EP2590737A1 - Composition based on oxides of cerium, of niobium and, optionally, of zirconium and use thereof in catalysis - Google Patents

Composition based on oxides of cerium, of niobium and, optionally, of zirconium and use thereof in catalysis

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Publication number
EP2590737A1
EP2590737A1 EP11731313.0A EP11731313A EP2590737A1 EP 2590737 A1 EP2590737 A1 EP 2590737A1 EP 11731313 A EP11731313 A EP 11731313A EP 2590737 A1 EP2590737 A1 EP 2590737A1
Authority
EP
European Patent Office
Prior art keywords
oxide
composition according
cerium
solution
niobium
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP11731313.0A
Other languages
German (de)
French (fr)
Inventor
Julien Hernandez
Rui Jorge Coelho Marques
Emmanuel Rohart
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rhodia Operations SAS
Original Assignee
Rhodia Operations SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rhodia Operations SAS filed Critical Rhodia Operations SAS
Publication of EP2590737A1 publication Critical patent/EP2590737A1/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • 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
    • 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
    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/20—Vanadium, niobium or tantalum
    • 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
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8625—Nitrogen oxides
    • B01D53/8628—Processes characterised by a specific catalyst
    • 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
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
    • 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
    • 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
    • B01J37/031—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
    • C01F17/30—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C01G25/02—Oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G33/00—Compounds of niobium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G33/00—Compounds of niobium
    • C01G33/006—Compounds containing, besides niobium, two or more other elements, with the exception of oxygen or hydrogen
    • 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
    • B01D2255/20715—Zirconium
    • 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
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • 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
    • C01P2006/12—Surface area
    • 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
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

  • the present invention relates to a composition based on cerium, niobium and optionally zirconium oxides and its use in catalysis, in particular for the treatment of exhaust gases.
  • multifunctional catalysts are used for the treatment of the exhaust gases of internal combustion engines (automotive post-combustion catalysis).
  • multifunctional means catalysts capable of operating not only the oxidation in particular of carbon monoxide and hydrocarbons present in the exhaust gas but also the reduction including nitrogen oxides also present in these gases (catalysts).
  • catalysts capable of operating not only the oxidation in particular of carbon monoxide and hydrocarbons present in the exhaust gas but also the reduction including nitrogen oxides also present in these gases (catalysts).
  • three ways "). Zirconium oxide and ceria appear today as two particularly important and interesting components for this type of catalyst.
  • these catalysts must in particular have good reducibility.
  • Reducibility means, here and for the rest of the description, the ability of the catalyst to reduce in a reducing atmosphere and to reoxidize in an oxidizing atmosphere. This reducibility can be measured for example by a consumption of hydrogen in a given temperature range. It is due to cerium in the case of compositions of the type of those of the invention, the cerium having the property of being reduced or oxidized.
  • these catalysts must have a specific surface that remains sufficient at high temperature.
  • the object of the invention is to provide a composition which has a satisfactory reducibility in combination with good acidity and whose specific surface remains suitable for use in catalysis.
  • composition according to the invention is based on cerium oxide and is characterized in that it comprises niobium oxide with the following proportions by weight:
  • niobium oxide from 2 to 20%
  • rare earth is understood to mean the elements of the group consisting of yttrium and the elements of the Periodic Table with an atomic number inclusive of between 57 and 71.
  • specific surface is meant the specific surface B.E.T. determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in "The Journal of the American Society, 60, 309 (1938)".
  • the calcinations mentioned in the description are calcinations under air unless otherwise indicated.
  • the duration of calcination which is indicated for a temperature corresponds to the duration of the plateau at this temperature.
  • composition of the invention is characterized first of all by the nature and the proportions of its constituents.
  • it is based on cerium and niobium, these elements being present in the composition generally in the form of oxides. These elements are also present in the specific proportions given above.
  • the cerium oxide of the composition can be stabilized, by "stabilized” here means stabilization of the specific surface, by at least one rare earth other than cerium, in oxide form.
  • This rare earth may be more particularly ytthum, neodymium, lanthanum or praseodymium.
  • the stabilizing rare earth oxide content is generally at most 20%, preferably when the rare earth is lanthanum, more preferably at most 15% and preferably at most 10% by weight.
  • the stabilizing rare earth oxide content is not critical but generally it is at least 1%, more particularly at least 2%. This content is expressed as rare earth oxide relative to the mass of the stabilized rare earth cerium oxide-oxide complex.
  • the cerium oxide can also be stabilized, always stabilizing in the sense of the specific surface, by an oxide chosen from silica, alumina and titanium oxide.
  • the content of this stabilizing oxide can be at most 10% and more particularly at most 5%.
  • the minimum content may be at least 1%. This content is expressed as stabilizing oxide relative to the weight of the stabilizing cerium oxide-oxide complex.
  • the composition of the invention comprises three constituent elements, again in the form of oxides, which are cerium, niobium and zirconium.
  • niobium oxide from 2 to 20%
  • the minimum proportion of zirconium oxide in the case of this second embodiment of the invention is preferably at least 10%, more preferably at least 15%.
  • the maximum content of zirconium oxide may more particularly be at most 40% and even more particularly at most 30%.
  • the composition of the invention also contains at least one oxide of an element M chosen from the group comprising tungsten, molybdenum, iron, copper, silicon, aluminum, manganese, titanium, vanadium and rare earths other than cerium, with the following proportions by mass:
  • niobium oxide from 2 to 20%
  • oxide of the element M up to 20%
  • This element M can in particular act as a stabilizer of the surface of the mixed oxide of cerium and zirconium or improve the reducibility of the composition.
  • This element M can in particular act as a stabilizer of the surface of the mixed oxide of cerium and zirconium or improve the reducibility of the composition.
  • the maximum proportion of oxide of element M in the case of rare earths and tungsten may be more particularly at most 15% and even more more particularly at most 10% by weight of oxide of the element M (rare earth and / or tungsten).
  • the minimum content is at least 1%, more particularly at least 2%, the contents given above being expressed relative to the whole oxide of cerium oxide of zirconium oxide of the element M.
  • the oxide content of the element M may more particularly be at most 10% and even more particularly at most 5%.
  • the minimum content may be at least 1%. This content is expressed as the oxide of the element M with respect to the whole cerium oxide-zirconium oxide and oxide of the element M.
  • the element M may be more particularly ryttrium, lanthanum, praseodymium and neodymium.
  • the proportion of niobium oxide may be more particularly between 3% and 15% and even more particularly between 4% and 10%.
  • the cerium content may be at least 65%, more particularly at least 70% and even more particularly at least 75% and that of niobium between 2 and 12% and more particularly between 2 and 10%.
  • the compositions according to this variant have high acidity and reducibility.
  • the proportion of niobium may even more particularly be less than 10% and for example between a minimum value which may be 2% or 4% and a maximum value strictly less than 10%, for example at most 9% and more particularly at most 8% and even more particularly at most 7%.
  • This niobium content is expressed in weight of niobium oxide relative to the mass of the entire composition.
  • compositions of the invention finally have a sufficiently stable surface area, that is to say sufficiently high at high temperature, so that they are used in the field of catalysis.
  • the compositions according to the first embodiment have a specific surface area after calcination for 4 hours at 800 ° C. which is at least 15 m 2 / g, more particularly at least 20 m 2 / g and even more particularly at least 30 m 2 / g.
  • this surface under the same conditions, is generally at least 20 m 2 / g, more particularly at least 30 m 2 / g.
  • the compositions of the invention may have an area of up to about 55 m 2 / g still under the same conditions of calcination.
  • compositions according to the invention in the case where they contain a quantity of niobium of at least 10%, and according to an advantageous embodiment, may have a specific surface after calcination for 4 hours at 800 ° C. which is from minus 35 m 2 / g, more particularly at least 40 m 2 / g.
  • compositions of the invention may have a specific surface after calcination at 900 ° C. for 4 hours which is at least 10 m 2 / g, more particularly at least 15 m 2 / g. Under the same calcination conditions they can have surface areas of up to about 30 m 2 / g.
  • compositions of the invention may have a specific surface after calcination at 1000 ° C. for 4 hours of at least 2 m 2 / g, more particularly at least 3 m 2 / g, and even more particularly at least 4 m 2 / g. Under the same calcination conditions they can have surfaces up to about 10 m 2 / g.
  • compositions of the invention have a high acidity which can be measured by a TPD method, which will be described later, and which is at least 5.10 -2 , more preferably at least 6.10 -2, and more particularly at least 6.4 ⁇ 10 -2, this acidity may especially be at least 7 ⁇ 10 -2 , this acidity being expressed in ml of ammonia per m 2 of product.
  • the area taken into account here is the value expressed in m 2 of the specific surface of the product after calcination at 800 ° C. for 4 hours. Acidities of at least about 9.5 ⁇ 10 -2 can be obtained.
  • compositions of the invention also have significant reducibility properties. These properties can be measured by the programmed temperature reduction measurement method (TPR) which will be described later.
  • the compositions of the invention have a reducibility of at least 15, more particularly at least 20 and even more particularly at least 30. This reducibility is expressed in ml of hydrogen per g of product.
  • the reducibility values given above are for compositions calcined at 800 ° C for 4 hours.
  • the compositions may be in the form of a solid solution of the niobium oxides, the stabilizing element in the case of the first embodiment, zirconium and the element M in the cerium oxide. We then observe in this case the presence of a single phase X-ray diffraction corresponding to the cubic phase of cerium oxide. This characteristic of solid solution generally applies to the compositions which have been calcined at 800 ° C. for 4 hours or at 900 ° C. for 4 hours.
  • the invention also relates to the case where the compositions consist essentially of oxides of the abovementioned elements, cerium, niobium and, where appropriate, zirconium and element M.
  • “Essentially consists of” means that the composition in question contains only the oxides of the elements mentioned above and that it does not contain oxide of another functional element, that is to say likely to have a positive influence on the reducibility and / or the acidity and / or the stability of the composition.
  • the composition may contain elements such as impurities which may notably come from its preparation process, for example raw materials or starting reagents used.
  • compositions of the invention may be prepared by the known method of impregnation.
  • a cerium oxide or a mixed oxide of cerium and zirconium prepared beforehand by a solution comprising a niobium compound, for example an oxalate or an oxalate of niobium and ammonium, is impregnated.
  • a solution which further comprises an oxide of the element M there is used for the impregnation a solution which contains a compound of this element M in addition to the niobium compound.
  • the element M can also be present in the starting cerium oxide which is impregnated.
  • the dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of the impregnant element which is equal to the pore volume of the solid to be impregnated.
  • Cerium oxide or mixed oxide of cerium and zirconium must have specific surface properties which make it suitable for use in catalysis. Thus this surface must be stable, ie it must have a value sufficient for such use even at high temperature.
  • cerium oxides use may be made in particular of those described in patent applications EP 0153227, EP 0388567 and EP 0300852.
  • cerium oxides stabilized by an element such as rare earths, silicon, aluminum and iron it is possible to use use the products described in EP 2160357, EP 547924, EP 588691 and EP 207857.
  • the mixed oxides of cerium and zirconium with optionally an element M especially in the case where M is a rare earth, may be mentioned as suitable products for the present invention those described in patent applications EP 605274, EP 1991354, EP 1660406, EP 1603657, EP 0906244 and EP 0735984.
  • compositions of the invention may also be prepared by a second method which will be described below.
  • This process comprises the following steps:
  • the first step of this process involves a suspension of a niobium hydroxide.
  • This suspension can be obtained by reacting a niobium salt, such as a chloride, with a base, such as ammonia, to obtain a niobium hydroxide precipitate.
  • a niobium salt such as potassium or sodium niobate with an acid such as nitric acid to obtain a niobium hydroxide precipitate.
  • This reaction can be done in a mixture of water and alcohol such as ethanol.
  • the hydroxide thus obtained is washed by any known means and is then resuspended in water in the presence of a peptizing agent such as nitric acid.
  • the second step (b1) of the process comprises mixing the suspension of niobium hydroxide with a solution of a cerium salt.
  • This solution may also contain a zirconium salt and also the element M in the case of the preparation of a composition which further comprises a zirconium oxide or else zirconium oxide and this element M.
  • salts may be chosen from nitrates, sulphates, acetates, chlorides, cerium-ammoniac nitrate.
  • zirconium salts By way of example of zirconium salts, mention may be made of zirconium sulphate, zirconyl nitrate or zirconyl chloride. Zirconyl nitrate is most commonly used. When a cerium salt in form III is used, it is preferable to introduce into the solution of salts an oxidizing agent, for example hydrogen peroxide.
  • an oxidizing agent for example hydrogen peroxide.
  • the different salts of the solution are present in the stoichiometric proportions necessary to obtain the desired final composition.
  • the mixture formed from the niobium hydroxide suspension and the solution of the salts of the other elements is brought into contact with a basic compound.
  • Hydroxide products 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 in that they reduce the risk of pollution by alkaline or alkaline earth cations. We can also mention urea.
  • the basic compound may more particularly be used in the form of a solution.
  • the reaction between the above mixture and the basic compound is preferably continuous in a reactor. This reaction is done by continuously introducing the mixture and the basic compound and continuously withdrawing also the product of the reaction.
  • the precipitate which is obtained is separated from the reaction medium by any conventional solid-liquid separation technique such as, for example, filtration, decantation, spinning or centrifugation.
  • This precipitate can be washed and then calcined at a temperature sufficient to form the oxides, for example at least 500 ° C.
  • compositions of the invention may be further prepared by a third method which comprises the following steps:
  • a mixture in a liquid medium containing a cerium compound and, where appropriate, a zirconium compound and the element M is prepared for the preparation of the compositions which contain zirconium oxide or zirconium oxide and an oxide of the element M;
  • the cerium compound may be a compound of cerium III or cerium IV.
  • the compounds are preferably soluble compounds such as salts. What has been said above for the salts of cerium, zirconium and element M also applies here. It is the same for the nature of the basic compound.
  • the various compounds of the starting mixture of the first step are present in the stoichiometric proportions necessary to obtain the desired final composition.
  • the liquid medium of the first stage is usually water.
  • the starting mixture of the first step can be indifferently obtained either from compounds initially in the solid state which will be introduced later in a water tank for example, or even directly from solutions of these compounds and then mixing, in any order, said solutions.
  • the order of introduction of the reagents into the second step (b2) may be arbitrary, the basic compound may be introduced into the mixture or vice versa or the reagents may be introduced simultaneously into the reactor.
  • the addition can be carried out all at once, gradually or continuously, and it is preferably carried out with stirring.
  • This operation can be conducted at a temperature between room temperature (18-25 ° C) and the reflux temperature of the reaction medium, the latter can reach 120 ° C for example. It is preferably conducted at room temperature.
  • a ripening This can be carried out directly on the reaction medium obtained after contacting with the basic compound or on a suspension obtained after returning the precipitate to water.
  • the ripening is done by heating the environment.
  • the temperature at which the medium is heated is at least 40 ° C, more preferably at least 60 ° C and even more preferably at least 100 ° C.
  • the medium is thus maintained at a constant temperature for a period of time which is usually at least 30 minutes and more particularly at least 1 hour.
  • the ripening can be done at atmospheric pressure or possibly at a higher pressure and a temperature above 100 ° C and in particular between 100 ° C and 150 ° C.
  • the next step (c2) of the process consists in mixing the suspension obtained at the end of the preceding step with a solution of a niobium salt.
  • Niobium salt that may be mentioned niobium chloride, niobate potassium or sodium and especially here niobium oxalate and niobium oxalate and ammonium.
  • This mixture is preferably at room temperature.
  • steps of the process (d2) and (e2) consist in separating the solid from the suspension obtained in the preceding step, optionally washing this solid and then calcining it. These steps proceed in a manner identical to that described above for the second method.
  • the third method may have a variant in which the compound of this element M is not present in step (a2).
  • the compound of the element M is then provided in step (c2) either before or after mixing with the niobium solution or at the same time.
  • the third method can also be implemented according to another variant in which at the end of step (c2) is added to the medium resulting from this step an additive selected from anionic surfactants, nonionic surfactants, polyethylene- glycols, carboxylic acids and their salts and surfactants of the ethoxylates type of carboxymethylated fatty alcohols. Then proceed to step (d2). It is also possible to carry out the steps (c2) and (d2) and then add the aforementioned additive to the solid resulting from the separation.
  • nonionic surfactant may be mentioned more particularly the products sold under the trademark IGEPAL ®, DOWANOL ®, ® and Rhodamox® Alkamide ®.
  • carboxylic acids mention may be made in particular of formic, acetic, propionic, butyric, isobutyric, valeric, caproic, caprylic, capric, lauric, myristic and palmitic acids, as well as their ammoniacal salts.
  • compositions of the invention which are based on the oxides of cerium, niobium and zirconium and optionally an oxide of the element M may also be prepared by a fourth method which will be described below.
  • This process comprises the following steps: - (a3) a mixture in liquid medium containing a zirconium compound and a cerium compound and, where appropriate, the element M;
  • the first step of the process consists in preparing a mixture in a liquid medium of a zirconium compound and a cerium compound and, where appropriate, of the element M.
  • the various compounds of the mixture are present in the necessary stoichiometric proportions to obtain the desired final composition.
  • the liquid medium is usually water.
  • the compounds are preferably soluble compounds. This can be in particular salts of zirconium, cerium and element M as described above.
  • the mixture can be indifferently obtained either from compounds initially in the solid state which will subsequently be introduced into a water tank for example, or even directly from solutions of these compounds and then mixed in any order, of said solutions.
  • the temperature at which this heat treatment, also called thermohydrolysis, is carried out is greater than 100 ° C. It can thus be between 100 ° C. and the critical temperature of the reaction medium, in particular between 100 and 350 ° C., preferably between 100 and 200 ° C.
  • the heating operation can be carried out by introducing the liquid medium into a closed chamber (autoclave-type closed reactor), the necessary pressure then resulting only from the sole heating of the reaction medium (autogenous pressure).
  • autogenous pressure the pressure in the closed reactor can vary between a value greater than 1 bar (10 5 Pa) and 165 bar (1 bar). , 65. 10 7 Pa), preferably between 5 Bar (5 ⁇ 10 5 Pa) and 165 Bar (1, 65. 10 7 Pa). It is of course also possible to exert an external pressure which is added to that subsequent to heating. It is also possible to carry out heating in an open reactor for temperatures close to 100 ° C.
  • the heating may be conducted either in air or in an atmosphere of inert gas, preferably nitrogen.
  • the duration of the treatment is not critical, and can thus vary within wide limits, for example between 1 and 48 hours, preferably between 2 and 24 hours.
  • the rise in temperature is carried out at a speed which is not critical, and it is thus possible to reach the reaction temperature set by heating the medium for example between 30 minutes and 4 hours, these values being given for all purposes. indicative fact.
  • reaction medium thus obtained is brought to a basic pH.
  • This operation is performed by adding to the medium a base such as for example an ammonia solution.
  • basic pH is meant a pH value greater than 7 and preferably greater than 8.
  • the product as recovered can then be subjected to washes, which are then operated with water or optionally with a basic solution, for example an ammonia solution.
  • the washing can be carried out by resuspension in water of the precipitate and maintenance of the suspension thus obtained at a temperature which can go up to 100 ° C.
  • the washed product can optionally be dried, for example in an oven or by atomization, and this at a temperature which can vary between 80 and 300 ° C, preferably between 100 and 200 ° C.
  • the process comprises a ripening (step c'3).
  • the ripening is done under the same conditions as those described above for the third method.
  • the ripening can also be carried out on a suspension obtained after putting the precipitate back into water.
  • the pH of this suspension can be adjusted to a value greater than 7 and preferably greater than 8.
  • the precipitate obtained after the ripening stage can be resuspended in water. optionally washing and then perform another ripening of the medium thus obtained. This other ripening is done under the same conditions as those described for the first. Of course, this operation can be repeated several times.
  • compositions of the invention as described above that is to say the compositions based on cerium, niobium and optionally zirconium oxides and the element are in the form of powders, but they may optionally be used. form to be in the form of granules, balls, cylinders or honeycombs of varying sizes.
  • compositions may be used with any material usually employed in the field of the catalyst system, that is to say in particular a material chosen from thermally inert materials.
  • This material may be chosen from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinels, zeolites, silicates, crystalline silicoaluminium phosphates, phosphates of crystalline aluminum.
  • compositions of the invention still as described above can also be used in catalytic systems comprising a coating (wash coat) with catalytic properties and based on these compositions with a material of the type mentioned above, the coating being deposited on a substrate of the type for example metal monolith, for example FerCralloy, or ceramic, for example cordierite, silicon carbide, alumina titanate or mullite.
  • a coating for example metal monolith, for example FerCralloy, or ceramic, for example cordierite, silicon carbide, alumina titanate or mullite.
  • This coating is obtained by mixing the composition with the material so as to form a suspension which can then be deposited on the substrate.
  • the compositions of the invention may be used in combination with precious metals, they may thus play the role of support for these metals.
  • precious metals they may thus play the role of support for these metals.
  • the nature of these metals and the techniques for incorporating them into the compositions are well known to those skilled in the art.
  • metals can be the platinum, rhodium, palladium, silver, gold or iridium, they can in particular be incorporated into the compositions by impregnation.
  • the catalytic systems and more particularly the compositions of the invention can find very many applications.
  • catalytic systems and more particularly the compositions of the invention can find very many applications. They are thus particularly well adapted to, and therefore usable in, the catalysis of various reactions such as, for example, dehydration, hydrosulfuration, hydrodenitrification, desulfurization, hydrodesulfurization, dehydrohalogenation, reforming, reforming.
  • the systems and compositions of the invention can be used as catalysts in a process involving a gas-to-water reaction, a vapor reforming reaction, an isomerization reaction or a catalytic cracking reaction.
  • the catalyst systems and compositions of the invention can be used as NOx traps.
  • the catalyst systems and compositions of the invention may be more particularly used in the following applications.
  • a first application relates to a process for treating a gas in which a system or a composition of the invention is used as a catalyst for oxidation of CO and hydrocarbons contained in this gas.
  • the systems and compositions of the invention can also be used for the adsorption of NOx, and of CO2 still in the gas treatment.
  • the gas that is treated in these two applications may be a gas from an internal combustion engine (mobile or stationary).
  • compositions of the invention can be used in the formulation of catalysts for three-way catalysis in the treatment of gasoline engine exhaust gases and the catalytic systems of the invention can be used for the implementation of of this catalysis.
  • Another application relates to the use of the systems and compositions of the invention in a process for treating a gas with a view to decomposing N 2 O.
  • N 2 O is found in a large quantity in the gases emitted by certain industrial installations. To avoid N 2 O releases, these gases are treated to decompose N 2 O into oxygen and nitrogen before being released to the atmosphere.
  • the systems and compositions of the invention can be used as catalysts for this decomposition reaction, particularly in a process for preparing nitric acid or adipic acid.
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.0 / 27.0 / 10.0.
  • a suspension of niobium hydroxide is first prepared by the following method.
  • a solution of ammonia D is then prepared by introducing 1040 g of a concentrated ammonia solution (29.8% of NH 3 ) in 6690 g of deionized water.
  • a solution E is prepared by mixing 4250 g of deionized water, 1640 g of a solution of cerium (III) nitrate (30.32% CeO 2 ), 1065 g of a solution of zirconium oxynitrate (20 , 04% ZrO 2 ), 195 g of a solution of hydrogen peroxide (50.30% in H 2 O 2 ), 1935 g of suspension C (4.08% in ⁇ 2 ⁇ ⁇ ). This solution E is stirred.
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 55.1 / 40.0 / 4.9.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 54.0 / 39.1 / 6.9.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by mass: 77.9 / 19.5 / 2.6.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • zirconium oxynitrate solution 770 g
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by mass: 76.6 / 19.2 / 4.2.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 74.2 / 18.6 / 7.2.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • zirconium oxynitrate solution 770 g
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by mass: 72.1 / 18.0 / 9.9.
  • a solution of niobium oxalate (V) and ammonium is prepared by hot dissolving 192 g of niobium (V) oxalate and ammonium in 300 g of deionized water.
  • This solution is maintained at 50 ° C.
  • the concentration of this solution is 14.2% Nb 2 O 5 .
  • This solution is then introduced onto a powder of a mixed oxide of cerium and zirconium (mass composition CeO 2 / ZrO 2 80/20, specific surface after calcination at 800 ° C. 4 hours of 59 m 2 / g) to saturation of the pore volume.
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 68.7 / 17.2 / 14.1.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide and niobium oxide in the respective proportions by mass: 96.8 / 3.2.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but without zirconium oxynitrate and in the following proportions:
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide and niobium oxide in the following respective proportions by weight: 91.4% / 8.6%.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but without zirconium oxynitrate and in the following proportions:
  • This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.0 / 27.0 / 10.0.
  • a solution of zirconium nitrates and cerium IV is prepared by mixing 264 g of deionized water, 238 g of cerium (IV) nitrate solution (252 g / L in CeO 2 ) and 97 grams of sodium hydroxide solution. zirconium oxynitrate (261 g / l in ZrO 2 ). The concentration of this solution is 120 g / l of oxide.
  • the nitrate solution is introduced in one hour.
  • the final pH is around 9.5.
  • the suspension thus prepared is cured at 95 ° C. for 2 hours. The medium is then allowed to cool.
  • a solution of niobium oxalate (V) is prepared by hot dissolving 44.8 g of niobium oxalate (V) in 130 g of deionized water.
  • This solution is maintained at 50 ° C.
  • the concentration of this solution is 3.82% in Nb 2 O 5 .
  • the suspension is filtered and washed.
  • the cake is then introduced into an oven and calcined at 800.degree.
  • This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight 63.3 / 26.7 / 10.0.
  • a solution of nitrates of zirconium and cerium IV is prepared by mixing 451 g of deionized water, 206 g of cerium (IV) nitrate solution (252 g / l of CeO 2 ) and 75 g of sodium nitrate solution. zirconium oxynitrate (288 g / l ZrO 2 ). The concentration of this solution is 80 g / l of oxide.
  • the temperature is raised to 100 ° C.
  • the medium is stirred at 100 ° C. for 1 hour.
  • the suspension is transferred to a stirred reactor of 1.5 liters.
  • the suspension is cured at 95 ° C for 2 hours.
  • the medium is then allowed to cool.
  • a solution of niobium oxalate (V) is prepared by hot dissolving 39 g of niobium oxalate (V) in 13 g of deionized water.
  • This solution is maintained at 50 ° C.
  • the concentration of this solution is 3.84% in Nb 2 O 5 .
  • the pH is then raised to pH 9 by adding an ammonia solution (32% NH 3 ).
  • the suspension is filtered and washed.
  • the cake is then introduced into an oven and calcined at 800 ° C. (4 hour stage).
  • This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 64.0 / 27.0 / 9.0.
  • niobium oxalate (V) is prepared by hot dissolving 35.1 g of niobium oxalate (V) in 13 g of deionized water. The concentration of this solution is 3.45% Nb 2 O 5.
  • This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 19.4 / 77.6 / 3.0.
  • a solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
  • a solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
  • the acidity properties are measured by the TPD method which is described below.
  • the probe molecule used to characterize acid sites in TPD is ammonia.
  • the sample is heated to 500 ° C. under a stream of helium (30 ml / min) according to a rise in temperature of 20 ° C./min and is maintained at this temperature for 30 minutes in order to remove the water vapor and avoid puncturing the pores. Finally the sample is cooled to 100 ° C under a stream of helium at 10 ° C / min.
  • the sample is then subjected to a flux (30 ml / min) of ammonia (5% vol of NH 3 in helium at 100 ° C) at atmospheric pressure for 30 minutes (until saturation).
  • the sample is subjected for a minimum of 1 hour to a stream of helium.
  • TPD is conducted by raising the temperature by 10 ° C / min to 700 ° C.
  • the concentration of the desorbed species that is to say ammonia
  • TCD thermal conductivity detector
  • the reducibility properties are measured by performing a programmed temperature reduction (TPR) on a Micromeritics Autochem 2. This meter measures the hydrogen consumption of a composition as a function of temperature.
  • TPR programmed temperature reduction
  • hydrogen is used as a reducing gas at 10% by volume in argon with a flow rate of 30 ml / min.
  • the experimental protocol consists in weighing 200 mg of the sample in a previously tared container.
  • the sample is then introduced into a quartz cell containing in the bottom of the quartz wool.
  • the sample is finally covered with quartz wool and positioned in the oven of the measuring device.
  • the temperature program is as follows:
  • the temperature of the sample is measured using a thermocouple placed in the quartz cell above the sample.
  • Hydrogen consumption during the reduction phase is deduced by calibrating the variation of the thermal conductivity of the gas stream measured at the outlet of the cell using a thermal conductivity detector (TCD).
  • TCD thermal conductivity detector
  • the hydrogen consumption is measured between 30 ° C and 900 ° C.
  • compositions according to the invention have both good properties of reducibility and acidity.
  • the composition of the comparative example has good acidity properties but the reducibility properties are much lower than those of the compositions of the invention.

Abstract

The invention relates to a composition based on cerium oxide and on niobium oxide in a proportion of niobium oxide from 2 to 20%. This composition may additionally comprise zirconium oxide. In this case, the proportions are at least 50% of cerium oxide, between 2 and 20% of niobium oxide and at most 48% of zirconium oxide. The composition of the invention may be used in particular for treating exhaust gases.

Description

COMPOSITION A BASE D'OXYDES DE CERIUM, DE NIOBIUM ET, EVENTUELLEMENT, DE ZIRCONIUM ET SON UTILISATION EN CATALYSE  COMPOSITION BASED ON OXIDES OF CERIUM, NIOBIUM AND, POSSIBLY, ZIRCONIUM AND USE THEREOF IN CATALYSIS
La présente invention concerne une composition à base d'oxydes de cérium, de niobium et, éventuellement de zirconium et son utilisation en catalyse, notamment pour le traitement des gaz d'échappement. The present invention relates to a composition based on cerium, niobium and optionally zirconium oxides and its use in catalysis, in particular for the treatment of exhaust gases.
On utilise à l'heure actuelle pour le traitement des gaz d'échappement des moteurs à combustion interne (catalyse postcombustion automobile) des catalyseurs dits multifonctionnels. Par multifonctionnels, on entend les catalyseurs capables d'opérer non seulement l'oxydation en particulier du monoxyde de carbone et des hydrocarbures présents dans les gaz d'échappement mais également la réduction notamment des oxydes d'azote également présents dans ces gaz (catalyseurs "trois voies"). L'oxyde de zirconium et l'oxyde de cérium apparaissent aujourd'hui comme deux constituants particulièrement importants et intéressants pour ce type de catalyseurs.  At the present time, so-called multifunctional catalysts are used for the treatment of the exhaust gases of internal combustion engines (automotive post-combustion catalysis). By multifunctional means catalysts capable of operating not only the oxidation in particular of carbon monoxide and hydrocarbons present in the exhaust gas but also the reduction including nitrogen oxides also present in these gases (catalysts). three ways "). Zirconium oxide and ceria appear today as two particularly important and interesting components for this type of catalyst.
Pour être efficaces, ces catalyseurs doivent présenter notamment une bonne réductibilité. On entend par réductibilité, ici et pour le reste de la description, la capacité du catalyseur à se réduire en atmosphère réductrice et à se réoxyder en atmosphère oxydante. Cette réductibilité peut se mesurer par exemple par une consommation d'hydrogène dans un domaine de température donné. Elle est due au cérium dans le cas des compositions du type de celles de l'invention, le cérium ayant la propriété de se réduire ou de s'oxyder.  To be effective, these catalysts must in particular have good reducibility. Reducibility means, here and for the rest of the description, the ability of the catalyst to reduce in a reducing atmosphere and to reoxidize in an oxidizing atmosphere. This reducibility can be measured for example by a consumption of hydrogen in a given temperature range. It is due to cerium in the case of compositions of the type of those of the invention, the cerium having the property of being reduced or oxidized.
Par ailleurs, ces produits doivent présenter une acidité suffisante permettant par exemple une meilleure résistance à la sulfatation.  Moreover, these products must have sufficient acidity allowing for example a better resistance to sulfation.
Enfin, pour être efficaces, ces catalyseurs doivent présenter une surface spécifique qui reste suffisante à température élevée.  Finally, to be effective, these catalysts must have a specific surface that remains sufficient at high temperature.
L'objet de l'invention est de fournir une composition qui présente une réductibilité satisfaisante en combinaison avec une bonne acidité et dont la surface spécifique reste adaptée à un emploi en catalyse.  The object of the invention is to provide a composition which has a satisfactory reducibility in combination with good acidity and whose specific surface remains suitable for use in catalysis.
Dans ce but, la composition selon l'invention est à base d'oxyde de cérium et elle est caractérisée en ce qu'elle comprend de l'oxyde de niobium avec les proportions suivantes en masse :  For this purpose, the composition according to the invention is based on cerium oxide and is characterized in that it comprises niobium oxide with the following proportions by weight:
- oxyde de niobium : de 2 à 20%;  niobium oxide: from 2 to 20%;
le complément en oxyde de cérium. D'autres caractéristiques, détails et avantages de l'invention apparaîtront encore plus complètement à la lecture de la description qui va suivre, ainsi que des divers exemples concrets mais non limitatifs destinés à l'illustrer. the complement in cerium oxide. Other features, details and advantages of the invention will appear even more fully on reading the description which follows, as well as various concrete but non-limiting examples intended to illustrate it.
Pour la présente description on entend par terre rare les éléments du groupe constitué par l'yttrium et les éléments de la classification périodique de numéro atomique compris inclusivement entre 57 et 71 .  For the purposes of this description rare earth is understood to mean the elements of the group consisting of yttrium and the elements of the Periodic Table with an atomic number inclusive of between 57 and 71.
On entend par surface spécifique, la surface spécifique B.E.T. déterminée par adsorption d'azote conformément à la norme ASTM D 3663-78 établie à partir de la méthode BRUNAUER - EMMETT- TELLER décrite dans le périodique "The Journal of the American Society, 60, 309 (1938)".  By specific surface is meant the specific surface B.E.T. determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in "The Journal of the American Society, 60, 309 (1938)".
Les valeurs de surface spécifiques qui sont indiquées pour une température et une durée données correspondent, sauf indication contraire, à des calcinations sous air à un palier à cette température et sur la durée indiquée.  The specific surface values that are given for a given temperature and time, unless otherwise indicated, correspond to single stage air calcinations at that temperature and over the specified time.
Les calcinations mentionnées dans la description sont des calcinations sous air sauf indication contraire. La durée de calcination qui est indiquée pour une température correspond à la durée du palier à cette température.  The calcinations mentioned in the description are calcinations under air unless otherwise indicated. The duration of calcination which is indicated for a temperature corresponds to the duration of the plateau at this temperature.
Les teneurs ou proportions sont données en masse et en oxyde (notamment CeO2, Ln2O3, Ln désignant une terre rare trivalente, Pr6On dans le cas particulier du praséodyme, Nb^Os dans le cas du niobium) sauf indication contraire. The contents or proportions are given in mass and in oxide (in particular CeO 2 , Ln 2 O 3, Ln denoting a trivalent rare earth, Pr 6 In the particular case of praseodymium, Nb ^ Os in the case of niobium) unless otherwise indicated.
On précise aussi pour la suite de la description que, sauf indication contraire, dans les fourchettes de valeurs qui sont données, les valeurs aux bornes sont incluses.  It is also specified for the remainder of the description that, unless otherwise indicated, in the ranges of values that are given, the values at the terminals are included.
La composition de l'invention se caractérise tout d'abord par la nature et les proportions de ses constituants. Ainsi, et selon un premier mode de réalisation, elle est à base de cérium et de niobium, ces éléments étant présents dans la composition généralement sous la forme d'oxydes. Ces éléments sont par ailleurs présents dans les proportions spécifiques qui ont été données plus haut.  The composition of the invention is characterized first of all by the nature and the proportions of its constituents. Thus, and according to a first embodiment, it is based on cerium and niobium, these elements being present in the composition generally in the form of oxides. These elements are also present in the specific proportions given above.
L'oxyde de cérium de la composition peut être stabilisé, par « stabilisé » on entend ici stabilisation de la surface spécifique, par au moins une terre rare autre que le cérium, sous forme oxyde. Cette terre rare peut être plus particulièrement l'ytthum, le néodyme, le lanthane ou le praséodyme. La teneur en oxyde de terre rare stabilisant est généralement d'au plus 20%, de préférence lorsque la terre rare est le lanthane, plus particulièrement d'au plus 15% et de préférence d'au plus 10% en masse. La teneur en oxyde de terre rare stabilisant n'est pas critique mais généralement elle est d'au moins 1 %, plus particulièrement d'au moins 2%. Cette teneur est exprimée en oxyde de la terre rare par rapport à la masse de l'ensemble oxyde de cérium-oxyde de terre rare stabilisant. The cerium oxide of the composition can be stabilized, by "stabilized" here means stabilization of the specific surface, by at least one rare earth other than cerium, in oxide form. This rare earth may be more particularly ytthum, neodymium, lanthanum or praseodymium. The stabilizing rare earth oxide content is generally at most 20%, preferably when the rare earth is lanthanum, more preferably at most 15% and preferably at most 10% by weight. The stabilizing rare earth oxide content is not critical but generally it is at least 1%, more particularly at least 2%. This content is expressed as rare earth oxide relative to the mass of the stabilized rare earth cerium oxide-oxide complex.
L'oxyde de cérium peut être stabilisé aussi, stabilisation toujours au sens de la surface spécifique, par un oxyde choisi parmi la silice, l'alumine et l'oxyde de titane. La teneur en cet oxyde stabilisant peut être d'au plus 10% et plus particulièrement d'au plus 5%. La teneur minimale peut être d'au moins 1 %. Cette teneur est exprimée en oxyde de stabilisant par rapport à la masse de l'ensemble oxyde de cérium-oxyde stabilisant.  The cerium oxide can also be stabilized, always stabilizing in the sense of the specific surface, by an oxide chosen from silica, alumina and titanium oxide. The content of this stabilizing oxide can be at most 10% and more particularly at most 5%. The minimum content may be at least 1%. This content is expressed as stabilizing oxide relative to the weight of the stabilizing cerium oxide-oxide complex.
Selon un autre mode de réalisation de l'invention, la composition de l'invention comprend trois éléments constitutifs, là aussi sous forme d'oxydes, qui sont le cérium, le niobium et le zirconium.  According to another embodiment of the invention, the composition of the invention comprises three constituent elements, again in the form of oxides, which are cerium, niobium and zirconium.
Les proportions respectives de ces éléments sont alors les suivantes : The respective proportions of these elements are then as follows:
- oxyde de cérium : au moins 50%; - cerium oxide: at least 50%;
- oxyde de niobium : de 2 à 20%;  niobium oxide: from 2 to 20%;
- oxyde de zirconium : jusqu'à 48%.  - zirconium oxide: up to 48%.
La proportion minimale en oxyde de zirconium dans le cas de ce second mode de réalisation de l'invention est de préférence d'au moins 10%, plus particulièrement d'au moins 15%. La teneur maximale en oxyde de zirconium peut être plus particulièrement d'au plus 40% et encore plus particulièrement d'au plus 30%.  The minimum proportion of zirconium oxide in the case of this second embodiment of the invention is preferably at least 10%, more preferably at least 15%. The maximum content of zirconium oxide may more particularly be at most 40% and even more particularly at most 30%.
Selon un troisième mode de réalisation de l'invention la composition de l'invention contient en outre au moins un oxyde d'un élément M choisi dans le groupe comprenant le tungstène, le molybdène, le fer, le cuivre, le silicium, l'aluminium, le manganèse, le titane, le vanadium et les terres rares autres que le cérium, avec les proportions suivantes en masse :  According to a third embodiment of the invention, the composition of the invention also contains at least one oxide of an element M chosen from the group comprising tungsten, molybdenum, iron, copper, silicon, aluminum, manganese, titanium, vanadium and rare earths other than cerium, with the following proportions by mass:
- oxyde de cérium : au moins 50%;  - cerium oxide: at least 50%;
- oxyde de niobium : de 2 à 20%;  niobium oxide: from 2 to 20%;
- oxyde de l'élément M : jusqu'à 20%;  oxide of the element M: up to 20%;
- le complément en oxyde de zirconium.  the zirconium oxide supplement.
Cet élément M peut notamment jouer le rôle de stabilisant de la surface de l'oxyde mixte de cérium et de zirconium ou encore améliorer la réductibilité de la composition. Pour la suite de la description on doit comprendre que, si par souci de simplification on ne mentionne qu'un élément M, il est bien entendu que l'invention s'applique au cas où les compositions comprennent plusieurs éléments M.  This element M can in particular act as a stabilizer of the surface of the mixed oxide of cerium and zirconium or improve the reducibility of the composition. For the remainder of the description, it should be understood that, if, for the sake of simplicity, only one element M is mentioned, it is understood that the invention applies to the case where the compositions comprise several elements M.
La proportion maximale en oxyde de l'élément M dans le cas des terres rares et du tungstène peut être plus particulièrement d'au plus 15% et encore plus particulièrement d'au plus 10% en masse d'oxyde de l'élément M (terre rare et/ou tungstène). La teneur minimale est d'au moins 1 %, plus particulièrement d'au moins 2%, les teneurs données ci-dessus étant exprimées par rapport à l'ensemble oxyde de cérium-oxyde de zirconium- oxyde de l'élément M. The maximum proportion of oxide of element M in the case of rare earths and tungsten may be more particularly at most 15% and even more more particularly at most 10% by weight of oxide of the element M (rare earth and / or tungsten). The minimum content is at least 1%, more particularly at least 2%, the contents given above being expressed relative to the whole oxide of cerium oxide of zirconium oxide of the element M.
Dans le cas où M n'est ni une terre rare ni le tungstène, la teneur en l'oxyde de l'élément M peut être plus particulièrement d'au plus 10% et encore plus particulièrement d'au plus 5%. La teneur minimale peut être d'au moins 1 %. Cette teneur est exprimée en oxyde de l'élément M par rapport à l'ensemble oxyde de cérium-oxyde de zirconium et oxyde de l'élément M.  In the case where M is neither a rare earth nor tungsten, the oxide content of the element M may more particularly be at most 10% and even more particularly at most 5%. The minimum content may be at least 1%. This content is expressed as the oxide of the element M with respect to the whole cerium oxide-zirconium oxide and oxide of the element M.
Dans le cas des terres rares, l'élément M peut être plus particulièrement ryttrium, le lanthane, le praséodyme et le néodyme.  In the case of rare earths, the element M may be more particularly ryttrium, lanthanum, praseodymium and neodymium.
Pour les différents modes de réalisation décrits ci-dessus, la proportion en oxyde de niobium peut être comprise plus particulièrement entre 3% et 15% et encore plus particulièrement entre 4% et 10%.  For the various embodiments described above, the proportion of niobium oxide may be more particularly between 3% and 15% and even more particularly between 4% and 10%.
Dans le cas des compositions selon le second ou le troisième mode et selon une variante avantageuse, la teneur en cérium peut être d'au moins 65%, plus particulièrement d'au moins 70% et encore plus particulièrement d'au moins 75% et celle en niobium comprise entre 2 et 12% et plus particulièrement entre 2 et 10%. Les compositions selon cette variante présentent une acidité et une réductibilité élevées.  In the case of the compositions according to the second or third mode and according to an advantageous variant, the cerium content may be at least 65%, more particularly at least 70% and even more particularly at least 75% and that of niobium between 2 and 12% and more particularly between 2 and 10%. The compositions according to this variant have high acidity and reducibility.
Toujours pour ces différents modes de réalisation la proportion en niobium peut être encore plus particulièrement inférieure à 10% et par exemple comprise entre une valeur minimale qui peut être de 2% ou de 4% et une valeur maximale strictement inférieure à 10% par exemple d'au plus 9% et plus particulièrement d'au plus 8% et encore plus particulièrement d'au plus 7%. Cette teneur en niobium est exprimée en masse d'oxyde de niobium par rapport à la masse de l'ensemble de la composition. Les valeurs pour les proportions en niobium qui viennent d'être données, notamment celle strictement inférieure à 10% s'appliquent à la variante avantageuse selon le second ou le troisième mode qui a été décrit précédemment.  For these different embodiments, the proportion of niobium may even more particularly be less than 10% and for example between a minimum value which may be 2% or 4% and a maximum value strictly less than 10%, for example at most 9% and more particularly at most 8% and even more particularly at most 7%. This niobium content is expressed in weight of niobium oxide relative to the mass of the entire composition. The values for the proportions of niobium which have just been given, especially that strictly less than 10%, apply to the advantageous variant according to the second or the third mode which has been described previously.
Les compositions de l'invention présentent enfin une surface spécifique suffisamment stable, c'est-à-dire suffisamment élevée à haute température, pour qu'elles soient utilisables dans le domaine de la catalyse.  The compositions of the invention finally have a sufficiently stable surface area, that is to say sufficiently high at high temperature, so that they are used in the field of catalysis.
Ainsi, généralement, les compositions selon le premier mode présentent une surface spécifique après calcination 4 heures à 800°C qui est d'au moins 15 m2/g, plus particulièrement d'au moins 20 m2/g et encore plus particulièrement d'au moins 30 m2/g. Pour les compositions selon le second et le troisième mode de réalisation cette surface, dans les mêmes conditions, est généralement d'au moins 20 m2/g, plus particulièrement d'au moins 30 m2/g. Pour les trois modes, les compositions de l'invention peuvent présenter une surface allant jusqu'à environ 55 m2/g toujours dans les mêmes conditions de calcination. Thus, generally, the compositions according to the first embodiment have a specific surface area after calcination for 4 hours at 800 ° C. which is at least 15 m 2 / g, more particularly at least 20 m 2 / g and even more particularly at least 30 m 2 / g. For compositions according to the second and the third embodiment this surface, under the same conditions, is generally at least 20 m 2 / g, more particularly at least 30 m 2 / g. For the three modes, the compositions of the invention may have an area of up to about 55 m 2 / g still under the same conditions of calcination.
Les compositions selon l'invention, dans le cas où elles contiennent une quantité de niobium d'au moins 10%, et selon un mode de réalisation avantageux, peuvent présenter une surface spécifique après calcination 4 heures à 800°C qui est d'au moins 35 m2/g, plus particulièrement d'au moins 40 m2/g. The compositions according to the invention, in the case where they contain a quantity of niobium of at least 10%, and according to an advantageous embodiment, may have a specific surface after calcination for 4 hours at 800 ° C. which is from minus 35 m 2 / g, more particularly at least 40 m 2 / g.
Toujours pour les trois modes, les compositions de l'invention peuvent présenter une surface spécifique après calcination à 900°C 4 heures qui est d'au moins 10 m2/g, plus particulièrement d'au moins 15 m2/g. Dans les mêmes conditions de calcination elles peuvent avoir des surfaces surface allant jusqu'à environ 30 m2/g. Still for the three modes, the compositions of the invention may have a specific surface after calcination at 900 ° C. for 4 hours which is at least 10 m 2 / g, more particularly at least 15 m 2 / g. Under the same calcination conditions they can have surface areas of up to about 30 m 2 / g.
Les compositions de l'invention, pour les trois modes, peuvent présenter une surface spécifique après calcination à 1000°C 4 heures d'au moins 2 m2/g, plus particulièrement d'au moins 3 m2/g et encore plus particulièrement d'au moins 4 m2/g. Dans les mêmes conditions de calcination elles peuvent avoir des surfaces allant jusqu'à environ 10 m2/g. The compositions of the invention, for the three modes, may have a specific surface after calcination at 1000 ° C. for 4 hours of at least 2 m 2 / g, more particularly at least 3 m 2 / g, and even more particularly at least 4 m 2 / g. Under the same calcination conditions they can have surfaces up to about 10 m 2 / g.
Les compositions de l'invention présentent une acidité élevée qui peut être mesurée par une méthode d'analyse TPD, qui sera décrite plus loin, et qui est d'au moins 5.10"2, plus particulièrement d'au moins 6.10"2 et encore plus particulièrement d'au moins 6,4.10"2. Cette acidité peut être notamment d'au moins 7.10"2, cette acidité étant exprimée en ml d'ammoniac par m2 de produit. La surface prise en compte ici est la valeur exprimée en m2 de la surface spécifique du produit après calcination à 800°C 4 heures. Des acidités d'au moins environ 9,5.10"2 peuvent être obtenues. The compositions of the invention have a high acidity which can be measured by a TPD method, which will be described later, and which is at least 5.10 -2 , more preferably at least 6.10 -2, and more particularly at least 6.4 × 10 -2, this acidity may especially be at least 7 × 10 -2 , this acidity being expressed in ml of ammonia per m 2 of product. The area taken into account here is the value expressed in m 2 of the specific surface of the product after calcination at 800 ° C. for 4 hours. Acidities of at least about 9.5 × 10 -2 can be obtained.
Les compositions de l'invention présentent aussi des propriétés de réductibilité importantes. Ces propriétés peuvent être mesurées par la méthode de mesure de réduction en température programmée (TPR) qui sera décrite plus loin. Les compositions de l'invention présentent une réductibilité d'au moins 15, plus particulièrement d'au moins 20 et encore plus particulièrement d'au moins 30. Cette réductibilité est exprimée en ml d'hydrogène par g de produit. Les valeurs de réductibilité données ci- dessus le sont pour des compositions ayant subi une calcination à 800°C pendant 4 heures. Les compositions peuvent se présenter sous la forme d'une solution solide des oxydes du niobium, de l'élément stabilisant dans le cas du premier mode de réalisation, du zirconium et de l'élément M dans l'oxyde de cérium. On observe alors dans ce cas la présence d'une phase unique en diffraction des rayons X correspondant à la phase cubique de l'oxyde de cérium. Cette caractéristique de solution solide s'applique généralement aux compositions ayant subi une calcination à 800°C 4 heures ou encore à 900°C 4 heures. The compositions of the invention also have significant reducibility properties. These properties can be measured by the programmed temperature reduction measurement method (TPR) which will be described later. The compositions of the invention have a reducibility of at least 15, more particularly at least 20 and even more particularly at least 30. This reducibility is expressed in ml of hydrogen per g of product. The reducibility values given above are for compositions calcined at 800 ° C for 4 hours. The compositions may be in the form of a solid solution of the niobium oxides, the stabilizing element in the case of the first embodiment, zirconium and the element M in the cerium oxide. We then observe in this case the presence of a single phase X-ray diffraction corresponding to the cubic phase of cerium oxide. This characteristic of solid solution generally applies to the compositions which have been calcined at 800 ° C. for 4 hours or at 900 ° C. for 4 hours.
L'invention concerne aussi le cas où les compositions consistent essentiellement en oxydes des éléments précités, cérium, niobium et, le cas échéant zirconium et élément M. Par « consiste essentiellement », on entend que la composition considérée ne contient que les oxydes des éléments précités et qu'il ne contient pas d'oxyde d'un autre élément fonctionnel, c'est à dire susceptible d'avoir une influence positive sur la réductibilité et/ou l'acidité et/ou la stabilité de la composition. Par contre, la composition peut contenir des éléments tels que des impuretés pouvant notamment provenir de son procédé de préparation, par exemple des matières premières ou des réactifs de départ utilisés.  The invention also relates to the case where the compositions consist essentially of oxides of the abovementioned elements, cerium, niobium and, where appropriate, zirconium and element M. "Essentially consists of" means that the composition in question contains only the oxides of the elements mentioned above and that it does not contain oxide of another functional element, that is to say likely to have a positive influence on the reducibility and / or the acidity and / or the stability of the composition. On the other hand, the composition may contain elements such as impurities which may notably come from its preparation process, for example raw materials or starting reagents used.
Les compositions de l'invention peuvent être préparées par le procédé connu d'imprégnation. Ainsi, on imprègne un oxyde de cérium ou un oxyde mixte de cérium et de zirconium préalablement préparé par une solution comprenant un composé de niobium par exemple un oxalate ou un oxalate de niobium et d'ammonium. Dans le cas de la préparation d'une composition qui comprend en outre un oxyde de l'élément M on utilise pour l'imprégnation une solution qui contient un composé de cet élément M en plus du composé de niobium. L'élément M peut aussi être présent dans l'oxyde de cérium de départ que l'on imprègne.  The compositions of the invention may be prepared by the known method of impregnation. Thus, a cerium oxide or a mixed oxide of cerium and zirconium prepared beforehand by a solution comprising a niobium compound, for example an oxalate or an oxalate of niobium and ammonium, is impregnated. In the case of the preparation of a composition which further comprises an oxide of the element M, there is used for the impregnation a solution which contains a compound of this element M in addition to the niobium compound. The element M can also be present in the starting cerium oxide which is impregnated.
On utilise plus particulièrement l'imprégnation à sec. L'imprégnation à sec consiste à ajouter au produit à imprégner un volume d'une solution aqueuse de l'élément imprégnant qui est égal au volume poreux du solide à imprégner.  It is more particularly used dry impregnation. The dry impregnation consists in adding to the product to be impregnated a volume of an aqueous solution of the impregnant element which is equal to the pore volume of the solid to be impregnated.
L'oxyde de cérium ou l'oxyde mixte de cérium et de zirconium doit présenter des propriétés de surface spécifique qui le rendent apte à une utilisation en catalyse. Ainsi cette surface doit être stable, c'est à dire qu'elle doit présenter une valeur suffisante pour une telle utilisation même à température élevée.  Cerium oxide or mixed oxide of cerium and zirconium must have specific surface properties which make it suitable for use in catalysis. Thus this surface must be stable, ie it must have a value sufficient for such use even at high temperature.
De tels oxydes sont bien connus. Pour les oxydes de cérium on peut utiliser notamment ceux décrits dans les demandes de brevet EP 0153227, EP 0388567 et EP 0300852. Pour les oxydes de cérium stabilisés par un élément comme les terres rares, le silicium, l'aluminium et le fer on peut utiliser les produits décrits dans EP 2160357, EP 547924, EP 588691 et EP 207857. Pour les oxydes mixtes de cérium et de zirconium avec éventuellement un élément M, notamment dans le cas où M est une terre rare, on peut mentionner comme produits qui conviennent pour la présente invention ceux décrits dans les demandes de brevet EP 605274, EP 1991354, EP 1660406, EP 1603657, EP 0906244 et EP 0735984. Pour la mise en œuvre de la présente invention, on pourra donc, si nécessaire, se référer à l'ensemble de la description des demandes de brevet mentionnées ci-dessus. Such oxides are well known. For the cerium oxides, use may be made in particular of those described in patent applications EP 0153227, EP 0388567 and EP 0300852. For cerium oxides stabilized by an element such as rare earths, silicon, aluminum and iron, it is possible to use use the products described in EP 2160357, EP 547924, EP 588691 and EP 207857. For the mixed oxides of cerium and zirconium with optionally an element M, especially in the case where M is a rare earth, may be mentioned as suitable products for the the present invention those described in patent applications EP 605274, EP 1991354, EP 1660406, EP 1603657, EP 0906244 and EP 0735984. For the implementation of the present invention, it will therefore be possible, if necessary, to refer to the set of the description of the patent applications mentioned above.
Les compositions de l'invention peuvent être préparées aussi par un second procédé qui va être décrit ci-dessous.  The compositions of the invention may also be prepared by a second method which will be described below.
Ce procédé comprend les étapes suivantes :  This process comprises the following steps:
- (a1 ) on mélange une suspension d'un hydroxyde de niobium avec une solution comprenant des sels de cérium et, le cas échéant de zirconium et de l'élément M;  (a1) mixing a suspension of a niobium hydroxide with a solution comprising cerium salts and, if appropriate zirconium and element M;
- (b1 ) on met en présence le mélange ainsi formé avec un composé basique ce par quoi on obtient un précipité;  (b1) the mixture thus formed is brought into contact with a basic compound whereby a precipitate is obtained;
- (d ) on sépare le précipité du milieu réactionnel et on le calcine.  (d) separating the precipitate from the reaction medium and calcining it.
La première étape de ce procédé met en œuvre une suspension d'un hydroxyde de niobium. Cette suspension peut être obtenue en faisant réagir un sel de niobium, comme un chlorure, avec une base, comme de l'ammoniaque, pour obtenir un précipité d'hydroxyde de niobium. On peut aussi obtenir cette suspension par réaction d'un sel de niobium comme le niobiate de potassium ou de sodium avec un acide comme l'acide nitrique pour obtenir un précipité d'hydroxyde de niobium.  The first step of this process involves a suspension of a niobium hydroxide. This suspension can be obtained by reacting a niobium salt, such as a chloride, with a base, such as ammonia, to obtain a niobium hydroxide precipitate. This suspension can also be obtained by reacting a niobium salt such as potassium or sodium niobate with an acid such as nitric acid to obtain a niobium hydroxide precipitate.
Cette réaction peut se faire dans un mélange d'eau et d'alcool comme de l'éthanol. L'hydroxyde ainsi obtenu est lavé par tout moyen connu et est ensuite remis en suspension dans de l'eau en présence d'un agent peptisant comme l'acide nitrique.  This reaction can be done in a mixture of water and alcohol such as ethanol. The hydroxide thus obtained is washed by any known means and is then resuspended in water in the presence of a peptizing agent such as nitric acid.
La deuxième étape (b1 ) du procédé consiste à mélanger la suspension d'hydroxyde de niobium avec une solution d'un sel de cérium. Cette solution peut contenir en outre un sel de zirconium et aussi de l'élément M dans le cas de la préparation d'une composition qui comprend en outre un oxyde de zirconium ou encore de l'oxyde de zirconium et de cet élément M. Ces sels peuvent être choisis parmi les nitrates, les sulfates, les acétates, les chlorures, le nitrate céri-ammoniacal.  The second step (b1) of the process comprises mixing the suspension of niobium hydroxide with a solution of a cerium salt. This solution may also contain a zirconium salt and also the element M in the case of the preparation of a composition which further comprises a zirconium oxide or else zirconium oxide and this element M. salts may be chosen from nitrates, sulphates, acetates, chlorides, cerium-ammoniac nitrate.
A titre d'exemple de sels de zirconium, on peut ainsi citer le sulfate de zirconium, le nitrate de zirconyle ou le chlorure de zirconyle. Le nitrate de zirconyle est utilisé le plus généralement. Lorsque l'on utilise un sel de cérium sous forme III, il est préférable d'introduire dans la solution des sels un agent oxydant, par exemple de l'eau oxygénée. By way of example of zirconium salts, mention may be made of zirconium sulphate, zirconyl nitrate or zirconyl chloride. Zirconyl nitrate is most commonly used. When a cerium salt in form III is used, it is preferable to introduce into the solution of salts an oxidizing agent, for example hydrogen peroxide.
Les différents sels de la solution sont présents dans les proportions stœchiométriques nécessaires pour obtenir la composition finale désirée.  The different salts of the solution are present in the stoichiometric proportions necessary to obtain the desired final composition.
Le mélange formé à partir de la suspension d'hydroxyde de niobium et de la solution des sels des autres éléments est mis en présence d'un composé basique.  The mixture formed from the niobium hydroxide suspension and the solution of the salts of the other elements is brought into contact with a basic compound.
On peut utiliser comme base ou composé basique les produits du type hydroxyde. On peut citer les hydroxydes d'alcalins ou d'alcalino-terreux. On peut aussi utiliser les aminés secondaires, tertiaires ou quaternaires. Toutefois, les aminés et l'ammoniaque peuvent être préférés dans la mesure où ils diminuent les risques de pollution par les cations alcalins ou alcalino terreux. On peut aussi mentionner l'urée. Le composé basique peut être plus particulièrement utilisé sous forme d'une solution.  Hydroxide products 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 in that they reduce the risk of pollution by alkaline or alkaline earth cations. We can also mention urea. The basic compound may more particularly be used in the form of a solution.
La réaction entre le mélange précité et le composé basique se fait de préférence en continu dans un réacteur. Cette réaction se fait donc en introduisant en continu le mélange et le composé basique et en soutirant en continu aussi le produit de la réaction.  The reaction between the above mixture and the basic compound is preferably continuous in a reactor. This reaction is done by continuously introducing the mixture and the basic compound and continuously withdrawing also the product of the reaction.
Le précipité qui est obtenu est séparé du milieu réactionnel par toute technique classique de séparation solide-liquide telle que par exemple filtration, décantation, essorage ou centrifugation. Ce précipité peut être lavé puis calciné à une température suffisante pour former les oxydes par exemple d'au moins 500°C.  The precipitate which is obtained is separated from the reaction medium by any conventional solid-liquid separation technique such as, for example, filtration, decantation, spinning or centrifugation. This precipitate can be washed and then calcined at a temperature sufficient to form the oxides, for example at least 500 ° C.
Les compositions de l'invention peuvent être encore préparées par un troisième procédé qui comporte les étapes suivantes :  The compositions of the invention may be further prepared by a third method which comprises the following steps:
- (a2) dans une première étape on prépare un mélange en milieu liquide contenant un composé du cérium et, le cas échéant, un composé de zirconium et de l'élément M pour la préparation des compositions qui contiennent de l'oxyde de zirconium ou de l'oxyde de zirconium et un oxyde de l'élément M;  - (a2) in a first step, a mixture in a liquid medium containing a cerium compound and, where appropriate, a zirconium compound and the element M is prepared for the preparation of the compositions which contain zirconium oxide or zirconium oxide and an oxide of the element M;
- (b2) on met en présence ledit mélange et un composé basique, ce par quoi on obtient une suspension contenant un précipité;  (b2) said mixture is brought into contact with a basic compound, whereby a suspension containing a precipitate is obtained;
- (c2) on mélange cette suspension avec une solution d'un sel de niobium;  (c2) this suspension is mixed with a solution of a niobium salt;
- (d2) on sépare le solide du milieu liquide;  - (d2) the solid is separated from the liquid medium;
- (e2) on calcine ledit solide.  - (e2) calcining said solid.
Le composé de cérium peut être un composé de cérium III ou de cérium IV. Les composés sont de préférence des composés solubles tels que des sels. Ce qui a été dit plus haut pour les sels de cérium, de zirconium et de l'élément M s'applique aussi ici. Il en est de même pour la nature du composé basique. Les différents composés du mélange de départ de la première étape sont présents dans les proportions stœchiométriques nécessaires pour obtenir la composition finale désirée. The cerium compound may be a compound of cerium III or cerium IV. The compounds are preferably soluble compounds such as salts. What has been said above for the salts of cerium, zirconium and element M also applies here. It is the same for the nature of the basic compound. The various compounds of the starting mixture of the first step are present in the stoichiometric proportions necessary to obtain the desired final composition.
Le milieu liquide de la première étape est généralement l'eau.  The liquid medium of the first stage is usually water.
Le mélange de départ de la première étape peut être indifféremment obtenu soit à partir de composés initialement à l'état solide que l'on introduira par la suite dans un pied de cuve d'eau par exemple, soit encore directement à partir de solutions de ces composés puis mélange, dans un ordre quelconque, des dites solutions.  The starting mixture of the first step can be indifferently obtained either from compounds initially in the solid state which will be introduced later in a water tank for example, or even directly from solutions of these compounds and then mixing, in any order, said solutions.
L'ordre d'introduction des réactifs dans la deuxième étape (b2) peut être quelconque, le composé basique pouvant être introduit dans le mélange ou inversement ou encore les réactifs pouvant être introduits simultanément dans le réacteur.  The order of introduction of the reagents into the second step (b2) may be arbitrary, the basic compound may be introduced into the mixture or vice versa or the reagents may be introduced simultaneously into the reactor.
L'addition peut être effectuée en une seule fois, graduellement ou en continu, et elle est de préférence réalisée sous agitation. Cette opération peut être conduite à une température comprise entre la température ambiante (18 - 25°C) et la température de reflux du milieu réactionnel, cette dernière pouvant atteindre 120°C par exemple. Elle est de préférence conduite à température ambiante.  The addition can be carried out all at once, gradually or continuously, and it is preferably carried out with stirring. This operation can be conducted at a temperature between room temperature (18-25 ° C) and the reflux temperature of the reaction medium, the latter can reach 120 ° C for example. It is preferably conducted at room temperature.
Comme dans le cas du premier procédé, on peut noter qu'il est possible, notamment dans le cas de l'utilisation d'un composé de cérium III, d'ajouter soit au mélange de départ, soit lors de l'introduction du composé basique un agent oxydant tel que l'eau oxygénée.  As in the case of the first process, it can be noted that it is possible, particularly in the case of the use of a cerium III compound, to add either to the starting mixture or during the introduction of the compound. basic oxidizing agent such as hydrogen peroxide.
A la fin de la deuxième étape (b2) d'addition du composé basique, on peut éventuellement maintenir encore le milieu de réaction sous agitation pendant quelque temps, et ceci afin de parfaire la précipitation.  At the end of the second step (b2) of addition of the basic compound, one can optionally further maintain the reaction medium with stirring for a time, and this in order to complete the precipitation.
Il est aussi possible, à ce stade du procédé d'effectuer un mûrissement. Celui-ci peut être réalisé directement sur le milieu réactionnel obtenu après la mise en présence avec le composé basique ou sur une suspension obtenue après remise dans l'eau du précipité. Le mûrissement se fait en chauffant le milieu. La température à laquelle est chauffé le milieu est d'au moins 40°C, plus particulièrement d'au moins 60°C et encore plus particulièrement d'au moins 100°C. Le milieu est maintenu ainsi à une température constante pendant une durée qui est habituellement d'au moins 30 minutes et plus particulièrement d'au moins 1 heure. Le mûrissement peut se faire à la pression atmosphérique ou éventuellement à une pression plus élevée et à une température supérieure à 100°C et comprise notamment entre 100°C et 150°C. It is also possible at this stage of the process to carry out a ripening. This can be carried out directly on the reaction medium obtained after contacting with the basic compound or on a suspension obtained after returning the precipitate to water. The ripening is done by heating the environment. The temperature at which the medium is heated is at least 40 ° C, more preferably at least 60 ° C and even more preferably at least 100 ° C. The medium is thus maintained at a constant temperature for a period of time which is usually at least 30 minutes and more particularly at least 1 hour. The ripening can be done at atmospheric pressure or possibly at a higher pressure and a temperature above 100 ° C and in particular between 100 ° C and 150 ° C.
L'étape suivante (c2) du procédé consiste à mélanger la suspension obtenue à l'issue de l'étape précédente avec une solution d'un sel de niobium. Comme sel de niobium on peut citer le chlorure de niobium, le niobiate de potassium ou de sodium et tout particulièrement ici l'oxalate de niobium et l'oxalate de niobium et d'ammonium.  The next step (c2) of the process consists in mixing the suspension obtained at the end of the preceding step with a solution of a niobium salt. Niobium salt that may be mentioned niobium chloride, niobate potassium or sodium and especially here niobium oxalate and niobium oxalate and ammonium.
Ce mélange se fait de préférence à température ambiante.  This mixture is preferably at room temperature.
Les étapes suivantes du procédé (d2) et (e2) consistent à séparer le solide de la suspension obtenue à l'étape précédente, à laver éventuellement ce solide puis à le calciner. Ces étapes se déroulent d'une manière identique à ce qui a été décrit plus haut pour le second procédé.  The following steps of the process (d2) and (e2) consist in separating the solid from the suspension obtained in the preceding step, optionally washing this solid and then calcining it. These steps proceed in a manner identical to that described above for the second method.
Dans le cas de la préparation de compositions qui contiennent de l'oxyde de l'élément M le troisième procédé peut présenter une variante dans laquelle le composé de cet élément M n'est pas présent dans l'étape (a2). Le composé de l'élément M est alors apporté à l'étape (c2) soit avant soit après le mélange avec la solution de niobium ou encore en même temps.  In the case of the preparation of compositions which contain the oxide of the element M the third method may have a variant in which the compound of this element M is not present in step (a2). The compound of the element M is then provided in step (c2) either before or after mixing with the niobium solution or at the same time.
Le troisième procédé peut aussi être mis en œuvre selon une autre variante dans laquelle à l'issue de l'étape (c2) on ajoute au milieu issu de cette étape un additif choisi parmi les tensioactifs anioniques, les tensioactifs non ioniques, les polyéthylène-glycols, les acides carboxyliques et leurs sels et les tensioactifs du type éthoxylats d'alcools gras carboxyméthylés. On procède ensuite à l'étape (d2). Il est aussi possible d'effectuer les étapes (c2) et (d2) puis d'ajouter l'additif précité au solide issu de la séparation.  The third method can also be implemented according to another variant in which at the end of step (c2) is added to the medium resulting from this step an additive selected from anionic surfactants, nonionic surfactants, polyethylene- glycols, carboxylic acids and their salts and surfactants of the ethoxylates type of carboxymethylated fatty alcohols. Then proceed to step (d2). It is also possible to carry out the steps (c2) and (d2) and then add the aforementioned additive to the solid resulting from the separation.
En ce qui concerne plus précisément la nature de l'additif on pourra se réfère à la description de WO 2004/085039. Comme tensioactif non ionique on peut mentionner plus particulièrement les produits vendus sous les marques IGEPAL®, DOWANOL®, RHODAMOX® et ALKAMIDE®. En ce qui concerne les acides carboxyliques on peut citer ainsi notamment les acides formique, acétique, proprionique, butyrique, isobutyrique, valérique, caproïque, caprylique, caprique, laurique, myristique, palmitique ainsi que leurs sels ammoniacaux. With regard more specifically to the nature of the additive, reference may be made to the description of WO 2004/085039. As nonionic surfactant may be mentioned more particularly the products sold under the trademark IGEPAL ®, DOWANOL ®, ® and Rhodamox® Alkamide ®. As regards the carboxylic acids, mention may be made in particular of formic, acetic, propionic, butyric, isobutyric, valeric, caproic, caprylic, capric, lauric, myristic and palmitic acids, as well as their ammoniacal salts.
Enfin, les compositions de l'invention qui sont à base des oxydes de cérium, de niobium et de zirconium et éventuellement d'un oxyde de l'élément M peuvent être préparées aussi par un quatrième procédé qui va être décrit ci- dessous.  Finally, the compositions of the invention which are based on the oxides of cerium, niobium and zirconium and optionally an oxide of the element M may also be prepared by a fourth method which will be described below.
Ce procédé comporte les étapes suivantes : - (a3) on prépare un mélange en milieu liquide contenant un composé du zirconium et un composé du cérium et, le cas échéant, de l'élément M; This process comprises the following steps: - (a3) a mixture in liquid medium containing a zirconium compound and a cerium compound and, where appropriate, the element M;
- (b3) on chauffe ledit mélange à une température supérieure à 100°C; - (b3) heating said mixture to a temperature above 100 ° C;
- (c3) on amène le milieu réactionnel obtenu à l'issue du chauffage à un pH basique; (c3) the reaction medium obtained at the end of the heating is brought to a basic pH;
- (c'3) on effectue éventuellement un mûrissement du milieu réactionnel; - (c'3) is optionally carried out a ripening of the reaction medium;
- (d3) on mélange ce milieu avec une solution d'un sel de niobium; (d3) this medium is mixed with a solution of a niobium salt;
- (e3) on sépare le solide du milieu liquide;  - (e3) the solid is separated from the liquid medium;
- (f3) on calcine ledit solide.  - (f3) calcine said solid.
La première étape du procédé consiste à préparer un mélange en milieu liquide d'un composé du zirconium et d'un composé du cérium et, le cas échéant, de l'élément M. Les différents composés du mélange sont présents dans les proportions stœchiométriques nécessaires pour obtenir la composition finale désirée.  The first step of the process consists in preparing a mixture in a liquid medium of a zirconium compound and a cerium compound and, where appropriate, of the element M. The various compounds of the mixture are present in the necessary stoichiometric proportions to obtain the desired final composition.
Le milieu liquide est généralement l'eau.  The liquid medium is usually water.
Les composés sont de préférence des composés solubles. Ce peut être notamment des sels de zirconium, de cérium et de l'élément M tels que décrits plus haut.  The compounds are preferably soluble compounds. This can be in particular salts of zirconium, cerium and element M as described above.
Le mélange peut être indifféremment obtenu soit à partir de composés initialement à l'état solide que l'on introduira par la suite dans un pied de cuve d'eau par exemple, soit encore directement à partir de solutions de ces composés puis mélange, dans un ordre quelconque, des dites solutions.  The mixture can be indifferently obtained either from compounds initially in the solid state which will subsequently be introduced into a water tank for example, or even directly from solutions of these compounds and then mixed in any order, of said solutions.
Le mélange initial étant ainsi obtenu, on procède ensuite, conformément à la deuxième étape (b3) de ce quatrième procédé, à son chauffage.  The initial mixture is thus obtained, then, in accordance with the second step (b3) of this fourth method, it is heated.
La température à laquelle est mené ce traitement thermique, aussi appelé thermohydrolyse, est supérieure à 100°C. Elle peut ainsi être comprise entre 100°C et la température critique du milieu réactionnel, en particulier entre 100 et 350°C, de préférence entre 100 et 200°C.  The temperature at which this heat treatment, also called thermohydrolysis, is carried out is greater than 100 ° C. It can thus be between 100 ° C. and the critical temperature of the reaction medium, in particular between 100 and 350 ° C., preferably between 100 and 200 ° C.
L'opération de chauffage peut être conduite en introduisant le milieu liquide dans une enceinte close (réacteur fermé du type autoclave), la pression nécessaire ne résultant alors que du seul chauffage du milieu réactionnel (pression autogène). Dans les conditions de températures données ci-dessus, et en milieux aqueux, on peut ainsi préciser, à titre illustratif, que la pression dans le réacteur fermé peut varier entre une valeur supérieure à 1 Bar (105 Pa) et 165 Bar (1 ,65. 107 Pa), de préférence entre 5 Bar (5. 105 Pa) et 165 Bar (1 ,65. 107 Pa). Il est bien entendu également possible d'exercer une pression extérieure qui s'ajoute alors à celle consécutive au chauffage. On peut aussi effectuer le chauffage dans un réacteur ouvert pour les températures voisines de 100°C. The heating operation can be carried out by introducing the liquid medium into a closed chamber (autoclave-type closed reactor), the necessary pressure then resulting only from the sole heating of the reaction medium (autogenous pressure). Under the conditions of the temperatures given above, and in aqueous media, it is thus possible to specify, by way of illustration, that the pressure in the closed reactor can vary between a value greater than 1 bar (10 5 Pa) and 165 bar (1 bar). , 65. 10 7 Pa), preferably between 5 Bar (5 × 10 5 Pa) and 165 Bar (1, 65. 10 7 Pa). It is of course also possible to exert an external pressure which is added to that subsequent to heating. It is also possible to carry out heating in an open reactor for temperatures close to 100 ° C.
Le chauffage peut être conduit soit sous air, soit sous atmosphère de gaz inerte, de préférence l'azote.  The heating may be conducted either in air or in an atmosphere of inert gas, preferably nitrogen.
La durée du traitement n'est pas critique, et peut ainsi varier dans de larges limites, par exemple entre 1 et 48 heures, de préférence entre 2 et 24 heures. De même, la montée en température s'effectue à une vitesse qui n'est pas critique, et on peut ainsi atteindre la température réactionnelle fixée en chauffant le milieu par exemple entre 30 minutes et 4 heures, ces valeurs étant données à titre tout à fait indicatif.  The duration of the treatment is not critical, and can thus vary within wide limits, for example between 1 and 48 hours, preferably between 2 and 24 hours. Similarly, the rise in temperature is carried out at a speed which is not critical, and it is thus possible to reach the reaction temperature set by heating the medium for example between 30 minutes and 4 hours, these values being given for all purposes. indicative fact.
A l'issue de cette deuxième étape, on amène le milieu réactionnel ainsi obtenu à un pH basique. Cette opération est effectuée en ajoutant au milieu une base telle que par exemple une solution d'ammoniaque.  At the end of this second step, the reaction medium thus obtained is brought to a basic pH. This operation is performed by adding to the medium a base such as for example an ammonia solution.
Par pH basique on entend une valeur du pH supérieure à 7 et de préférence supérieure à 8.  By basic pH is meant a pH value greater than 7 and preferably greater than 8.
Bien que cette variante ne soit pas préférée, il est possible d'introduire au mélange réactionnel obtenu à l'issue du chauffage, notamment au moment de l'addition de la base, l'élément M notamment sous la forme qui a été décrite plus haut.  Although this variant is not preferred, it is possible to introduce to the reaction mixture obtained at the end of the heating, in particular at the time of addition of the base, the element M in particular in the form which has been described more high.
A l'issue de l'étape de chauffage, on récupère un précipité solide qui peut être séparé de son milieu comme décrit précédemment.  At the end of the heating step, a solid precipitate is recovered which can be separated from its medium as described above.
Le produit tel que récupéré peut ensuite être soumis à des lavages, qui sont alors opérés à l'eau ou éventuellement avec une solution basique, par exemple une solution d'ammoniaque. Le lavage peut être effectué par remise en suspension dans l'eau du précipité et maintien de la suspension ainsi obtenue à une température qui peut aller jusqu'à 100°C. Pour éliminer l'eau résiduelle, le produit lavé peut éventuellement être séché, par exemple à l'étuve ou par atomisation, et ceci à une température qui peut varier entre 80 et 300°C, de préférence entre 100 et 200°C.  The product as recovered can then be subjected to washes, which are then operated with water or optionally with a basic solution, for example an ammonia solution. The washing can be carried out by resuspension in water of the precipitate and maintenance of the suspension thus obtained at a temperature which can go up to 100 ° C. To remove the residual water, the washed product can optionally be dried, for example in an oven or by atomization, and this at a temperature which can vary between 80 and 300 ° C, preferably between 100 and 200 ° C.
Selon une variante particulière de l'invention, le procédé comprend un mûrissement (étape c'3).  According to a particular variant of the invention, the process comprises a ripening (step c'3).
Le mûrissement se fait dans les mêmes conditions que celles qui ont été décrites plus haut pour le troisième procédé.  The ripening is done under the same conditions as those described above for the third method.
Le mûrissement peut aussi s'effectuer sur une suspension obtenue après remise dans l'eau du précipité. On peut ajuster le pH de cette suspension à une valeur supérieure à 7 et de préférence supérieure à 8.  The ripening can also be carried out on a suspension obtained after putting the precipitate back into water. The pH of this suspension can be adjusted to a value greater than 7 and preferably greater than 8.
Il est possible de faire plusieurs mûrissements. Ainsi, on peut remettre en suspension dans l'eau, le précipité obtenu après l'étape de mûrissement et éventuellement un lavage puis effectuer un autre mûrissement du milieu ainsi obtenu. Cet autre mûrissement se fait dans les mêmes conditions que celles qui ont été décrites pour le premier. Bien entendu, cette opération peut être répétée plusieurs fois. It is possible to do several matures. Thus, the precipitate obtained after the ripening stage can be resuspended in water. optionally washing and then perform another ripening of the medium thus obtained. This other ripening is done under the same conditions as those described for the first. Of course, this operation can be repeated several times.
Les étapes suivantes de ce quatrième procédé (d3) à (f3) c'est-à-dire le mélange avec la solution de sel de niobium, la séparation solide/liquide et la calcination, se font de la même manière que pour les étapes correspondantes du second et du troisième procédé. Ce qui a été décrit plus haut pour ces étapes s'applique donc ici.  The following steps of this fourth process (d3) to (f3), that is to say the mixing with the niobium salt solution, the solid / liquid separation and the calcination, are done in the same way as for the steps corresponding of the second and third processes. What has been described above for these steps therefore applies here.
Les compositions de l'invention telles que décrites plus haut, c'est à dire les compositions à base des oxydes de cérium, de niobium et éventuellement de zirconium et de l'élément se présentent sous forme de poudres mais elles peuvent éventuellement être mises en forme pour se présenter sous forme de granulés, billes, cylindres ou nids d'abeille de dimensions variables.  The compositions of the invention as described above, that is to say the compositions based on cerium, niobium and optionally zirconium oxides and the element are in the form of powders, but they may optionally be used. form to be in the form of granules, balls, cylinders or honeycombs of varying sizes.
Ces compositions peuvent être utilisées avec tout matériau employé habituellement dans le domaine de la formulation de catalyseur, c'est à dire notamment un matériau choisi parmi les matériaux inertes thermiquement. Ce matériau peut être choisi parmi l'alumine, l'oxyde de titane, l'oxyde de cérium, l'oxyde de zirconium, la silice, les spinelles, les zéolites, les silicates, les phosphates de silicoaluminium cristallins, les phosphates d'aluminium cristallins.  These compositions may be used with any material usually employed in the field of the catalyst system, that is to say in particular a material chosen from thermally inert materials. This material may be chosen from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinels, zeolites, silicates, crystalline silicoaluminium phosphates, phosphates of crystalline aluminum.
Les compositions de l'invention toujours telles que décrites plus haut peuvent aussi être utilisées dans des systèmes catalytiques comprenant un revêtement (wash coat) à propriétés catalytiques et à base de ces compositions avec un matériau du type de ceux mentionnés plus haut, le revêtement étant déposé sur un substrat du type par exemple monolithe métallique, par exemple FerCralloy, ou en céramique, par exemple en cordiérite, en carbure de silicium, en titanate d'alumine ou en mullite.  The compositions of the invention still as described above can also be used in catalytic systems comprising a coating (wash coat) with catalytic properties and based on these compositions with a material of the type mentioned above, the coating being deposited on a substrate of the type for example metal monolith, for example FerCralloy, or ceramic, for example cordierite, silicon carbide, alumina titanate or mullite.
Ce revêtement est obtenu par mélange de la composition avec le matériau de manière à former une suspension qui peut être ensuite déposée sur le substrat.  This coating is obtained by mixing the composition with the material so as to form a suspension which can then be deposited on the substrate.
Dans le cas des utilisations en catalyse, et notamment dans les systèmes catalytiques précités, les compositions de l'invention peuvent être employées en combinaison avec des métaux précieux, elles peuvent jouer ainsi éventuellement le rôle de support pour ces métaux. La nature de ces métaux et les techniques d'incorporation de ceux-ci dans les compositions sont bien connues de l'homme du métier. Par exemple, les métaux peuvent être le platine, le rhodium, le palladium, l'argent, l'or ou l'iridium, ils peuvent notamment être incorporés aux compositions par imprégnation. In the case of uses in catalysis, and especially in the aforementioned catalytic systems, the compositions of the invention may be used in combination with precious metals, they may thus play the role of support for these metals. The nature of these metals and the techniques for incorporating them into the compositions are well known to those skilled in the art. For example, metals can be the platinum, rhodium, palladium, silver, gold or iridium, they can in particular be incorporated into the compositions by impregnation.
Les systèmes catalytiques et plus particulièrement les compositions de l'invention peuvent trouver de très nombreuses applications.  The catalytic systems and more particularly the compositions of the invention can find very many applications.
Ces systèmes catalytiques et plus particulièrement les compositions de l'invention peuvent trouver de très nombreuses applications. Ils sont ainsi particulièrement bien adaptés à, et donc utilisables dans, la catalyse de diverses réactions telles que, par exemple, la déshydratation, l'hydrosulfuration, l'hydrodénitrification, la désulfuration, l'hydrodésulfuration, la déshydrohalogénation, le reformage, le reformage à la vapeur, le craquage, l'hydrocraquage, l'hydrogénation, la déshydrogénation, l'isomérisation, la dismutation, lOxychloration, la déshydrocyclisation d'hydrocarbures ou autres composés organiques, les réactions d'oxydation et/ou de réduction, la réaction de Claus, le traitement des gaz d'échappement des moteurs à combustion interne, la démétallation, la méthanation, la shift conversion, l'oxydation catalytique des suies émises par les moteurs à combustion interne comme les moteurs diesel ou essence fonctionnant en régime pauvre. Les systèmes et compositions de l'invention peuvent être utilisés comme catalyseurs dans un procédé mettant en œuvre une réaction de gaz à l'eau, une réaction de vapo- réformage, une réaction d'isomérisation ou une réaction de crackage catalytique. Enfin, les systèmes catalytiques et les compositions de l'invention peuvent être utilisés comme pièges à NOx.  These catalytic systems and more particularly the compositions of the invention can find very many applications. They are thus particularly well adapted to, and therefore usable in, the catalysis of various reactions such as, for example, dehydration, hydrosulfuration, hydrodenitrification, desulfurization, hydrodesulfurization, dehydrohalogenation, reforming, reforming. steam, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, disproportionation, oxychlorination, dehydrocyclization of hydrocarbons or other organic compounds, oxidation and / or reduction reactions, reaction of Claus, the treatment of the exhaust gases of internal combustion engines, the demetallation, the methanation, the shift conversion, the catalytic oxidation of soot emitted by internal combustion engines such as diesel or gasoline engines operating in a lean regime. The systems and compositions of the invention can be used as catalysts in a process involving a gas-to-water reaction, a vapor reforming reaction, an isomerization reaction or a catalytic cracking reaction. Finally, the catalyst systems and compositions of the invention can be used as NOx traps.
Les systèmes catalytiques et les compositions de l'invention peuvent être plus particulièrement utilisés dans les applications qui suivent.  The catalyst systems and compositions of the invention may be more particularly used in the following applications.
Une première application concerne un procédé de traitement d'un gaz dans lequel on utilise un système ou une composition de l'invention comme catalyseur d'oxydation du CO et des hydrocarbures contenus dans ce gaz.  A first application relates to a process for treating a gas in which a system or a composition of the invention is used as a catalyst for oxidation of CO and hydrocarbons contained in this gas.
Selon une seconde application, les systèmes et compositions de l'invention peuvent aussi être utilisés pour l'adsorption des NOx, et du CO2 toujours dans le traitement de gaz.  According to a second application, the systems and compositions of the invention can also be used for the adsorption of NOx, and of CO2 still in the gas treatment.
Le gaz qui est traité dans ces deux applications peut être un gaz provenant d'un moteur à combustion interne (mobile ou stationnaire).  The gas that is treated in these two applications may be a gas from an internal combustion engine (mobile or stationary).
Selon une autre application les compositions de l'invention peuvent être utilisées dans la formulation de catalyseurs pour la catalyse trois voies dans le traitement de gaz d'échappement de moteur à essence et les systèmes catalytiques de l'invention peuvent être utilisés pour la mise en œuvre de cette catalyse. Une autre application concerne l'utilisation des systèmes et compositions de l'invention dans un procédé de traitement d'un gaz en vue de décomposer le N2O. According to another application the compositions of the invention can be used in the formulation of catalysts for three-way catalysis in the treatment of gasoline engine exhaust gases and the catalytic systems of the invention can be used for the implementation of of this catalysis. Another application relates to the use of the systems and compositions of the invention in a process for treating a gas with a view to decomposing N 2 O.
On sait que le N2O se trouve en quantité importante dans les gaz émis par certaines installations industrielles. Pour éviter les rejets de N2O, ces gaz sont traités de manière à décomposer le N2O en oxygène et en azote avant d'être rejetés à l'atmosphère. Les systèmes et compositions de l'invention peuvent être utilisés comme catalyseurs pour cette réaction de décomposition tout particulièrement dans un procédé de préparation d'acide nitrique ou d'acide adipique. It is known that N 2 O is found in a large quantity in the gases emitted by certain industrial installations. To avoid N 2 O releases, these gases are treated to decompose N 2 O into oxygen and nitrogen before being released to the atmosphere. The systems and compositions of the invention can be used as catalysts for this decomposition reaction, particularly in a process for preparing nitric acid or adipic acid.
Des exemples vont maintenant être donnés.  Examples will now be given.
EXEMPLE 1 EXAMPLE 1
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 63,0/27,0/10,0.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.0 / 27.0 / 10.0.
On prépare tout d'abord une suspension d'hydroxyde de niobium selon le procédé suivant.  A suspension of niobium hydroxide is first prepared by the following method.
Dans un réacteur de 5 litres équipé d'un agitateur et d'un condenseur, sont introduits 1200 g d'éthanol anhydre. Sous agitation 295 g de poudre de chlorure de niobium (V) sont ajoutés en 20 minutes. 625 g d'éthanol anhydre sont ensuite ajoutés. Le milieu est laissé au repos pendant 12 heures.  In a 5 liter reactor equipped with a stirrer and a condenser, 1200 g of anhydrous ethanol are introduced. While stirring, 295 g of niobium chloride powder (V) are added over 20 minutes. 625 g of anhydrous ethanol are then added. The medium is left standing for 12 hours.
50 g d'eau désionisée sont introduits dans le réacteur et le milieu est porté à reflux à 70°C pendant 1 heure. On laisse refroidir. Cette solution est nommée A.  50 g of deionized water are introduced into the reactor and the medium is refluxed at 70 ° C for 1 hour. Let cool. This solution is named A.
Dans un réacteur de 6 litres muni d'un agitateur, sont introduits 870 g de solution d'ammoniaque (29,8% en NH3). Sous agitation, on introduit en 15 minutes et simultanément toute la solution A et 2250 ml d'eau désionisée. La suspension est récupérée et lavée plusieurs fois par centrifugation. Le centrifugat est nommé B.  In a 6 liter reactor equipped with a stirrer, 870 g of ammonia solution (29.8% of NH 3) are introduced. With stirring, all solution A and 2250 ml of deionized water are introduced in the course of 15 minutes. The suspension is recovered and washed several times by centrifugation. The centrifugate is named B.
Dans un réacteur de 6 litres muni d'un agitateur, on introduit 2,4 litres d'une solution d'acide nitrique 1 mol/l. Sous agitation, le centrifugat B est introduit dans le réacteur. L'agitation est maintenue pendant 12 heures. Le pH est de 0,7. La concentration est de 4,08% en Nb2Os. Cette suspension est nommée C. In a 6 liter reactor equipped with a stirrer, 2.4 liters of a 1 mol / l nitric acid solution are introduced. Under stirring, the centrifugate B is introduced into the reactor. Stirring is maintained for 12 hours. The pH is 0.7. The concentration is 4.08% in Nb 2 Os. This suspension is named C.
On prépare ensuite une solution d'ammoniaque D en introduisant 1040 g d'une solution d'ammoniaque concentrée (29,8% en NH3) dans 6690 g d'eau désionisée. On prépare une solution E en mélangeant 4250 g d'eau désionisée, 1640 g d'une solution de nitrate de cérium (III) (30,32% en CeO2), 1065 g d'une solution d'oxynitrate de zirconium (20,04% en ZrÛ2), 195 g d'une solution d'eau oxygénée (50,30% en H2O2), 1935 g de la suspension C (4,08% en Ν 2θδ). Cette solution E est mise sous agitation. A solution of ammonia D is then prepared by introducing 1040 g of a concentrated ammonia solution (29.8% of NH 3 ) in 6690 g of deionized water. A solution E is prepared by mixing 4250 g of deionized water, 1640 g of a solution of cerium (III) nitrate (30.32% CeO 2 ), 1065 g of a solution of zirconium oxynitrate (20 , 04% ZrO 2 ), 195 g of a solution of hydrogen peroxide (50.30% in H 2 O 2 ), 1935 g of suspension C (4.08% in Ν 2 θ δ ). This solution E is stirred.
Dans un réacteur agité de 4 litres équipé d'une surverse, la solution D et la solution E sont ajoutées simultanément à un débit de 3,2 litres/heure. Après mise en régime de l'installation, le précipité est récupéré dans un fût. Le pH est stable et voisin de 9.  In a stirred reactor of 4 liters equipped with an overflow, solution D and solution E are added simultaneously at a flow rate of 3.2 liters / hour. After putting the system into operation, the precipitate is recovered in a drum. The pH is stable and close to 9.
La suspension est filtrée, le produit solide obtenu est lavé et calciné à The suspension is filtered, the solid product obtained is washed and calcined at
800°C pendant 4 heures. 800 ° C for 4 hours.
EXEMPLE 2 EXAMPLE 2
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 55,1/40,0/4,9.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 55.1 / 40.0 / 4.9.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 978 g  - concentrated ammonia solution: 978 g
- eau désionisée : 6760 g  - deionized water: 6760 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 5000 g  - deionized water: 5000 g
- solution de nitrate de cérium (III) : 1440 g  - solution of cerium (III) nitrate: 1440 g
- solution d'oxynitrate de zirconium : 1580 g  - solution of zirconium oxynitrate: 1580 g
- solution d'eau oxygénée : 172 g  - hydrogen peroxide solution: 172 g
- suspension C : 950 g  - suspension C: 950 g
On procède ensuite comme dans l'exemple 1 . EXEMPLE 3  The procedure is then as in Example 1. EXAMPLE 3
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 54,0/39,1/6,9.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 54.0 / 39.1 / 6.9.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 1024 g  - concentrated ammonia solution: 1024 g
- eau désionisée : 6710 g On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes : - deionized water: 6710 g A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 4580 g  - deionized water: 4580 g
- solution de nitrate de cérium (III) : 1440 g  - solution of cerium (III) nitrate: 1440 g
- solution d'oxynitrate de zirconium : 1580 g  - solution of zirconium oxynitrate: 1580 g
- solution d'eau oxygénée : 172 g  - hydrogen peroxide solution: 172 g
- suspension C : 1370g  - suspension C: 1370g
On procède ensuite comme dans l'exemple 1 . EXEMPLE 4  The procedure is then as in Example 1. EXAMPLE 4
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 77,9/19,5/2,6.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by mass: 77.9 / 19.5 / 2.6.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 966 g  - concentrated ammonia solution: 966 g
- eau désionisée : 6670 g  - deionized water: 6670 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 5620 g  - deionized water: 5620 g
- solution de nitrate de cérium (III) : 2035 g  - solution of cerium (III) nitrate: 2035 g
- solution d'oxynitrate de zirconium : 770 g  zirconium oxynitrate solution: 770 g
- solution d'eau oxygénée : 242 g  - hydrogen peroxide solution: 242 g
- suspension C : 505 g  - suspension C: 505 g
On procède ensuite comme dans l'exemple 1 .  The procedure is then as in Example 1.
EXEMPLE 5 EXAMPLE 5
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 76,6/19,2/4,2.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by mass: 76.6 / 19.2 / 4.2.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 1002 g  - concentrated ammonia solution: 1002 g
- eau désionisée : 6730 g  - deionized water: 6730 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 5290 g  - deionized water: 5290 g
- solution de nitrate de cérium (III) : 2035 g - solution d'oxynitrate de zirconium : 770 g - solution of cerium (III) nitrate: 2035 g zirconium oxynitrate solution: 770 g
- solution d'eau oxygénée : 242 g  - hydrogen peroxide solution: 242 g
- suspension C : 830 g  - suspension C: 830 g
On procède ensuite comme dans l'exemple 1 .  The procedure is then as in Example 1.
EXEMPLE 6 EXAMPLE 6
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 74,2/18,6/7,2.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 74.2 / 18.6 / 7.2.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 1068 g  - concentrated ammonia solution: 1068 g
- eau désionisée : 6650 g  deionized water: 6650 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 4660 g  - deionized water: 4660 g
- solution de nitrate de cérium (III) : 2035 g  - solution of cerium (III) nitrate: 2035 g
- solution d'oxynitrate de zirconium : 770 g  zirconium oxynitrate solution: 770 g
- solution d'eau oxygénée : 242 g  - hydrogen peroxide solution: 242 g
- suspension C : 1470 g  - suspension C: 1470 g
On procède ensuite comme dans l'exemple 1 .  The procedure is then as in Example 1.
EXEMPLE 7 EXAMPLE 7
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 72,1/18,0/9,9.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by mass: 72.1 / 18.0 / 9.9.
On prépare une solution d'oxalate de niobium (V) et d'ammonium par dissolution à chaud de 192 g d'oxalate de niobium (V) et d'ammonium dans 300 g d'eau désionisée.  A solution of niobium oxalate (V) and ammonium is prepared by hot dissolving 192 g of niobium (V) oxalate and ammonium in 300 g of deionized water.
Cette solution est maintenue à 50°C. La concentration de cette solution est 14,2% en Nb2O5. This solution is maintained at 50 ° C. The concentration of this solution is 14.2% Nb 2 O 5 .
Cette solution est ensuite introduite sur une poudre d'un oxyde mixte de cérium et de zirconium (composition massique CeO2/ZrO2 80/20, surface spécifique après calcination à 800°C 4 heures de 59 m2/g) jusqu'à saturation du volume poreux. This solution is then introduced onto a powder of a mixed oxide of cerium and zirconium (mass composition CeO 2 / ZrO 2 80/20, specific surface after calcination at 800 ° C. 4 hours of 59 m 2 / g) to saturation of the pore volume.
La poudre imprégnée est ensuite calcinée à 800°C (palier de 4 heures). EXEMPLE 8 The impregnated powder is then calcined at 800 ° C. (4 hour stage). EXAMPLE 8
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 68,7/17,2/14,1 .  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 68.7 / 17.2 / 14.1.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 1 148 g  - concentrated ammonia solution: 1,148 g
- eau désionisée : 6570 g  - deionized water: 6570 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 3400 g  - deionized water: 3400 g
- solution de nitrate de cérium (III) : 1880 g  - solution of cerium (III) nitrate: 1880 g
- solution d'oxynitrate de zirconium : 710 g  - solution of zirconium oxynitrate: 710 g
- solution d'eau oxygénée : 224 g  - hydrogen peroxide solution: 224 g
- suspension C : 2870 g  - suspension C: 2870 g
On procède ensuite comme dans l'exemple 1 .  The procedure is then as in Example 1.
EXEMPLE 9 EXAMPLE 9
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 96,8/3,2.  This example relates to the preparation of a composition according to the invention comprising cerium oxide and niobium oxide in the respective proportions by mass: 96.8 / 3.2.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 990 g  - concentrated ammonia solution: 990 g
- eau désionisée : 6750 g  - deionized water: 6750 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais sans oxynitrate de zirconium et dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but without zirconium oxynitrate and in the following proportions:
- eau désionisée : 5710 g  - deionized water: 5710 g
- solution de nitrate de cérium (III) : 2540 g  - solution of cerium (III) nitrate: 2540 g
- solution d'eau oxygénée : 298 g  - hydrogen peroxide solution: 298 g
- suspension C : 625 g  - suspension C: 625 g
On procède ensuite comme dans l'exemple 1 . EXEMPLE 10  The procedure is then as in Example 1. EXAMPLE 10
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 91 ,4%/8,6%. On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes : This example relates to the preparation of a composition according to the invention comprising cerium oxide and niobium oxide in the following respective proportions by weight: 91.4% / 8.6%. A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 1 1 10 g  - concentrated ammonia solution: 1 1 10 g
- eau désionisée : 6610 g  - deionized water: 6610 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais sans oxynitrate de zirconium et dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but without zirconium oxynitrate and in the following proportions:
- eau désionisée : 4570 g  - deionized water: 4570 g
- solution de nitrate de cérium (III) : 2540 g  - solution of cerium (III) nitrate: 2540 g
- solution d'eau oxygénée : 298 g  - hydrogen peroxide solution: 298 g
- suspension C : 1775 g  - suspension C: 1775 g
On procède ensuite comme dans l'exemple 1 .  The procedure is then as in Example 1.
EXEMPLE 1 1 EXAMPLE 1 1
Cet exemple concerne la préparation d'une composition selon l'invention comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 63,0/27,0/10,0.  This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.0 / 27.0 / 10.0.
Une solution de nitrates de zirconium et de cérium IV est préparée par mélange de 264 g d'eau désionisée, de 238 g de solution de nitrate de cérium (IV) (252 g/L en CeÛ2) et de 97 grammes de solution d'oxynitrate de zirconium (261 g/l en ZrÛ2). La concentration de cette solution est 120 g/l en oxyde. A solution of zirconium nitrates and cerium IV is prepared by mixing 264 g of deionized water, 238 g of cerium (IV) nitrate solution (252 g / L in CeO 2 ) and 97 grams of sodium hydroxide solution. zirconium oxynitrate (261 g / l in ZrO 2 ). The concentration of this solution is 120 g / l of oxide.
Dans un réacteur agité de 1 ,5 I on introduit 373 g d'eau désionisée et 1 1 1 g de solution d'ammoniaque (32% en NH3). 1.53 g of deionized water and 11 g of ammonia solution (32% of NH 3 ) are introduced into a stirred reactor of 1.5 liters.
On introduit en 1 heure la solution de nitrates. Le pH final est voisin de 9,5.  The nitrate solution is introduced in one hour. The final pH is around 9.5.
La suspension ainsi préparée est mûrie à 95°C pendant 2 heures. On laisse ensuite refroidir le milieu.  The suspension thus prepared is cured at 95 ° C. for 2 hours. The medium is then allowed to cool.
Une solution d'oxalate de niobium (V) est préparée par dissolution à chaud de 44,8 g d'oxalate de niobium (V) dans 130 g d'eau désionisée.  A solution of niobium oxalate (V) is prepared by hot dissolving 44.8 g of niobium oxalate (V) in 130 g of deionized water.
Cette solution est maintenue à 50°C. La concentration de cette solution est 3,82% en Nb2O5. This solution is maintained at 50 ° C. The concentration of this solution is 3.82% in Nb 2 O 5 .
La solution d'oxalate de niobium (V) est introduite en 20 minutes sur la suspension refroidie.  The solution of niobium oxalate (V) is introduced in 20 minutes on the cooled suspension.
La suspension est filtrée et lavée.  The suspension is filtered and washed.
Le gâteau est ensuite introduit dans un four et calciné à 800°C (palier de The cake is then introduced into an oven and calcined at 800.degree.
4 heures). EXEMPLE 12 4 hours). EXAMPLE 12
Cet exemple concerne la préparation d'une composition comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse 63,3/26,7/10,0.  This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight 63.3 / 26.7 / 10.0.
Une solution de nitrates de zirconium et de cérium IV est préparée par mélange de 451 g d'eau désionisée, de 206 g de solution de nitrate de cérium (IV) (252 g/l en CeÛ2) et de 75 g de solution d'oxynitrate de zirconium (288 g/l en ZrÛ2). La concentration de cette solution est 80 g/l en oxyde. A solution of nitrates of zirconium and cerium IV is prepared by mixing 451 g of deionized water, 206 g of cerium (IV) nitrate solution (252 g / l of CeO 2 ) and 75 g of sodium nitrate solution. zirconium oxynitrate (288 g / l ZrO 2 ). The concentration of this solution is 80 g / l of oxide.
Cette solution de nitrates est introduite dans un autoclave.  This solution of nitrates is introduced into an autoclave.
La température est montée à 100°C. Le milieu est maintenu sous agitation à 100°C pendant 1 heure.  The temperature is raised to 100 ° C. The medium is stirred at 100 ° C. for 1 hour.
On laisse refroidir.  Let cool.
On transfère la suspension dans un réacteur agité de 1 ,5 I.  The suspension is transferred to a stirred reactor of 1.5 liters.
On introduit sous agitation une solution d'ammoniaque 6 mol/l jusqu'à obtenir un pH voisin de 9,5.  6mol / l of ammonia solution is introduced under stirring until a pH in the region of 9.5 is obtained.
La suspension est mûrie à 95°C pendant 2 heures.  The suspension is cured at 95 ° C for 2 hours.
On laisse ensuite refroidir le milieu.  The medium is then allowed to cool.
Une solution d'oxalate de niobium (V) est préparée par dissolution à chaud de 39 g d'oxalate de niobium (V) dans 1 13 g d'eau désionisée.  A solution of niobium oxalate (V) is prepared by hot dissolving 39 g of niobium oxalate (V) in 13 g of deionized water.
Cette solution est maintenue à 50°C. La concentration de cette solution est 3,84% en Nb2O5. This solution is maintained at 50 ° C. The concentration of this solution is 3.84% in Nb 2 O 5 .
La solution d'oxalate de niobium (V) est introduite en 20 minutes sur la suspension refroidie.  The solution of niobium oxalate (V) is introduced in 20 minutes on the cooled suspension.
Le pH est ensuite remonté à pH 9 par ajout d'une solution d'ammoniaque (32% en NH3). The pH is then raised to pH 9 by adding an ammonia solution (32% NH 3 ).
La suspension est filtrée et lavée. Le gâteau est ensuite introduit dans un four et calciné à 800°C (palier de 4 heures).  The suspension is filtered and washed. The cake is then introduced into an oven and calcined at 800 ° C. (4 hour stage).
EXEMPLE 13 EXAMPLE 13
Cet exemple concerne la préparation d'une composition comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 64,0/27,0/9,0.  This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 64.0 / 27.0 / 9.0.
On procède de la même manière que dans l'exemple 12.  The procedure is the same as in Example 12.
Toutefois la solution d'oxalate de niobium (V) est préparée par dissolution à chaud de 35,1 g d'oxalate de niobium (V) dans 1 13 g d'eau désionisée. La concentration de cette solution est 3,45% en Nb2Os. EXEMPLE COMPARATIF 14 However, the solution of niobium oxalate (V) is prepared by hot dissolving 35.1 g of niobium oxalate (V) in 13 g of deionized water. The concentration of this solution is 3.45% Nb 2 O 5. COMPARATIVE EXAMPLE 14
Cet exemple concerne la préparation d'une composition comprenant de l'oxyde de cérium, de l'oxyde de zirconium et de l'oxyde de niobium dans les proportions respectives suivantes en masse : 19,4/77,6/3,0.  This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 19.4 / 77.6 / 3.0.
On prépare une solution d'ammoniaque D comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution of ammonia D is prepared as in Example 1 and with the same compounds but in the following proportions:
- solution d'ammoniaque concentrée : 940 g  - concentrated ammonia solution: 940 g
- eau désionisée : 6730 g  - deionized water: 6730 g
On prépare aussi une solution E comme dans l'exemple 1 et avec les mêmes composés mais dans les proportions suivantes :  A solution E is also prepared as in Example 1 and with the same compounds but in the following proportions:
- eau désionisée : 5710 g  - deionized water: 5710 g
- solution de nitrate de cérium (III) : 2540 g  - solution of cerium (III) nitrate: 2540 g
- solution d'eau oxygénée : 298 g  - hydrogen peroxide solution: 298 g
- suspension C : 625 g  - suspension C: 625 g
On procède ensuite comme dans l'exemple 1 .  The procedure is then as in Example 1.
On mentionne dans le tableau qui suit pour chacune des compositions des exemples ci-dessus : The following table gives for each of the compositions examples above:
- la surface spécifique BET après calcination 4 heures à 800°C et 900°C ; - les propriétés d'acidité;  the BET specific surface area after calcination for 4 hours at 800 ° C. and 900 ° C .; - the acidity properties;
- les propriétés de réductibilité.  - the properties of reducibility.
Acidité Acidity
Les propriétés d'acidité sont mesurées par la méthode TPD qui est décrite ci-dessous.  The acidity properties are measured by the TPD method which is described below.
La molécule sonde utilisée pour caractériser les sites acides en TPD est l'ammoniac.  The probe molecule used to characterize acid sites in TPD is ammonia.
- Préparation de l'échantillon :  - Preparation of the sample:
L'échantillon est porté à 500°C sous flux d'hélium (30 ml/mn) selon une montée en température de 20°C/min et est maintenu à cette température durant 30 minutes afin d'enlever la vapeur d'eau et éviter ainsi d'obturer les pores. Finalement l'échantillon est refroidi jusqu'à 100°C sous flux d'hélium à raison de 10°C/min.  The sample is heated to 500 ° C. under a stream of helium (30 ml / min) according to a rise in temperature of 20 ° C./min and is maintained at this temperature for 30 minutes in order to remove the water vapor and avoid puncturing the pores. Finally the sample is cooled to 100 ° C under a stream of helium at 10 ° C / min.
- Adsorption :  - Adsorption:
L'échantillon est ensuite soumis à un flux (30 ml/mn) d'ammoniac (5% vol de NH3 dans l'hélium à 100°C) à pression atmosphérique pendant 30 minutes (jusqu'à saturation). L'échantillon est soumis durant 1 heure minimum à un flux d'hélium. - Désorption : The sample is then subjected to a flux (30 ml / min) of ammonia (5% vol of NH 3 in helium at 100 ° C) at atmospheric pressure for 30 minutes (until saturation). The sample is subjected for a minimum of 1 hour to a stream of helium. - Desorption:
La TPD est menée en effectuant une montée en température de 10°C/min jusqu'à atteindre 700°C.  TPD is conducted by raising the temperature by 10 ° C / min to 700 ° C.
Durant la montée en température on enregistre la concentration des espèces désorbées, c'est-à-dire de l'ammoniac. La concentration d'ammoniac lors de la phase de désorption est déduite grâce à la calibration de la variation de la conductivité thermique du flux gazeux mesurée en sortie de la cellule à l'aide d'un détecteur de conductivité thermique (TCD).  During the rise in temperature, the concentration of the desorbed species, that is to say ammonia, is recorded. The ammonia concentration during the desorption phase is deduced by calibrating the variation of the thermal conductivity of the gas flow measured at the outlet of the cell using a thermal conductivity detector (TCD).
Dans le tableau 1 les quantités d'ammoniac sont exprimées en ml (conditions normales de température et de pression)/m2 (surface à 800°C) de composition. In Table 1 the amounts of ammonia are expressed in ml (normal conditions of temperature and pressure) / m 2 (area at 800 ° C) of composition.
Plus la quantité d'ammoniac est élevée plus l'acidité de surface du produit est élevée. Réductibilité  The higher the amount of ammonia, the higher the surface acidity of the product. reductibility
Les propriétés de réductibilité sont mesurées en effectuant une réduction en température programmée (TPR) sur un appareil Micromeritics Autochem 2. Cet appareil permet de mesurer la consommation d'hydrogène d'une composition en fonction de la température.  The reducibility properties are measured by performing a programmed temperature reduction (TPR) on a Micromeritics Autochem 2. This meter measures the hydrogen consumption of a composition as a function of temperature.
Plus précisément, on utilise l'hydrogène comme gaz réducteur à 10% en volume dans l'argon avec un débit de 30 ml/mn.  More precisely, hydrogen is used as a reducing gas at 10% by volume in argon with a flow rate of 30 ml / min.
Le protocole expérimental consiste à peser 200 mg de l'échantillon dans un récipient préalablement taré.  The experimental protocol consists in weighing 200 mg of the sample in a previously tared container.
L'échantillon est ensuite introduit dans une cellule en quartz contenant dans le fond de la laine de quartz. L'échantillon est enfin recouvert de laine de quartz et positionné dans le four de l'appareil de mesure.  The sample is then introduced into a quartz cell containing in the bottom of the quartz wool. The sample is finally covered with quartz wool and positioned in the oven of the measuring device.
Le programme de température est le suivant :  The temperature program is as follows:
- montée en température de la température ambiante jusqu'à 900°C avec une rampe de montée à 20°C/mn sous H2 à 10%vol dans Ar. - rise in temperature from room temperature to 900 ° C with a ramp up to 20 ° C / min under H 2 to 10% vol in Ar.
Lors de ce programme, la température de l'échantillon est mesurée à l'aide d'un thermocouple placé dans la cellule de quartz au-dessus de l'échantillon.  In this program, the temperature of the sample is measured using a thermocouple placed in the quartz cell above the sample.
La consommation d'hydrogène lors de la phase de réduction est déduite grâce à la calibration de la variation de la conductivité thermique du flux gazeux mesurée en sortie de la cellule à l'aide d'un détecteur de conductivité thermique (TCD).  Hydrogen consumption during the reduction phase is deduced by calibrating the variation of the thermal conductivity of the gas stream measured at the outlet of the cell using a thermal conductivity detector (TCD).
La consommation d'hydrogène est mesurée entre 30°C et 900°C.  The hydrogen consumption is measured between 30 ° C and 900 ° C.
Elle est reportée dans le tableau 1 en ml (conditions normales de température et de pression) de H2 par g de produit. Plus cette consommation d'hydrogène est élevée, meilleures sont les propriétés de réductibilité du produit (propriétés redox). It is reported in Table 1 in ml (normal conditions of temperature and pressure) of H 2 per g of product. The higher the hydrogen consumption, the better the reducibility properties of the product (redox properties).
Tableau 1  Table 1
Exemple N° Surface spécifique m2/g TPD TPR Ce/Zr/Nb en % ml/m2 ml H2/g EXAMPLE No. Specific Surface Area m 2 / g TPD TPR Ce / Zr / Nb in% ml / m 2 ml H 2 / g
(acidité) (réductibilité) (acidity) (reducibility)
800°C 900°C 1000°C 800 ° C 900 ° C 1000 ° C
N°1 35 17 4 6,5.10"2 32,9N ° 1 35 17 4 6,5.10 "2 32,9
63,0/27,0/10,0 63.0 / 27.0 / 10.0
N°2 41 19 7,8 6,4.10"2 29,7 55,1/40,0/4,9 N ° 2 41 19 7,8 6,4,10 "2 29,7 55,1 / 40,0 / 4,9
N°3 38 16 6,2 7,3.10"2 29,4 54,0/39,1/6,9 N ° 3 38 16 6.2 7.3.10 "2 29.4 54.0 / 39.1 / 6.9
N°4 37 12 5,8 8,7.10"2 30,7 77,9/19,5/2,6 N ° 4 37 12 5.8 8.7.10 "2 30.7 77.9 / 19.5 / 2.6
N°5 30 14 5,6 6,9.10"2 29,8 76,6/19,2/4,2 No. 5 30 14 5.6 6.9.10 "2 29.8 76.6 / 19.2 / 4.2
N°6 28 15 3,9 9,4.10"2 32,3 74,2/18,6/7,2 N ° 6 28 15 3.9 9.4.10 "2 32.3 74.2 / 18.6 / 7.2
N°7 31 17 3,7 8,3.10"2 32,5 72,1/18,0/9,9 Nr. 7 31 17 3.7 8.3 x 2 32.5 72.1 / 18.0 / 9.9
N°8 32 12 3,9 7,8.10"2 33,9 68,7/17,2/14,1 N ° 8 32 12 3.9 7.8.10 "2 33.9 68.7 / 17.2 / 14.1
N°9 19 15 4,5 9,1 .10"2 19,5 96,8/0/3,2 No. 9 19 15 4.5 9.1 .10 "2 19.5 96.8 / 0 / 3.2
N°10 34 15 4,1 8,9.10"2 21 91 ,4/0/8,6 No. 10 34 15 4.1 8.9.10 "2 21 91, 4/0 / 8.6
N°1 1 36 16 4,3 7,5.10"2 30,4 63,0/27,0/10,0 No. 1 1 36 16 4.3 7.5.10 "2 30.4 63.0 / 27.0 / 10.0
N°12 47 15 4 7.10"2 31 ,0 63,3/26,7/10,0 No. 12 47 15 4 7.10 "2 31, 0 63.3 / 26.7 / 10.0
N°13 48 16 4 7.10"2 31 ,2 64,0/27,0/9,0 N ° 13 48 16 4 7.10 "2 31, 2 64.0 / 27.0 / 9.0
N°14 52 31 4,1 7,6.10"2 12,6 comparatif N ° 14 52 31 4.1 7.6.10 "2 12.6 comparative
19,4/77,6/3,0 Il est rappelé que les valeurs de réductibilité du tableau sont données pour des compositions ayant subi une calcination à 800°C pendant 4 heures. 19.4 / 77.6 / 3.0 It is recalled that the reducibility values of the table are given for compositions having undergone calcination at 800 ° C. for 4 hours.
On voit à partir du tableau 1 que les compositions selon l'invention présentent à la fois de bonnes propriétés de réductibilité et d'acidité. La composition de l'exemple comparatif présente de bonnes propriétés d'acidité mais les propriétés de réductibilité sont très inférieures à celles des compositions de l'invention.  It can be seen from Table 1 that the compositions according to the invention have both good properties of reducibility and acidity. The composition of the comparative example has good acidity properties but the reducibility properties are much lower than those of the compositions of the invention.

Claims

REVENDICATIONS
1 - Composition à base d'oxyde de céhum, caractérisée en ce qu'elle comprend de l'oxyde de niobium avec les proportions suivantes en masse :1 - composition based on cuminal oxide, characterized in that it comprises niobium oxide with the following proportions by mass:
- oxyde de niobium de 2 à 20%; niobium oxide of 2 to 20%;
le complément en oxyde de cérium. the complement in cerium oxide.
2- Composition selon la revendication 1 , caractérisée en ce qu'elle comprend en outre de l'oxyde de zirconium avec les proportions suivantes en masse :2- Composition according to claim 1, characterized in that it further comprises zirconium oxide with the following proportions by mass:
- oxyde de cérium au moins 50%; - cerium oxide at least 50%;
- oxyde de niobium de 2 à 20%;  niobium oxide of 2 to 20%;
- oxyde de zirconium jusqu'à 48%. 3- Composition selon la revendication 2, caractérisée en ce qu'elle comprend en outre au moins un oxyde d'un élément M choisi dans le groupe comprenant le tungstène, le molybdène, le fer, le cuivre, le silicium, l'aluminium, le manganèse, le titane, le vanadium et les terres rares autres que le cérium, avec les proportions suivantes en masse :  zirconium oxide up to 48%. 3- Composition according to claim 2, characterized in that it further comprises at least one oxide of an element M selected from the group consisting of tungsten, molybdenum, iron, copper, silicon, aluminum, manganese, titanium, vanadium and rare earths other than cerium, with the following proportions by mass:
- oxyde de cérium au moins 50%; - cerium oxide at least 50%;
- oxyde de niobium de 2 à 20%;  niobium oxide of 2 to 20%;
- oxyde de l'élément M : jusqu'à 20%;  oxide of the element M: up to 20%;
- le complément en oxyde de zirconium. 4- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle présente après calcination 4 heures à 800°C une acidité d'au moins 6.10"2, plus particulièrement d'au moins 7.10"2, cette acidité étant exprimée en ml d'ammoniac par m2 de composition. 5- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle comprend de l'oxyde de niobium dans une proportion en masse comprise entre 3% et 15%. the zirconium oxide supplement. 4- Composition according to one of the preceding claims, characterized in that it has after calcination for 4 hours at 800 ° C an acidity of at least 6.10 "2 , more particularly at least 7.10 " 2 , this acidity being expressed in ml of ammonia per m 2 of composition. 5. Composition according to one of the preceding claims, characterized in that it comprises niobium oxide in a mass proportion of between 3% and 15%.
6- Composition selon l'une des revendications 2 ou 3, caractérisée en ce qu'elle comprend de l'oxyde de cérium dans une proportion en masse d'au moins 65% et de l'oxyde de niobium dans une proportion en masse comprise entre 2 et 12% et plus particulièrement entre 2 et 10%. 7- Composition selon la revendication 6, caractérisée en ce qu'elle comprend de l'oxyde de cérium dans une proportion en masse d'au moins 70% et plus particulièrement d'au moins 75%. 8- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle comprend de l'oxyde de niobium dans une proportion en masse inférieure à 10% et plus particulièrement comprise entre 2% et 10%, cette valeur étant exclue. 9- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle présente une acidité mesurée par analyse TPD d'au moins d'au moins 6.10"2 et plus particulièrement d'au moins 6,4. 10"2 ml d'ammoniac par m2. 6. Composition according to one of claims 2 or 3, characterized in that it comprises cerium oxide in a proportion by mass of at least 65% and niobium oxide in a proportion by mass included between 2 and 12% and more particularly between 2 and 10%. 7- Composition according to claim 6, characterized in that it comprises cerium oxide in a mass proportion of at least 70% and more particularly at least 75%. 8- Composition according to one of the preceding claims, characterized in that it comprises niobium oxide in a proportion by weight less than 10% and more particularly between 2% and 10%, this value being excluded. 9- Composition according to one of the preceding claims, characterized in that it has an acidity measured by TPD analysis of at least at least 6.10 -2 and more particularly at least 6.4 10 -2 ml. of ammonia per m 2 .
10- Composition selon l'une des revendications 1 ou 4 à 9 en combinaison avec la revendication 1 caractérisée en ce qu'elle présente après calcination10- Composition according to one of claims 1 or 4 to 9 in combination with claim 1 characterized in that it has after calcination
4 heures à 800°C qui est d'au moins 15 m2/g. 4 hours at 800 ° C which is at least 15 m 2 / g.
1 1 - Composition selon l'une des revendications 2, 3 ou 4 à 9 en combinaison avec la revendication 2, caractérisée en ce qu'elle présente après calcination 4 heures à 800°C qui est d'au moins 20 m2/g. 1 1 - Composition according to one of claims 2, 3 or 4 to 9 in combination with claim 2, characterized in that it has after calcination for 4 hours at 800 ° C which is at least 20 m 2 / g .
12- Composition selon l'une des revendications précédentes, caractérisée en ce qu'elle présente après calcination à 1000°C 4 heures d'au moins 2 m2/g, plus particulièrement d'au moins 3 m2/g. 12- Composition according to one of the preceding claims, characterized in that it has after calcination at 1000 ° C 4 hours of at least 2 m 2 / g, more particularly at least 3 m 2 / g.
13- Système catalytique, caractérisé en ce qu'il comprend une composition selon l'une des revendications 1 à 12. 13- catalytic system, characterized in that it comprises a composition according to one of claims 1 to 12.
14- Procédé de traitement d'un gaz, plus particulièrement d'un gaz d'échappement d'un moteur, caractérisé en ce qu'on utilise comme catalyseur d'oxydation du CO et des hydrocarbures contenus dans ce gaz un système catalytique selon la revendication 13 ou une composition selon l'une des revendications 1 à 12. 15- Procédé de traitement d'un gaz, caractérisé en ce qu'on utilise un système catalytique selon la revendication 13 ou une composition selon l'une des revendications 1 à 12 pour la décomposition du N2O, pour l'adsorption des NOx et du CO2. 16- Procédé mettant en œuvre une des réactions suivantes : réaction de gaz à l'eau, réaction de vapo-réformage, réaction d'isomérisation, réaction de crackage catalytique, caractérisé en ce qu'on utilise un système catalytique selon la revendication 13 ou une composition selon l'une des revendications 1 à 12. 14. A method for treating a gas, more particularly an engine exhaust gas, characterized in that a catalytic system according to the invention is used as the oxidation catalyst for CO and the hydrocarbons contained therein. claim 13 or a composition according to one of claims 1 to 12. 15- Process for treating a gas, characterized in that a catalytic system according to claim 13 or a composition according to one of claims 1 to 12 for the decomposition of N 2 O, for the adsorption of NOx and CO 2 . 16- Process implementing one of the following reactions: reaction of gas with water, vapor reforming reaction, isomerization reaction, catalytic cracking reaction, characterized in that a catalytic system according to claim 13 or a composition according to one of claims 1 to 12.
17- Procédé de catalyse trois voies pour le traitement de gaz d'échappement de moteur à essence caractérisé en ce qu'on utilise un système catalytique selon la revendication 13 pour la mise en œuvre de ce procédé ou un catalyseur formulé à partir d' une composition selon l'une des revendications 1 à 12. 17- A three-way catalytic process for the treatment of gasoline engine exhaust gas, characterized in that a catalytic system according to claim 13 for the implementation of this method or a catalyst formulated from a catalyst is used. Composition according to one of Claims 1 to 12.
EP11731313.0A 2010-07-07 2011-07-05 Composition based on oxides of cerium, of niobium and, optionally, of zirconium and use thereof in catalysis Withdrawn EP2590737A1 (en)

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