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  • 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
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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
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
  • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
• • 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
  • C01F17/20—Compounds containing only rare earth metals as the metal element
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  • C01F17/00—Compounds of rare earth metals
  • C01F17/20—Compounds containing only rare earth metals as the metal element
  • C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
  • C01F17/224—Oxides or hydroxides of lanthanides
  • C01F17/235—Cerium oxides or hydroxides
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  • C01G19/00—Compounds of tin
  • C01G19/02—Oxides
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  • B01D—SEPARATION
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  • B01D2255/00—Catalysts
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  • B01D2255/2065—Cerium
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D—SEPARATION
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  • B01D2255/40—Mixed oxides
  • B01D2255/407—Zr-Ce mixed oxides
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  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/066—Zirconium or hafnium; Oxides or hydroxides thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • 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
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  • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
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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
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  • B01J35/613—10-100 m2/g
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  • C01P2006/13—Surface area thermal stability thereof at high temperatures
• • 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
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• • 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
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  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the present invention relates to a composition based on zirconium, cerium and tin oxides, its preparation and its use as a catalyst.
• multifunctional catalysts are used for the treatment of exhaust gases from internal combustion engines (automotive post-combustion catalysis).
• Multifunctional means catalysts capable of carrying out not only the oxidation in particular of carbon monoxide and of the hydrocarbons present in the exhaust gases but also the reduction in particular of the nitrogen oxides also present in these gases (catalysts "three ways").
• Zirconium oxide and cerium oxide appear today as two particularly important and interesting constituents for this type of catalyst. To be effective, these catalysts must have a sufficient specific surface even at high temperature. Another quality required for these catalysts is reducibility.
• reducibility is meant, here and for the rest of the description, the capacity of the catalyst to be reduced in a reducing atmosphere and to be reoxidized in an oxidizing atmosphere.
• This reducibility can be measured by the capacity to capture hydrogen. It is due to cerium in the case of compositions of the known type, the cerium having the property of reducing or oxidizing.
• This reducibility and therefore the efficiency of the catalyst are maximum at a temperature which is currently quite high for known catalysts. This temperature is generally of the order of 600 ° C. However, there is a need for catalysts for which this temperature is lowered or even more generally for which, at a given lower temperature, the reducibility is increased.
• the object of the invention is therefore the development of a catalyst with improved reducibility at low temperature.
• composition of the invention is based on zirconium oxide and on cerium oxide and it is characterized in that it contains tin oxide in a proportion of at most 25% by mass of oxide.
• specific surface is understood to mean the BET specific surface determined by nitrogen adsorption in accordance with standard ASTM D 3663-78 established on the basis of the BRUNAUER method -
• Rare earth is understood to mean ryttrium and the elements of the group consisting of the elements of the periodic classification with atomic number between 57 and 71 inclusive. , unless otherwise indicated, in the ranges of values which are given, the terminal values are included The contents are given in oxides unless otherwise indicated Cerium oxide is in the form of ceric oxide (CeO 2 ). tin oxide is in the form of stannic oxide (SnO 2 ).
• Cerium oxide is in the form of ceric oxide (CeO 2 ).
• tin oxide is in the form of stannic oxide (SnO 2 ).
• the compositions of the invention are presented according to two embodiments which differ in the nature of their basic constituents, other than tin. , these compositions are based on zirconium oxide and on cerium oxide.
• the composition does not contain any other oxide of another element which may be a constituent element of this composition and / or a stabilizer. some on face of it in the form of a rare earth other than cerium.
• the compositions are based on cerium oxide, on zirconium oxide and they also contain at least one rare earth oxide other than cerium. In this case, therefore, these are compositions which contain, in addition to tin oxide, at least three and, optionally, four other oxides, or even more.
• the rare earth other than cerium can in particular be chosen from yttrium, lanthanum, neodymium and praseodymium, lanthanum and neodymium being preferred.
• the content, expressed by mass of the rare earth oxide other than cerium relative to the mass of the entire composition is generally at most 35%, in particular not more than 15%, more particularly not more than 10%.
• the compositions for which the contents of rare earth other than cerium are the highest are preferably those for which at least one of these rare earths other than cerium is praseodymium.
• the respective proportions of zirconium oxide and cerium oxide can vary over a wide range regardless of the embodiment. Preferably, these proportions are such that the Ce / Zr molar ratio is between 0.10 and 4, more particularly between 0.15 and 2.25 and even more particularly between 0.2 and 1.20.
• the main characteristic of the compositions of the invention is the presence of tin oxide.
• the content of this oxide expressed by mass of oxide (SnO 2 ) relative to the mass of the entire composition is at most 25%. This content is more particularly at most 20%. It can be at most 10% and even more particularly at most 5%.
• the minimum tin content is that below which there is no longer any effect on the reducibility of the composition. This effect, as will be seen below, can result in the presence of a reducibility peak at a low temperature, below 500 ° C. Generally, this tin content is at least 0.5%, more particularly at least 1%.
• the compositions of the invention may optionally be in the form of a pure solid solution. The nature of this solid solution varies as a function of the Ce / Zr ratio.
• these compositions in which the cerium, the tin and, where appropriate, the other rare earth element are present completely in solid solution in zirconium.
• the X-ray diffraction spectra of these compositions reveal in particular, within these, the existence of a single phase clearly identifiable and corresponding to that of a zirconium oxide crystallized in the tetragonal system with a shift of the mesh parameters , thus reflecting the incorporation of cerium, tin and the other element in the crystal lattice of zirconium oxide, and therefore obtaining a true solid solution.
• the solid solution can still be stored until calcination at 1100 ° C., 10 hours.
• the compositions of the invention have specific reducibility properties.
• the reducibility of the compositions is determined by measuring their capacity to capture hydrogen as a function of temperature.
• a maximum reducibility temperature is also determined by this measurement, which corresponds to the temperature at which the hydrogen uptake is maximum and where, in other words, the reduction of cerium IV to cerium III is also maximum.
• the reducibility of the compositions of the invention can also be measured by their capacity for storing oxygen in dynamic mode (dynamic OSC).
• this dynamic OSC is demonstrated by a test which measures the capacity of the compositions to store oxygen in an oxidizing medium and to restore it in a reducing medium.
• the test evaluates the capacity of the compositions to successively oxidize a certain injected quantity of carbon monoxide of oxygen and to consume a certain injected quantity of oxygen to reoxidize the composition.
• the method used is said to be dynamic because the flows of carbon monoxide and oxygen are alternated at a frequency of 1 Hz (an injection for 1 second).
• the compositions of the invention have an OSC at 400 ° C of at least 0.3 ml of O 2 / g / s.
• This OSC value and all those given in the present description apply to products which have been calcined for 10 hours at 1000 ° C.
• This OSC can be at least 0.4 ml of O 2 / g / s always at 400 ° C.
• This value can be at least 0.9 ml of O 2 / g / s, in particular for compositions whose Ce / Zr ratio is at least 0.5.
• the compositions of the first mode can also have a non-negligible OSC at lower temperature.
• this OSC at 300 ° C. can be at least
• compositions for which the Ce / Zr ratio is at least 0, 5.
• the compositions according to the second mode have an OSC at 400 ° C of at least 0.35 ml of O 2 / g / s.
• this OSC can optionally be at least 1 ml of O 2 / g / s, more particularly at least 1.5 ml of O 2 / g / s and even more particularly at least 2 ml of O 2 / g / s, values of at least about 2.6 ml of O 2 / g / s can be obtained.
• compositions in which the rare earth other than cerium is not the y-trium also have the advantageous characteristic of having a certain OSC at 300 ° C., OSC whose value can be at least 0.2 ml of O 2 / g / s, more particularly at least 0.4 ml of O 2 / g / s.
• the reducibility properties of the compositions of the invention can also result in the presence of at least one reducibility peak at a temperature below 500 ° C. The presence of this peak appears in the curves measuring the quantity of hydrogen captured as a function of the temperature and obtained by the method of measurement of hydrogen capture described above. In the case of the compositions of the invention, these curves show at least one peak at a temperature below 500 ° C.
• this peak also corresponds to a maximum uptake for the curve and is called maximum peak in the present description. More particularly, this peak, whether maximum or not, corresponds to a temperature value below 400 ° C.
• the presence of at least one peak at a temperature below 500 ° C. clearly demonstrates, for the compositions of the invention, that there is a non-negligible reduction activity which begins at a temperature below 500 ° C.
• the compositions of the invention have a specific surface area that is still large even at high calcination temperature, the value of this surface varying according to the embodiment and according to the value of the Ce / Zr ratio. In the case of the first mode and for a Ce / Zr ratio of at least 1, this specific surface after calcination at 1000 ° C., 10 hours, is at least
• this surface is at least 8 m 2 / g, preferably at least 10 m 2 / g and values of at least about 16 m 2 / g can be obtained .
• this specific surface after calcination at 1000 ° C, 10 hours is at least 5 m 2 / g, preferably at least 10 m 2 / g and values of at least about 16 m 2 / g can be obtained.
• this surface is at least 15 m 2 / g, preferably at least 20 m 2 / g and even more preferably at least 30 m 2 / g and values at least about 47 m 2 / g can be obtained.
• this surface can be at least 4 m 2 / g and more particularly at least 10 m 2 / g for the compositions of the second mode in which the rare earth other than cerium is not yttrium.
• the first step of the process therefore consists in preparing a mixture of a zirconium compound, a cerium compound, a tin compound and possibly at least one additional rare earth compound.
• the mixing is generally done in a liquid medium which is preferably water.
• the compounds are preferably soluble compounds. It can in particular be salts of zirconium, cerium, tin and rare earth. These compounds can be chosen in particular from nitrates, sulfates, acetates, chlorides, cerium-ammoniacal nitrates. By way of examples, mention may therefore be made of zirconium sulfate, zirconyl nitrate or zirconyl chloride.
• Zirconyl nitrate is most commonly used. Mention may also be made in particular of the cerium IV salts such as nitrates or cerium-ammoniacal nitrates for example, which are particularly suitable here. Ceric nitrate can be used. It is advantageous to use salts with a purity of at least 99.5% and more particularly of at least 99.9%.
• An aqueous solution of ceric nitrate can for example be obtained by reaction of nitric acid with a hydrated ceric oxide prepared in a conventional manner by reaction of a solution of a cerous salt, for example cerous nitrate, and an ammonia solution in the presence of hydrogen peroxide. It is also possible, in particular, to use a nitrate solution.
• cerium obtained according to the electrolytic oxidation process of a cerous nitrate solution as described in document FR-A-2 570 087, and which here constitutes an advantageous raw material.
• the aqueous solutions of cerium salts and zirconyl salts may have a certain initial free acidity which can be adjusted by the addition of a base or an acid.
• This basic compound can be, for example, an ammonia solution or alternatively alkali hydroxides (sodium, potassium, etc.), but preferably an ammonia solution. It is also possible to use a sol as the starting compound for zirconium or cerium.
• soil any system made up of fine solid particles of colloidal dimensions, that is to say dimensions of between approximately 1 nm and approximately 500 nm, based on a zirconium or cerium compound, this compound generally being an oxide and / or a hydrated oxide of zirconium or of cerium, in suspension in an aqueous liquid phase, said particles possibly also containing, possibly, residual quantities of bound or adsorbed ions such as for example nitrates, acetates, chlorides or ammoniums .
• the zirconium or the cerium can be found either completely in the form of colloids, or simultaneously in the form of ions and in the form of colloids.
• the tin salts such as the halides, the carboxylates in particular the acetates, oxalates, tartrates, ethylhexanoates or acetylacetonates, the sulfates and the organostannic compounds such as the oxides or the chlorides of mono , di or trialkyltin, especially methyl and ethyl.
• Halides are used in particular and especially chloride. Tin chloride is most commonly used in the form of a hydrated salt.
• carboxylates and more particularly oxalates may be preferred insofar as they reduce the risk of pollution by halides.
• the mixture can be indifferently obtained either from compounds initially in the solid state which will then be introduced into a bottom of the water tank for example, or even directly from solutions of these compounds then mixing, in any order, said solutions.
• the mixture obtained in step (a) is brought into contact with a basic compound.
• Products of the hydroxide type can be used as base or basic compound.
• Mention may be made of alkali or alkaline-earth hydroxides. It is also possible to use secondary, tertiary or quaternary amines. However, amines and ammonia may be preferred insofar as they reduce the risks of pollution by alkaline or alkaline earth cations. Mention may also be made of urea.
• the basic compound is generally used in the form of an aqueous solution.
• the manner in which the mixture and the solution are brought into contact, that is to say the order in which they are introduced, is not critical. However, this contacting can be done by introducing the mixture into the solution of the basic compound. This variant is preferable for obtaining the compositions in the form of solid solutions.
• the bringing into contact or the reaction between the mixture and the solution, in particular the addition of the mixture to the solution of the basic compound can be carried out at once, gradually or continuously, and it is preferably carried out with stirring. It is preferably carried out at room temperature.
• the next step in the process is the step of heating the precipitate in an aqueous medium.
• This heating can be carried out directly on the reaction medium obtained after reaction with the basic compound or on a suspension obtained after separation of the precipitate from the reaction medium, optional washing and return to water of the precipitate.
• the temperature to which the medium is heated is at least 100 ° C. and even more particularly at least 130 ° C.
• the heating operation can be carried out by introducing the liquid medium into a closed enclosure (closed reactor of the autoclave type).
• a closed enclosure closed reactor of the autoclave type.
• the pressure in the closed reactor can vary between a value greater than 1 Bar (10 5 Pa) and 165 Bar (1.65. 10 7 Pa), preferably between 5 Bar (5. 10 5 Pa) and 165 Bar (1.65. 10 7 Pa).
• Heating can also be carried out in an open reactor for temperatures close to 100 ° C.
• the heating can be carried out either in air or in an inert gas atmosphere, preferably nitrogen.
• the duration of the heating can vary within wide limits, for example between 1 and 48 hours, preferably between 2 and 24 hours.
• the medium subjected to heating preferably has a basic pH, that is to say that it is greater than 7 and, more particularly, at least 10. It is possible to make several heatings. Thus, the precipitate obtained after the heating step and possibly washing can be resuspended in water and then another heating of the medium thus obtained. This other heating is done under the same conditions as those which were described for the first.
• the product obtained at the end of step (c) can optionally be washed and / or dried, for example by passing through an oven.
• the last step of the process is a calcination step.
• This calcination makes it possible to develop the crystallinity of the product obtained, and it can also be adjusted and / or chosen as a function of the subsequent temperature of use reserved for the composition according to the invention, and this taking into account the fact that the specific surface of the product is lower the higher the calcination temperature used.
• the method of the invention can be implemented according to a variant which will now be described.
• the method according to this variant comprises an additional step, intermediate between the heating step (c) and the calcination step (d). This additional step consists of adding to the precipitate from step
• an additive which is chosen from anionic surfactants, nonionic surfactants, polyethylene glycols and carboxylic acids and their salts and surfactants of the carboxymethylated fatty alcohol ethoxylate type.
• anionic type surfactants ethoxycarboxylates, ethoxylated fatty acids, sarcosinates, esters may be mentioned.
• phosphates such as alcohol sulfates ether alcohol sulfates and sulfated alkanolamide ethoxylates
• sulfonates such as sulfosuccinates, alkyl benzene or alkyl naphthalene sulfonates.
• nonionic surfactant of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, ethylene oxide / propylene oxide copolymers, derivatives sorbiatan, ethylene glycol, propylene glycol, glycerol, polyglyceryl esters and their ethoxylated derivatives, alkylamines, alkylimidazolines, ethoxylated oils and alkylphenol ethoxylates.
• nonionic surfactant of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, ethylene oxide / propylene oxide copolymers, derivatives sorbiatan, ethylene glycol, propylene glycol, glycerol
• carboxylic acids it is possible in particular to use the aliphatic mono- or dicarboxylic acids and, among these, more particularly the saturated acids. It is also possible to use fatty acids and more particularly saturated fatty acids. Mention may thus be made in particular of formic, acetic, propionic, butyric, isobutyric, valeric, caproic, caprylic, capric, lauric, myristic, palmitic acids.
• dicarboxylic acids there may be mentioned oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic acids. Salts of carboxylic acids can also be used.
• a surfactant which is chosen from those of the carboxymethylated fatty alcohol ethoxylate type.
• product of the carboxymethylated fatty alcohol ethoxylate type is meant products consisting of ethoxylated or propoxylated fatty alcohols comprising at the chain end a CH 2 -COOH group.
• a surfactant can consist of a mixture of products of the above formula for which Ri can be saturated and unsaturated respectively or else products comprising both -CH 2 -CH 2 -O groups - and -C (CH 3 ) -CH 2 -O-.
• the addition of the surfactant can be done in two ways. It can be added directly to the precipitate suspension from the previous heating step (c). It can also be added to the solid precipitate after separation from the latter by any known means from the medium in which the heating took place.
• the amount of surfactant used expressed as a percentage by mass of additive relative to the mass of the composition calculated as oxide, is generally between 5% and 100%, more particularly between 15% and 60%.
• compositions of the invention as described above or as obtained by the process mentioned above are in the form of powders but they can optionally be shaped to be in the form of granules, balls, cylinders or nests. bee of variable dimensions.
• These compositions can be applied to any support usually used in the field of catalysis, that is to say in particular thermally inert supports. This support can be chosen from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinels, zeolites, silicates, crystalline silicoaluminum phosphates, phosphates crystalline aluminum.
• compositions can also be used in catalytic systems.
• These catalytic systems can comprise a coating (wash coat) with catalytic properties and based on these compositions, on a substrate of the type, for example metallic or ceramic monolith.
• the coating may also include a support of the type of those mentioned above. This coating is obtained by mixing the composition with the support so as to form a suspension which can then be deposited on the substrate.
• the compositions of the invention can be used in combination with precious metals.
• the nature of these metals and the techniques for incorporating them into these compositions are well known to those skilled in the art.
• the metals can be platinum, rhodium, palladium, gold or iridium, they can in particular be incorporated into the compositions by impregnation.
• the treatment of exhaust gases from internal combustion engines constitutes a particularly interesting application.
• the compositions of the invention can thus be used in this case for three-way catalysis.
• the compositions can be used in combination with a NOx trap (nitrogen oxides) for the treatment of exhaust gases from petrol engines operating in lean mixture (lean bum ) and for example in the three-way catalysis layer of such a trap.
• NOx trap nitrogen oxides
• the compositions of the invention can be incorporated into oxidation catalysts for diesel engines. Therefore, the invention also relates very particularly to a method of treating the exhaust gases of internal combustion engines, which is characterized in that a catalyst composition or system as described above is used as catalyst. .
• Another interesting use is the purification of air at temperatures below 200 ° C or even 100 ° C, this air containing at least one compound of the type carbon monoxide, ethylene, aldehyde, amino, mercaptan, ozone and, d '' in general, of the type of volatile organic compounds or atmospheric pollutants such as fatty acids, hydrocarbons, in particular aromatic hydrocarbons, and nitrogen oxides (for the oxidation of NO to NO 2 ) and of the type smelly compounds. Mention may more particularly be made, as compounds of this kind, of ethanethiol, valeric acid and trimethylamine. This treatment is done by bringing the air to be treated into contact with a composition or a system. catalytic as described above or obtained by the methods detailed above.
• the measurement of the hydrogen capture capacity is made by programmed reduction in temperature as follows.
• a Micromeritics Autochem 2920 device is used with a quartz reactor and a 200 mg sample which has been previously calcined for 10 hours at 1000 ° C. in air.
• the gas is hydrogen at 10% by volume in argon and with a flow rate of 25ml / min.
• the temperature rise is from ambient to 900 ° C at a rate of 20 ° C / min.
• the signal is detected with a thermal conductivity detector.
• the maximum reducibility temperature which has been mentioned above is measured using a thermocouple placed at the heart of the sample.
• the measurement of the OSC-dynamic is made using an Altamira FSR device.
• a first series of examples relates to compositions according to the first embodiment and a second series relates to compositions according to the second mode.
• EXAMPLE 1 This example relates to the preparation of a composition based on cerium, zirconium and tin oxides in the respective proportions by mass of oxide of 21.7%, 73.8% and 4.6%.
• 48 g of cerium nitrate solution in the oxidation state III (496 g / l expressed in oxide) are introduced into a stirred beaker.
• 7 g of tin chloride pentahydrate in the oxidation state IV It is then made up with distilled water so as to obtain 400 ml of a solution of the cerium, zirconium and tin salts.
• EXAMPLE 3 This example relates to the preparation of a composition based on cerium, zirconium and tin oxides in the respective proportions by mass of oxide of 57.8%, 38.1% and 4.1%.
• 120 g of zirconium nitrate solution (270 g / l expressed as oxide), 128 g of cerium nitrate solution in the oxidation state III (496 g / l expressed in oxide) are introduced into a stirred beaker. and 6.2 g of tin chloride pentahydrate in the oxidation state IV. It is then made up with distilled water so as to obtain 400 ml of a solution of the cerium, zirconium and tin salts.
• COMPARATIVE EXAMPLE 4 This example relates to the preparation of a composition based on cerium and zirconium oxides in the respective proportions by mass of oxide of 20% and 80%. 252 g of zirconium nitrate solution (270 g / l expressed as oxide) and 44 g of cerium nitrate solution in the oxidation state III (496 g / l expressed in oxide) are introduced into a stirred beaker It is then made up with distilled water so as to obtain 400 ml of a solution of the cerium, zirconium and tin salts.
• the number (s) in the column “TPR ⁇ 500 ° C” indicates the temperature at which the presence of one or two reducibility peaks is detected during the measurement of the hydrogen capture capacity. The absence of a value in this column means that such a peak was not detected at a temperature below 500 ° C.
• the “TPR max” column indicates the temperature at which the maximum reducibility peak has been detected.
• the “OSC” column gives the value of the oxygen storage capacity measured at 400 ° C. according to the method given above.
• Compositions 2 and 3 have an OSC at 300 ° C of 0.26 and 0.11 ml. g "1. s " 1 respectively.
• EXAMPLE 5 This example relates to the preparation of a composition based on cerium, zirconium, tin and lanthanum oxides in the respective proportions by mass of oxide of 21.4%, 69.4%, 4, 4% and 4.8%.
• 48 g of cerium nitrate solution are introduced into a stirred beaker.
• oxidation state III (496 g / l expressed as oxide), 11 g lanthanum nitrate (450 g / l expressed as oxide) and 6.7 g of tin chloride pentahydrate in the oxidation state IV.
• the precipitate is then resuspended in 600 ml of aqueous solution at pH 10.
• the solution obtained is placed in a stainless steel autoclave equipped with a stirring mobile.
• the temperature of the medium is brought to 150 ° C. for 2 hours with stirring.
• the suspension obtained is filtered by centrifugation and then washed twice with 600 ml of distilled water.
• the product obtained is then dried in an oven at 110 ° C overnight and finally calcined at 500 ° C for 4 hours in level.
• the surfaces obtained after subsequent calcinations at different temperatures are indicated below.
• EXAMPLE 6 This example relates to the preparation of the composition of Example 5 according to the variant of the process using a surfactant. The procedure is carried out in the same manner as in Example 5 until washing in 2 times with 600 ml of distilled water of the precipitate resulting from the filtration by centrifugation of the suspension obtained after the treatment in the autoclave at 150 ° C. 50 g of this precipitate are taken. In parallel, an ammonium laurate gel was prepared under the following conditions: 125 g of lauric acid are introduced into 68 ml of ammonia (12 mol / l) and 250 ml of distilled water, then homogenized with 1 using a spatula.
• EXAMPLE 7 This example relates to the preparation of a composition based on cerium, zirconium, tin and neodymium oxides in the respective proportions by mass of oxide of 21.4%, 69.3%, 4, 4% and 4.9%.
• 47 g of cerium nitrate solution in the oxidation state III (496 g / l expressed in oxide) are introduced into a stirred beaker.
• EXAMPLE 8 This example relates to the preparation of a composition based on cerium, zirconium, tin and yttrium oxides in the respective proportions by mass of oxide of 21.7%, 70.4%, 4 , 5% and 3.4%.
• 48 g of cerium nitrate solution are introduced into a stirred beaker.
• oxidation state III (496 g / l expressed as oxide)
• 150 ml of an ammonia solution are introduced into a stirred reactor
• EXAMPLE 9 This example relates to the preparation of a composition based on cerium, zirconium, tin and lanthanum oxides in the respective proportions by weight of oxide of 41.4%, 50.0%, 4, 1% and 4.5%.
• 92 g of cerium nitrate solution in the oxidation state III (496 g / l expressed in oxide) are introduced into a stirred beaker.
• 11 g of lanthanum nitrate solution 450 g / l expressed as oxide
• 6.2 g of tin chloride pentahydrate in the oxidation state IV 11 g of lanthanum nitrate solution (450 g / l expressed as oxide)
• 6.2 g of tin chloride pentahydrate in the oxidation state IV.
• EXAMPLE 11 This example relates to the preparation of a composition based on cerium, zirconium, tin and lanthanum oxides in the respective proportions by mass of oxide of 69.8%, 22.3%, 3, 8% and 4.1%.
• zirconium nitrate solution (270 g / l expressed as oxide)
• 47 g of cerium nitrate solution in the oxidation state III (496 g / l expressed in oxide) are introduced into an agitated beaker.
• 11 g of lanthanum nitrate solution (450 g / l expressed as oxide)
• 13.4 g of tin chloride pentahydrate in the oxidation state IV. It is then made up with distilled water so as to obtain 400 ml of a solution of the cerium, zirconium, lanthanum and tin salts.
• EXAMPLE 13 This example relates to the preparation of a composition based on cerium, zirconium, tin and praseodymium oxides in the respective proportions by mass of oxide of 21.1%, 69.5%, 4, 3% and 5.1%.
• 76 g of cerium nitrate solution in the oxidation state IV (255 g / l expressed in oxide) are introduced into a stirred beaker.
• EXAMPLE 14 This example relates to the preparation of a composition based on cerium, zirconium, tin and lanthanum oxides in the respective proportions by mass of oxide of 21.5%, 72.6%, 1, 1% and 4.8%. It is a composition with a low tin content. 225 g of zirconium nitrate solution (299 g / l expressed as oxide), 77 g of cerium nitrate solution in the oxidation state IV (255 g / l expressed in oxide) are introduced into a stirred beaker.
• Example 15 This example relates to the preparation of the composition of Example 5 according to a variant of the process using a surfactant and a solution of cerium nitrate with oxidation state IV. 215 g of zirconium nitrate solution (299 g / l expressed as oxide), 77 g of cerium nitrate solution in the oxidation state IV (255 g / I expressed in oxide) are introduced into a stirred beaker.
• the suspension thus obtained is filtered by vacuum filtration and then washed 2 times with 600 ml of distilled water.
• the precipitate is then resuspended in 600 ml of aqueous solution at pH 10.
• the solution obtained is placed in a stainless steel autoclave equipped with a stirring mobile. The temperature of the medium is brought to 150 ° C. for 2 hours with stirring.
• the suspension obtained is filtered by vacuum filtration and then washed 2 times with 600 ml of distilled water. 50 g of the filter cake are taken.
• an ammonium laurate gel was prepared under the following conditions: 125 g of lauric acid are introduced into 68 ml of ammonia (12 mol / l) and 250 ml of distilled water, then homogenized with 1 using a spatula. 15 g of this gel are added to 50 g of the precipitate and the whole is kneaded until a homogeneous paste is obtained. The product obtained is then dried in an oven at 110 ° C overnight and finally calcined at 500 ° C for 4 hours in level. The surfaces obtained after subsequent calcinations at different temperatures are indicated below.
• EXAMPLE 16 This example relates to the preparation of the composition of Example 5 according to a variant of the process using a surfactant and stannous oxalate as tin precursor. 215.5 g of zirconium nitrate solution (299 g / l expressed as oxide), 77 g of cerium nitrate solution in the oxidation state IV (255 g / l expressed in oxide), 11.5 g of lanthanum nitrate (450 g / l expressed as oxide) and 3.9 g of stannous oxalate tin chloride pentahydrate in the oxidation state IV.

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