harmful to the environment.
  • the chemical reactions involved with CO and HCs may be the following :
  • the solid support may be a monolith made of ceramic, for example of cordierite, of silicon carbide, of alumina titanate or of mullite, or of metal, for example Fecralloy.
  • the support is usually made of cordierite exhibiting a large specific surface area and a low pressure drop.
  • the catalytically active layer (also called 'washcoat') is deposited.
  • This layer is made from a composition comprising the mixed oxide of the invention.
  • the composition usually also comprises at least one inorganic material other than the mixed oxide.
  • the inorganic material other than the mixed oxide may be for instance selected in the group of alumina, titanium oxide, zirconium oxide, silicas, spinels, zeolithes, silicoaluminium phosphates, crystalline aluminium phosphates.
  • the composition may also comprise other ingredients like a H 2 S trap; any organic or inorganic modifier to help deposit the composition on the support; colloidal alumina;...
  • Alumina is very often used as one inorganic material.
  • Alumina may optionally comprise a doping element like e.g. lanthanum.
  • the mixed oxide of the invention is already catalytically active without any PGM (see examples 12 and 13). It may be used to chemically convert some pollutants of the exhaust gas, such as CO or HC, into products that are lass harmful to the environment. This means that according to an embodiment, the composition comprising the mixed oxide of the invention may be used to prepare the catalytically active layer without the need to disperse any PGM on said layer.
  • the catalytically active layer may also comprise a DOC in addition to the mixed oxide of the invention.
  • the function of the DOC is to convert CO and HCs into CO 2 and to convert NO into NO 2 .
  • a DOC usually consists of at least one PGM, such as e.g.
  • Pt dispersed on an refractory oxide selected from the group consisting of alumina, silica, titania, zirconia, ceria, silica-alumina, titania-alumina, zirconia-alumina, ceria-alumina, titania-silica, zirconia-silica, zirconia-titania, ceria-zirconia and alumina- magnesium oxide.
  • PGM designates a platinum group metal which is a chemical element selected in the following list: Ru, Rh, Pd, Os, Ir, Pt.
  • the refractory oxide is usually an optionally doped alumina such as La-doped alumina.
  • a combination of two PGMs such as a combination of Pt and Pd, may also be dispersed on the alumina.
  • the invention also relates to a composition comprising the mixed oxide of the invention and a DOC.
  • the dispersion of the PGM on the refractory oxide is well-known to a person skilled in the art.
  • An aqueous solution of a salt of the PGM such as a chloride or a nitrate of the PGM, e.g. Pd(ll) tetraamine nitrate or Pt(ll) tetraamine hydroxide may be added to an aqueous dispersion of the refractory oxide and water is removed to fix the salt on the surface of the refractory oxide.
  • the resulting mixture is then dried and calcined in air at a temperature between 300°C and 800°C.
  • An example of such a method of dispersion of the PGM is disclosed in example 1 of US 7,374,729.
  • the catalytic converter comprises the catalytically active layer without any PGM and an additional catalytically active layer comprising the DOC.
  • the mixed oxide is already catalytically active at low temperatures which is of interest for the chemical conversion of the pollutants at 'low' temperatures.
  • the exhaust gas which enters the catalytic converter is at low temperature and the temperature may not be high enough to activate the conversion of the pollutants.
  • the cold start challenge is especially important in the field of diesel emissions control as the lean compression-ignition cycle of the diesel engine results in significantly lower temperatures of the exhaust gas (e.g. 200°C or more) compared to a conventional 3-way / stoichiometric gasoline exhaust.
  • the invention also relates to a process of treatment of an exhaust gas released by the internal combusion engine of a vehicle, comprising contacting the exhaust gas with the mixed oxide or with a composition comprising the mixed oxide of the invention and optionally at least one inorganic material other than the mixed oxide.
  • the process makes it possible to convert the CO and/or the unburnt hydrocarbons into CO 2 .
  • the exhaust gas may more particularly be produced by a diesel engine.
  • the temperature at which the process operates should preferably be higher than 130°C. Good conversions into CO 2 may be observed in the range 130-200°C. Examples
  • the specific surface areas were determined automatically on a Flowsorb II 2300. Prior to any measurement, the samples are carefully degassed to desorb the adsorbed species. To do so, the samples may be heated at 200°C for 2 hours in a stove, then at 300°C for 15 min in the cell of the appliance.
  • the experimental protocol used for the TPR consists in weighing out around 200.0 mg.
  • the sample is then introduced into a quartz cell containing quartz wool at the bottom.
  • the sample is finally covered with quartz wool and placed in the oven of the appliance (Micromeritis Autochem 2920 machine).
  • the temperature programme used is as follows: temperature rise from 20°C to 900°C with an increase ramp of 10°C/min.
  • the reducing atmosphere is composed of Ar (90.0 vol%) and H 2 (10.0 vol%).
  • the temperature of the sample is measured using a thermocouple placed in the quartz cell, just above the sample.
  • the hydrogen consumption during the reduction phase is deduced by means of the calibration of the variation in thermal conductivity of the gas stream measured at the cell outlet using a TCD.
  • the hydrogen consumption is measured between 20°C and 900°C. The higher this hydrogen consumption, the better the reducibility properties of the sample (redox properties).
  • the TPR curve makes it possible to detect the reductible species that may be present in the mixed oxide.
  • the agings are aimed to reproduce the severe conditions that a catalyst or a mixed oxide faces when in contact with the hot gases in the exhaust line.
  • the aging is operated according to three different protocols that are detailed below.
  • the synthetic gas mixtures are obtained by mixing different gases, and the content of each gas in the total mixture is controlled by mass flow meters.
  • 10.0 g of the solid to be aged (in the powder form) are compacted in the form of a pellet with a diameter of 32 mm by applying a pressure of 8 tons for 2 minutes.
  • the pellet so obtained is deagglomerated in a mortar to provide a fine powder which is sieved so as to retain only the fraction of the powder which passes through a sieve of 250 ⁇ and retained with a sieve of 125 ⁇ .
  • the fraction of the powder (2.2 g) is then placed in a fixed bed reactor and aged at a temperature of 800°C during 16 hours in an atmosphere composed of 10.0 vol% O2 / 10.0 vol% H 2 O / the balance being N 2 flowing through the sample with a volumic flow-rate of 24 L/h (measured at 20°C and 1 atm).
  • 10.0 g of the solid to be aged (in the powder form) are compacted in the form of a pellet with a diameter of 32 mm by applying a pressure of 8 tons for 2 minutes.
  • the pellet so obtained is deagglomerated in a mortar to provide a fine powder which is sieved so as to retain only the fraction of the powder which passes through a sieve of 250 ⁇ and retained with a sieve of 125 ⁇ .
  • the fraction of powder (0.8 g) is placed in a fixed bed reactor and then aged for 8 hours at a temperature of 720°C in an atmosphere which alternates between A1 (90 s) and A2 (90 s).
  • the atmospheres A1 and A2 are obtained by mixing alternatively measured quantities of O 2 or of CO in a gas composed of H 2 O and N 2 .
  • the total volumic flow-rate of A1 or of A2 is 24 L/h (20°C / 1 atm).
  • A2 2.7 vol% CO / 10.0 vol% H 2 O / the balance being N 2 .
  • more severe 'lean/rich' conditions 800°C / 16 hours / atmosphere alternating between A1 and A2
  • the conditions are the same as for LR 720°C/8 h above except for the temperature and the duration of the aging.
  • Example A preparation of a mixed oxide of Ce and Al (CeAI)
  • This example describes a mixed oxide of cerium and aluminum at 95:5 by mass in terms of oxides.
  • An aqueous solution was prepared by mixing 100.0 g in terms of CeO 2 of a eerie nitrate solution with a Ce lv / total Ce ratio > 90 mole % in water and the total volume was adjusted to 2 L with pure water.
  • the acidity of the aqueous solution after the addition of pure water was 0.12 N.
  • the solution was heated to 100°C, held at this temperature for 30 min and allowed to cool down to the room temperature, to thereby obtain a suspension.
  • the removal ratio is 0.46 (0.92 L removed from 2 L).
  • This powder was subjected to quantitative analysis by ICP to determine its composition, which was cerium oxide and aluminum oxide at 95:5 by mass. The results of the characterization of the mixed oxide are shown below :
  • Example B preparation of a mixed oxide of Ce and Si (CeSi)
  • This example describes a mixed oxide of cerium and silicon at 95:5 by mass in terms of oxides.
  • An aqueous solution was prepared by mixing 100 g in terms of CeO2 of a eerie nitrate solution (Ce lv / total Ce > 90 mole %) in water and the total volume was adjusted to 2 L with pure water. The acidity of the aqueous solution after the addition of pure water and HN0 3 was 0.12 N. The solution was heated to 100°C, held at this temperature for 30 min, and allowed to cool down to the room temperature, to thereby obtain a suspension.
  • a DR of 50% was used. This value is based on the following calculations.
  • the removal ratio is 0.5 (1 .0 L removed from 2 L).
  • the suspension containing the precursor of silicon oxide was held at 120°C for 2 hours, allowed to cool, and neutralized to pH 8.5 with an aqueous ammonia to confirm precipitation.
  • the obtained slurry was subjected to solid-liquid separation by Nutsche filtering to obtain a filter cake, which was calcined at 500°C for 10 hours in air to obtain a mixed oxide CeSi in the form of a powder.
  • This mixed oxide powder was subjected to quantitative analysis by ICP to determine its composition, which was cerium oxide (CeO2) and silicon oxide (S1O2) at 95:5 by mass. The results are shown in below :
  • Example 1 dispersion of CuO (2.5%) on support A by the wetness impregnation technique
  • the mixed oxide was prepared according to the incipient wetness impregnation technique with 4 steps previously disclosed.
  • the fire loss of support A was determined at 160°C and is equal to 1 .41 %.
  • the retention volume V r of support A was determined at 20°C and 1 atm by adding water drop by drop onto 20.0 g of support A while the mixture is kept being homogeneized by mixing with a spatula, until water was no longer adsorbed. V r is equal to 0.49 mL/g.
  • An aqueous solution of copper was prepared by dissolving the required quantity of copper (II) nitrate trihydrate in deionized water.
  • Example 2 dispersion of CuO (5.0%) on support A by the wetness impregnation technique
  • the mixed oxide was prepared according to the incipient wetness impregnation technique with 4 steps already disclosed and with the same support A as in example 1 .
  • An aqueous solution of copper (9.8 ml_) was prepared by dissolving copper (II) nitrate trihydrate (3.08 g) in deionized water. The aqueous solution was then added drop by drop onto 20.0 g of support A while the mixture is kept being homogeneized by mixing with a spatula. The mixture was left for 30 minutes at room temperature for homogeneization. The obtained product was then dried in an oven at 120°C overnight and further calcined in a furnace at 500°C for 2 hours.
  • the mixed oxides of these examples were obtained following the same recipe as for example 2 using support A (examples 3-4) or support B (example 5).
  • Example 6 impregnation of CuO (5.0%) on cerium oxide (comparative example)
  • the recipe used in example 1 was used for preparing the mixed oxide of example 6 except that the support consists of cerium oxide prepared according to example 2 of EP 1435338 A1 .
  • This support made of CeO2 does not contain aluminium nor silicon.
  • ⁇ CZ-1 refers to a mixed oxide of cerium, zirconium, lanthanum and praseodymium with the following composition (in terms of oxides):
  • Example 11 evaluation of the dispersion of the oxide of the base metal
  • Diffractograms of Fig. 3 and Fig. 4 were recorded after the aging under respectively 'hydrothermal' conditions or 'lean/rich' conditions.
  • the diffractogram of the mixed oxide of example 2 according to the invention does not exhibit any reflexion in the range 2 ⁇ between 38.0° and 40.0°.
  • a reflexion can be observed in this range on the diffractograms of the mixed oxides of examples 6 and 8. This is also visible with the data in Tables I and II below. These data correspond to the variations of the signal in the range 28.0-40.0°. It can be seen that the variation of the signal for example 2 is much lower than for examples 5 and 6.
  • the evaluation of the dispersion of the oxide of the base metal may also be performed using the scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). This technique makes it possible to obtain high resolution images of the surface topography of the mixed oxide.
  • SEM/EDX energy dispersive X-ray spectroscopy
  • Example 12 testing of the mixed oxide of the invention : evaluation of the mixed oxides in a CO oxidation test - determination of the CO oxidation liqht-offs
  • the CO oxidation performance of three catalysts having been aged at 700°C for 4 hours in an atmosphere composed of 10.0 vol% O2 / 10.0 vol% H 2 O / the balance being N 2 was investigated.
  • powders of the aged catalysts were introduced into a U-shaped down-flow reactor made of quartz (length: 225 mm, internal diameter: 6 mm) and a synthetic gas containing CO (see the composition in Table V) was injected to flow through the bed of catalyst at a GHSV (gas hourly space velocity) of 100,000 h "1 under a total flow rate of 500 mL/min.
  • the weight of powder (350 mg or 120 mg) in the reactor depends on the density of the catalyst and is adapted to reach the targeted GHSV of 100,000 h ⁇ 1 .
  • the composition of the gases leaving the reactor was monitored on line by Fourier Transform InfraRed (FTIR) spectrometer.
  • FTIR Fourier Transform InfraRed
  • the mixed oxide of the invention is active without any PGM (see the low light-off temperatures);
  • the mixed oxide of the invention is more active than traditional catalysts based on PtPd dispersed on a lanthanum-doped alumina (usually used as a DOC catalyst) or on cerium oxide.
  • Example 13 testing of the mixed oxide of the invention : determination of the CO oxidation light-off
  • the mixed oxide of the invention maintains a good catalytical activity (see e.g. the T90s of 139°C and 131 °C or the T50/T60 values); - the mixed oxide of the invention exhibits a better catalytical activity than mixed oxides based on Cu oxide dispersed on cerium oxide (without aluminium) or on CZ-mixed oxides (with zirconium and without aluminium);
  • the mixture of the mixed oxide of example 6 and of an alumina referenced as MI-307 results in a material of similar global composition as the mixed oxide of example 2. Yet, the catalytical activity of the mixture is not as good as for the mixed oxide of example 2.
  • the proportion of the base metal like Cu is expressed by weight of oxide with respect to the total weight of the mixed oxide; 2.5% Cu on CeAI thus means that the mixed oxide contains 2.5% of CuO

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Abstract

La présente invention concerne un oxyde mixte à base de cérium, un élément Al ou Si et un métal de base (MB). L'invention concerne également le procédé de préparation dudit oxyde mixte et l'utilisation dudit oxyde mixte pour la préparation d'un convertisseur catalytique. L'invention concerne également un procédé de traitement d'un gaz d'échappement libéré par le moteur à combustion interne d'un véhicule utilisant ledit oxyde mixte.
PCT/EP2018/072962 2017-08-29 2018-08-27 Oxyde mixte à propriétés redox améliorées WO2019042910A1 (fr)

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Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2570087A1 (fr) 1984-09-13 1986-03-14 Rhone Poulenc Spec Chim Procede d'oxydation electrolytique et ensemble d'electrolyse pour sa mise en oeuvre
EP0444470A1 (fr) 1990-02-23 1991-09-04 W.R. Grace & Co.-Conn. Oxyde cérique à haute surface spécifique
US5529969A (en) 1991-12-09 1996-06-25 Rhone-Poulenc Chimie B.E.T. specific surface-stabilized ceria
EP1435338A1 (fr) 2001-09-07 2004-07-07 Anan Kasei Co., Ltd Oxyde cerique et procede de production de celui-ci, ainsi que catalyseur destine a l'epuration des gaz d'echappement
US7329627B2 (en) 2002-11-08 2008-02-12 Sud-Chemie Ag Ce/Cu/Mn-catalysts
US7374729B2 (en) 2004-03-30 2008-05-20 Basf Catalysts Llc Exhaust gas treatment catalyst
US20090257935A1 (en) 2008-03-27 2009-10-15 Southward Barry W L Base metal and base metal modified diesel oxidation catalysts
US20100197479A1 (en) 2009-01-30 2010-08-05 Southward Barry W L Basic exchange for enhanced redox os materials for emission control applications
WO2011039761A2 (fr) * 2009-07-20 2011-04-07 Council Of Scientific & Industrial Research Pérovskites des cealo3 contenant un métal de transition
US7939040B2 (en) 2003-09-04 2011-05-10 Rhodia Operations Composition based on cerium oxide and on zirconium oxide having a high reducibility and high specific surface, methods for the preparation thereof and use as a catalyst
US8479493B2 (en) 2011-05-19 2013-07-09 GM Global Technology Operations LLC Oxidation catalysts for engines producing low temperature exhaust streams
WO2013163536A1 (fr) 2012-04-26 2013-10-31 Basf Corporation Composition de catalyseur à métal de base et procédés de traitement des gaz d'échappement d'une motocyclette
US8858903B2 (en) 2013-03-15 2014-10-14 Clean Diesel Technology Inc Methods for oxidation and two-way and three-way ZPGM catalyst systems and apparatus comprising same
US8956994B2 (en) 2010-05-06 2015-02-17 Rhodia Operations Composition containing oxides of zirconium, cerium and at least one other rare earth and having a specific porosity, method for preparing same and use thereof in catalysis

Patent Citations (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2570087A1 (fr) 1984-09-13 1986-03-14 Rhone Poulenc Spec Chim Procede d'oxydation electrolytique et ensemble d'electrolyse pour sa mise en oeuvre
EP0444470A1 (fr) 1990-02-23 1991-09-04 W.R. Grace & Co.-Conn. Oxyde cérique à haute surface spécifique
US5529969A (en) 1991-12-09 1996-06-25 Rhone-Poulenc Chimie B.E.T. specific surface-stabilized ceria
EP1435338A1 (fr) 2001-09-07 2004-07-07 Anan Kasei Co., Ltd Oxyde cerique et procede de production de celui-ci, ainsi que catalyseur destine a l'epuration des gaz d'echappement
US7361322B2 (en) 2001-09-07 2008-04-22 Anan Kasei Co., Ltd. Ceric oxide and method for production thereof, and catalyst for exhaust gas clarification
US7329627B2 (en) 2002-11-08 2008-02-12 Sud-Chemie Ag Ce/Cu/Mn-catalysts
US7939040B2 (en) 2003-09-04 2011-05-10 Rhodia Operations Composition based on cerium oxide and on zirconium oxide having a high reducibility and high specific surface, methods for the preparation thereof and use as a catalyst
US7374729B2 (en) 2004-03-30 2008-05-20 Basf Catalysts Llc Exhaust gas treatment catalyst
US20090257935A1 (en) 2008-03-27 2009-10-15 Southward Barry W L Base metal and base metal modified diesel oxidation catalysts
US20100197479A1 (en) 2009-01-30 2010-08-05 Southward Barry W L Basic exchange for enhanced redox os materials for emission control applications
WO2011039761A2 (fr) * 2009-07-20 2011-04-07 Council Of Scientific & Industrial Research Pérovskites des cealo3 contenant un métal de transition
US8956994B2 (en) 2010-05-06 2015-02-17 Rhodia Operations Composition containing oxides of zirconium, cerium and at least one other rare earth and having a specific porosity, method for preparing same and use thereof in catalysis
US8479493B2 (en) 2011-05-19 2013-07-09 GM Global Technology Operations LLC Oxidation catalysts for engines producing low temperature exhaust streams
WO2013163536A1 (fr) 2012-04-26 2013-10-31 Basf Corporation Composition de catalyseur à métal de base et procédés de traitement des gaz d'échappement d'une motocyclette
US8858903B2 (en) 2013-03-15 2014-10-14 Clean Diesel Technology Inc Methods for oxidation and two-way and three-way ZPGM catalyst systems and apparatus comprising same

Non-Patent Citations (6)

* Cited by examiner, † Cited by third party
Title
"Multi-component zirconia-titania mixed oxides: catalytic materials with unprecedented performance in the selective catalytic reduction of NO with NH after harsh hydrothermal ageing", APPL. CATAL. B, vol. 105, 2011, pages 373 - 376
BASHIR AHMAD DAR ET AL: "Ceria-Based Mixed Oxide Supported CuO: An Efficient Heterogeneous Catalyst for Conversion of Cellulose to Sorbitol", GREEN AND SUSTAINABLE CHEMISTRY : GSC, SCIENTIFIC RESEARCH PUBL. INC, US, vol. 5, no. 1, 1 January 2015 (2015-01-01), pages 53954 - 1, XP009503128, ISSN: 2160-6951, [retrieved on 20150211], DOI: 10.4236/GSC.2015.51003 *
GREEN AND SUSTAINABLE CHEMISTRY, vol. 5, no. 1, 2015, pages 15 - 24
JOURNAL OF CATALYSIS, vol. 272, 2010, pages 109 - 120
THE JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 60, 1938, pages 309
WU X ET AL: "Simultaneous removal of soot and NO over thermal stable Cu-Ce-Al mixed oxides", CATALYSIS COMMUNICATIONS, ELSEVIER, AMSTERDAM, NL, vol. 9, no. 14, 30 August 2008 (2008-08-30), pages 2428 - 2432, XP023904999, ISSN: 1566-7367, [retrieved on 20080620], DOI: 10.1016/J.CATCOM.2008.06.007 *

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