WO1999041009A1 - Method for treating a cerium oxide based composition to increase said composition oxygen-storing capacity - Google Patents

Method for treating a cerium oxide based composition to increase said composition oxygen-storing capacity Download PDF

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Publication number
WO1999041009A1
WO1999041009A1 PCT/FR1999/000334 FR9900334W WO9941009A1 WO 1999041009 A1 WO1999041009 A1 WO 1999041009A1 FR 9900334 W FR9900334 W FR 9900334W WO 9941009 A1 WO9941009 A1 WO 9941009A1
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Prior art keywords
composition
oxygen
cerium oxide
treatment
impurity
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PCT/FR1999/000334
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French (fr)
Inventor
Marco Daturi
Jean-Claude Lavalley
José RODRIGUEZ-IZQUIERDO
Jan Kaspar
Hilario Vidal Munoz
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Rhodia Chimie
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Priority to AU24299/99A priority Critical patent/AU2429999A/en
Publication of WO1999041009A1 publication Critical patent/WO1999041009A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C11/00—Use of gas-solvents or gas-sorbents in vessels
    • 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
    • B01D53/02—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 by adsorption, e.g. preparative gas chromatography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • 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
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
    • 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
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/10—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of rare earths
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • 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
    • B01J37/12—Oxidising
    • B01J37/14—Oxidising with gases containing free oxygen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general

Definitions

  • the present invention relates to a process for treating a composition based on cerium oxide or a mixture of cerium oxide and zirconium oxide, in order to increase the oxygen storage capacity of this composition.
  • multifunctional catalysts are used for the treatment of exhaust gases from internal combustion engines (automotive post-combustion catalysis).
  • Multifunctional means the catalysts capable of carrying out not only the oxidation in particular of carbon monoxide and of the hydrocarbons present in the exhaust gases but also the reduction of the nitrogen oxides also present in these gases (catalysts "three ways ").
  • Compositions based on cerium oxide or on a mixture of cerium oxide and zirconium oxide appear today to be particularly important and advantageous for this type of catalyst.
  • these catalysts must provide buffering power against variations in the oxygen content of the gas mixture to be treated.
  • This buffering capacity is evaluated by the capacity to store oxygen in an oxidizing medium and to restore it in a reducing medium. Being able to improve this oxygen storage capacity therefore presents a certain interest for catalysts of this type.
  • the object of the invention is a process which makes it possible to obtain such an improvement from certain catalytic compositions.
  • the method according to the invention for treating a composition based on cerium oxide or on a mixture of cerium oxide and zirconium oxide is characterized in that it is subjected to a treatment thermal at a temperature of at least 600 ° C., in the presence of oxygen, a composition which has at least one impurity of the carbonate, chloride, sulfate, oxalate or citrate type, in a content of at least 0.1% weight expressed as anion of impurity relative to the whole of the composition.
  • compositions to which the process of the invention applies are those based on cerium oxide alone, or on a mixture of cerium oxide and 2 zirconium.
  • compositions well suited to the application in catalysis will be used, that is to say compositions with a sufficient specific surface.
  • cerium and zirconium-based compositions these can correspond in particular to the overall formula Ce-
  • x Zr x ⁇ 2 in which x satisfies the relation 0 ⁇ x ⁇ 0.95. More particularly, x can verify the relation 0.1 ⁇ x ⁇ 0.6 and, even more particularly, 0.2 ⁇ x ⁇ 0.5.
  • compositions are prepared in a known manner, for example by precipitation from cerium and zirconium salts.
  • the process of the invention applies to compositions which have a certain content of impurities.
  • impurities can be carbonates, chlorides, sulfates, oxalates or citrates or mixtures of these.
  • These impurities generally come from the precursors of cerium and zirconium oxides used in the preparation of the compositions.
  • the impurity content is at least 0J%. This content is expressed, here and for the whole of the description, in% by weight of impurity anion relative to the whole of the composition. This content can more particularly be at least 0.3% and even more particularly at least 1%.
  • the composition based on cerium oxide or on a mixture of cerium oxide and zirconium oxide, and capable of being treated by the process of the invention can comprise an additive, in particular by to improve the stability of the specific surface.
  • This additive can be chosen, alone or as a mixture, from rare earths; alkaline earths; aluminum; molybdenum; scandium; silicon; gallium; titanium; vanadium; niobium; tantalum.
  • rare earth is meant the elements of the group consisting of yttrium and the elements of the periodic classification with atomic number between 57 and 71 inclusive.
  • rare earths mention may be made in particular of yttrium, lanthanum, neodymium and praseodymium.
  • the heat treatment of the invention is done in the presence of oxygen.
  • the atmosphere in which the process of the invention is carried out can be either pure oxygen or oxygen in another gas which can be an inert gas, preferably nitrogen.
  • air this air possibly being more or less depleted in oxygen.
  • the partial oxygen pressure can vary over a wide range. It is usually between 10 ⁇ Pa and 2.1.10 ⁇ Pa. It can be at most 10 4 Pa and more particularly between 2.1 ⁇ 3pa and 10 4 Pa.
  • the treatment can also be carried out in an atmosphere containing water, for example at a partial pressure of water d '' at least 10 3 Pa.
  • the processing temperature is at least 600 ° C. Generally, it will be between 600 ° C and 900 ° C. A rise in temperature increases 3 generally the effectiveness of treatment. However, too high a temperature could modify the properties of the treated composition and in particular have an unfavorable influence on its specific surface.
  • the treatment temperature also depends on the type of impurity present in the composition to be treated. Thus, in the case of nitrates or carbonates impurities, this temperature can be between 600 ° C and 750 ° C, more particularly between 650 ° C and 750 ° C. In the case of sulfates, it is preferably placed at a temperature of at least 800 ° C., more particularly of at least 850 ° C. By working in the presence of water, the treatment temperature can be lowered. The duration of treatment can vary within wide limits.
  • the heat treatment is implemented by observing stages during the rise in temperature of the ambient to the temperature at which the treatment must take place.
  • the number of steps can be arbitrary. For example, for a processing temperature of 850 ° C, one can observe a plateau at 100 ° C and 300 ° C.
  • the duration of the landing can be approximately one hour. It is also possible, in the case where stages are carried out, to carry out a treatment under vacuum of the composition, at the end of at least one stage and before continuing the rise in temperature. This vacuum treatment is done at bearing temperature. The duration of this vacuum treatment can be approximately one hour. After the vacuum treatment, the oxygen treatment is continued by increasing the temperature.
  • compositions obtained have an improved oxygen storage capacity compared to the untreated compositions. This makes them particularly suitable for the treatment of exhaust gases from internal combustion engines. Examples will now be given. Description of the test making it possible to quantify the storage of oxygen
  • the buffering capacity of a composition with respect to oxygen is evaluated by its capacity to store oxygen in an oxidizing medium and to restore it in a reducing medium.
  • the test evaluates the capacity of the composition to successively oxidize determined quantities of carbon monoxide of oxygen and to consume determined quantities of oxygen to reoxidize the composition. The method used is said to be alternate.
  • the carrier gas is pure helium at a flow rate of 10 / h.
  • the injections are made via a loop containing 16ml of gas.
  • the quantities of CO are supplied using a gaseous mixture containing 5% of CO diluted in helium while the quantities of O 2 are supplied from a gaseous mixture containing 2.5% of diluted O 2 in helium.
  • the gas analysis is carried out by chromatography using a thermal conductivity detector.
  • the amount of oxygen consumed determines the oxygen storage capacity (OSC).
  • OSC oxygen storage capacity
  • the characteristic value of the oxygen storage capacity is expressed in ml of oxygen (under normal temperature and pressure conditions) per gram of product introduced and it is measured at 400 ° C.
  • This example relates to the preparation of a mixed oxide of formula Ce 0 , 62Z o, 38 ⁇ 2-
  • a mixed oxide of formula identical to that of Example 1 is prepared.
  • Example 2 The procedure is as in Example 1, except for the final calcination step which is carried out at the temperature of 850 ° C. for 5 hours in an atmosphere of nitrogen and oxygen with a partial pressure of 2.5.1 O ⁇ Pa oxygen.
  • the sulphate content of the oxide thus treated is 0.25%.

Abstract

The invention concerns a method for treating a composition based on cerium oxide or a mixture of cerium oxide and zirconium oxide to increase said composition oxygen-storing capacity. Said method is characterised in that it consists in subjecting a composition containing at least one impurity such as carbonate, chloride, sulphate, oxalate or citrate, at least 0.1 % in content, to a thermal treatment at a temperature of at least 600 °C, in the presence of oxygen.

Description

PROCEDE DE TRAITEMENT D'UNE COMPOSITION A BASE D'OXYDE DE CERIUM PROCESS FOR TREATING A COMPOSITION BASED ON CERIUM OXIDE
POUR AUGMENTER LA CAPACITE DE STOCKAGETO INCREASE THE STORAGE CAPACITY
DE LOXYGENE DE CETTE COMPOSITIONLOXYGEN FROM THIS COMPOSITION
RHODIA CHIMIERHODIA CHEMISTRY
La présente invention concerne un procédé de traitement d'une composition à base d'oxyde de cérium ou d'un mélange d'oxyde de cérium et d'oxyde de zirconium, en vue d'augmenter la capacité de stockage de l'oxygène de cette composition.The present invention relates to a process for treating a composition based on cerium oxide or a mixture of cerium oxide and zirconium oxide, in order to increase the oxygen storage capacity of this composition.
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 des oxydes d'azote également présents dans ces gaz (catalyseurs "trois voies"). Les compositions à base d'oxyde de cérium ou d'un mélange d'oxyde de cérium et d'oxyde de zirconium apparaissent aujourd'hui comme particulièrement importantes et intéressantes pour ce type de catalyseurs.At the present time, so-called multifunctional catalysts are used for the treatment of exhaust gases from internal combustion engines (automotive post-combustion catalysis). Multifunctional means the catalysts capable of carrying out not only the oxidation in particular of carbon monoxide and of the hydrocarbons present in the exhaust gases but also the reduction of the nitrogen oxides also present in these gases (catalysts "three ways "). Compositions based on cerium oxide or on a mixture of cerium oxide and zirconium oxide appear today to be particularly important and advantageous for this type of catalyst.
~ Pour être efficaces, ces catalyseurs doivent assurer un pouvoir tampon vis à vis des variations de la teneur en oxygène du mélange gazeux à traiter. Ce pouvoir tampon est évalué par la capacité à stocker l'oxygène en milieu oxydant et à le restituer en milieu réducteur. Pouvoir améliorer cette capacité de stockage de l'oxygène présente donc un intérêt certain pour les catalyseurs de ce type. ~ To be effective, these catalysts must provide buffering power against variations in the oxygen content of the gas mixture to be treated. This buffering capacity is evaluated by the capacity to store oxygen in an oxidizing medium and to restore it in a reducing medium. Being able to improve this oxygen storage capacity therefore presents a certain interest for catalysts of this type.
L'objet de l'invention est un procédé qui permet d'obtenir une telle amélioration à partir de certaines compositions catalytiques.The object of the invention is a process which makes it possible to obtain such an improvement from certain catalytic compositions.
Dans ce but, le procédé selon l'invention de traitement d'une composition à base d'oxyde de cérium ou d'un mélange d'oxyde de cérium et d'oxyde de zirconium est caractérisé en ce qu'on soumet à un traitement thermique à une température d'au moins 600°C, en présence d'oxygène, une composition qui présente au moins une impureté de type carbonate, chlorure, sulfate, oxalate ou citrate, dans une teneur d'au moins 0,1% en poids exprimée en anion d'impureté par rapport à l'ensemble de la composition. 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.For this purpose, the method according to the invention for treating a composition based on cerium oxide or on a mixture of cerium oxide and zirconium oxide is characterized in that it is subjected to a treatment thermal at a temperature of at least 600 ° C., in the presence of oxygen, a composition which has at least one impurity of the carbonate, chloride, sulfate, oxalate or citrate type, in a content of at least 0.1% weight expressed as anion of impurity relative to the whole of the composition. Other characteristics, details and advantages of the invention will appear even more completely on reading the description which follows, as well as various concrete but nonlimiting examples intended to illustrate it.
Les compositions auxquelles s'applique le procédé de l'invention sont celles à base d'oxyde de cérium seul, ou d'un mélange d'oxyde de cérium et d'oxyde de 2 zirconium. On utilisera de préférence des compositions bien adaptées à l'application en catalyse, c'est à dire des compositions à surface spécifique suffisante. Dans le cas des compositions à base de cérium et de zirconium, celles-ci peuvent répondre notamment à la formule globale Ce-|.xZrxθ2 dans laquelle x vérifie la relation 0<x≤0,95. Plus particulièrement, x peut vérifier la relation 0,1<x<0,6 et, encore plus particulièrement, 0,2<x<0,5.The compositions to which the process of the invention applies are those based on cerium oxide alone, or on a mixture of cerium oxide and 2 zirconium. Preferably, compositions well suited to the application in catalysis will be used, that is to say compositions with a sufficient specific surface. In the case of cerium and zirconium-based compositions, these can correspond in particular to the overall formula Ce- |. x Zr x θ2 in which x satisfies the relation 0 <x≤0.95. More particularly, x can verify the relation 0.1 <x <0.6 and, even more particularly, 0.2 <x <0.5.
Ces compositions se préparent d'une manière connue par exemple par précipitation à partir de sels de cérium et de zirconium.These compositions are prepared in a known manner, for example by precipitation from cerium and zirconium salts.
Le procédé de l'invention s'applique aux compositions qui présentent une certaine teneur en impuretés. Ces impuretés peuvent être des carbonates, des chlorures, des sulfates, des oxalates ou des citrates ou encore des mélanges de ceux-ci. Ces impuretés proviennent généralement des précurseurs d'oxydes de cérium et de zirconium utilisés dans la préparation des compositions. La teneur en impureté est d'au moins 0J %. Cette teneur est exprimée, ici et pour l'ensemble de la description, en % en poids d'anion d'impureté par rapport à l'ensemble de la composition. Cette teneur peut être plus particulièrement d'au moins 0,3% et encore plus particulièrement d'au moins 1%.The process of the invention applies to compositions which have a certain content of impurities. These impurities can be carbonates, chlorides, sulfates, oxalates or citrates or mixtures of these. These impurities generally come from the precursors of cerium and zirconium oxides used in the preparation of the compositions. The impurity content is at least 0J%. This content is expressed, here and for the whole of the description, in% by weight of impurity anion relative to the whole of the composition. This content can more particularly be at least 0.3% and even more particularly at least 1%.
En outre, la composition à base d'oxyde de cérium ou d'un mélange d'oxyde de cérium et d'oxyde de zirconium, et susceptible d'être traitée par le procédé de l'invention, peut comprendre un additif, notamment en vue d'améliorer la stabilité de la surface spécifique. Cet additif peut être choisi, seul ou en mélange, parmi les terres rares; les alcalino-terreux; l'aluminium; le molybdène; le scandium; le silicium; le gallium; le titane; le vanadium; le niobium; le tantale. Par terre rare on entend les éléments du groupe constitué par l'yttrium et les éléments de la classification périodique de numéro atomique compris inclusivement entre 57 et 71. Comme terres rares, on peut mentionner notamment l'yttrium, le lanthane, le néodyme et le praséodyme. Le traitement thermique de l'invention est fait en présence d'oxygène. L'atmosphère dans laquelle est mis en oeuvre le procédé de l'invention peut être soit de l'oxygène pur, soit de l'oxygène dans un autre gaz qui peut être un gaz inerte, l'azote de préférence. Enfin, on peut aussi effectuer le traitement dans l'air, cet air pouvant être plus ou moins appauvri en oxygène. La pression partielle en oxygène peut varier dans une large gamme. Elle est habituellement comprise entre 10^Pa et 2,1.10^Pa. Elle peut être d'au plus 104Pa et plus particulièrement comprise entre 2.1θ3pa et 104Pa. On notera que le traitement peut aussi se faire dans une atmosphère contenant de l'eau, par exemple à une pression partielle d'eau d'au moins 103Pa.In addition, the composition based on cerium oxide or on a mixture of cerium oxide and zirconium oxide, and capable of being treated by the process of the invention, can comprise an additive, in particular by to improve the stability of the specific surface. This additive can be chosen, alone or as a mixture, from rare earths; alkaline earths; aluminum; molybdenum; scandium; silicon; gallium; titanium; vanadium; niobium; tantalum. By rare earth is meant the elements of the group consisting of yttrium and the elements of the periodic classification with atomic number between 57 and 71 inclusive. As rare earths, mention may be made in particular of yttrium, lanthanum, neodymium and praseodymium. The heat treatment of the invention is done in the presence of oxygen. The atmosphere in which the process of the invention is carried out can be either pure oxygen or oxygen in another gas which can be an inert gas, preferably nitrogen. Finally, it is also possible to carry out the treatment in air, this air possibly being more or less depleted in oxygen. The partial oxygen pressure can vary over a wide range. It is usually between 10 ^ Pa and 2.1.10 ^ Pa. It can be at most 10 4 Pa and more particularly between 2.1θ3pa and 10 4 Pa. Note that the treatment can also be carried out in an atmosphere containing water, for example at a partial pressure of water d '' at least 10 3 Pa.
La température de traitement est d'au moins 600°C. Généralement, elle sera comprise entre 600°C et 900°C. Une élévation de la température augmente 3 généralement l'efficacité du traitement. Toutefois, une température trop élevée pourrait modifier les propriétés de la composition traitée et notamment avoir une influence défavorable sur sa surface spécifique. La température de traitement dépend aussi du type d'impureté présente dans la composition à traiter. Ainsi, dans les cas des impuretés nitrates ou carbonates, cette température peut être comprise entre 600°C et 750°C, plus particulièrement entre 650°C et 750°C. Dans le cas des sulfates, on se place de préférence à une température d'au moins 800°C, plus particulièrement d'au moins 850°C. En travaillant en présence d'eau, la température de traitement peut être abaissée. La durée du traitement peut varier dans de larges limites.The processing temperature is at least 600 ° C. Generally, it will be between 600 ° C and 900 ° C. A rise in temperature increases 3 generally the effectiveness of treatment. However, too high a temperature could modify the properties of the treated composition and in particular have an unfavorable influence on its specific surface. The treatment temperature also depends on the type of impurity present in the composition to be treated. Thus, in the case of nitrates or carbonates impurities, this temperature can be between 600 ° C and 750 ° C, more particularly between 650 ° C and 750 ° C. In the case of sulfates, it is preferably placed at a temperature of at least 800 ° C., more particularly of at least 850 ° C. By working in the presence of water, the treatment temperature can be lowered. The duration of treatment can vary within wide limits.
Selon un mode de réalisation particulier de l'invention, le traitement thermique est mis en oeuvre en observant des paliers lors de la montée en température de l'ambiante à la température à laquelle doit se dérouler le traitement. Le nombre de paliers peut être quelconque. Par exemple, pour une température de traitement de 850°C, on peut observer un palier à 100°C et à 300°C. La durée du palier peut être d'une heure environ. Il est aussi possible, dans le cas où des paliers sont effectués, d'effectuer un traitement sous vide de la composition, à l'issue d'au moins un palier et avant de continuer la montée en température. Ce traitement sous vide se fait à la température du palier. La durée de ce traitement sous vide peut être d'une heure environ. A l'issue du traitement sous vide, on continue le traitement sous oxygène en remontant la température.According to a particular embodiment of the invention, the heat treatment is implemented by observing stages during the rise in temperature of the ambient to the temperature at which the treatment must take place. The number of steps can be arbitrary. For example, for a processing temperature of 850 ° C, one can observe a plateau at 100 ° C and 300 ° C. The duration of the landing can be approximately one hour. It is also possible, in the case where stages are carried out, to carry out a treatment under vacuum of the composition, at the end of at least one stage and before continuing the rise in temperature. This vacuum treatment is done at bearing temperature. The duration of this vacuum treatment can be approximately one hour. After the vacuum treatment, the oxygen treatment is continued by increasing the temperature.
On observe à l'issue du traitement qui vient d'être décrit que les compositions obtenues présentent une capacité de stockage de l'oxygène améliorée par rapport aux compositions non traitées. Ceci les rend particulièrement adaptées au traitement des gaz d'échappement des moteurs à combustion interne. Des exemples vont maintenant être donnés. Description du test permettant de quantifier le stockage de l'oxygène Le pouvoir tampon d'une composition vis-à-vis de Foxygène est évalué par sa capacité à stocker l'oxygène en milieu oxydant et à le restituer en milieu réducteur. Le test évalue la capacité de la composition à successivement oxyder des quantités déterminées de monoxyde de carbone d'oxygène et à consommer des quantités déterminées d'oxygène pour réoxyder la composition. La méthode employée est dite alternée.It is observed at the end of the treatment which has just been described that the compositions obtained have an improved oxygen storage capacity compared to the untreated compositions. This makes them particularly suitable for the treatment of exhaust gases from internal combustion engines. Examples will now be given. Description of the test making it possible to quantify the storage of oxygen The buffering capacity of a composition with respect to oxygen is evaluated by its capacity to store oxygen in an oxidizing medium and to restore it in a reducing medium. The test evaluates the capacity of the composition to successively oxidize determined quantities of carbon monoxide of oxygen and to consume determined quantities of oxygen to reoxidize the composition. The method used is said to be alternate.
Le gaz porteur est de l'hélium pur à un débit de 10/h. Les injections se font par l'intermédiaire de boucle contenant 16ml de gaz. Les quantités de CO sont apportées en utilisant un mélange gazeux contenant 5% de CO dilué dans l'hélium tandis que les quantités d'02 sont apportées à partir d'un mélange gazeux contenant 2,5% d'02 dilué dans l'hélium. L'analyse des gaz est effectuée par chromatographie à l'aide d'un détecteur de conductivité thermique.The carrier gas is pure helium at a flow rate of 10 / h. The injections are made via a loop containing 16ml of gas. The quantities of CO are supplied using a gaseous mixture containing 5% of CO diluted in helium while the quantities of O 2 are supplied from a gaseous mixture containing 2.5% of diluted O 2 in helium. The gas analysis is carried out by chromatography using a thermal conductivity detector.
La quantité d'oxygène consommée permet de déterminer la capacité de stockage d'oxygène (OSC). La valeur caractéristique du pouvoir de stockage d'oxygène est exprimée en ml d'oxygène (dans les conditions normales de température et de pression) par gramme de produit introduit et elle est mesurée à 400°C.The amount of oxygen consumed determines the oxygen storage capacity (OSC). The characteristic value of the oxygen storage capacity is expressed in ml of oxygen (under normal temperature and pressure conditions) per gram of product introduced and it is measured at 400 ° C.
FXEMPLE COMPARATIF 1FX COMPARATIVE EXAMPLE 1
Cet exemple concerne la préparation d'un oxyde mixte de formule Ce0,62Z o,38θ2-This example relates to the preparation of a mixed oxide of formula Ce 0 , 62Z o, 38θ2-
Dans les proportions stoechiométriques requises pour l'obtention de l'oxyde mixte ci-dessus, on mélange une solution de nitrate cérique et une solution de sulfate de zirconyle. Cette dernière a été obtenue par attaque d'un carbonate à l'aide d'acide sulfurique concentré. La concentration de ce mélange (exprimée en oxyde des différents éléments) est ajustée à 80 g/l. Ce mélange est ensuite porté à 150°C pendant 4 heures.In the stoichiometric proportions required for obtaining the above mixed oxide, a solution of ceric nitrate and a solution of zirconyl sulfate are mixed. The latter was obtained by attacking a carbonate using concentrated sulfuric acid. The concentration of this mixture (expressed as the oxide of the various elements) is adjusted to 80 g / l. This mixture is then brought to 150 ° C for 4 hours.
Une solution d'ammoniaque est ensuite ajoutée au milieu réactionnel de telle sorte que le pH soit supérieur à 8,5. Le milieu réactionnel ainsi obtenu est porté à ébullition pendant 2 heures. Après décantation puis soutirage, on remet en suspension le produit solide et le milieu ainsi obtenu est traité pendant 1 heure à 100°C. Le produit est ensuite filtré puis calciné sous air à la température de 400°C pendant 3 heures. La teneur en sulfate du produit ainsi obtenu est de 2,1% en poids de SO^".An ammonia solution is then added to the reaction medium so that the pH is greater than 8.5. The reaction medium thus obtained is brought to boiling for 2 hours. After decantation then racking, the solid product is resuspended and the medium thus obtained is treated for 1 hour at 100 ° C. The product is then filtered and calcined in air at a temperature of 400 ° C for 3 hours. The sulfate content of the product thus obtained is 2.1% by weight of SO 2 " .
EXEMPLE 2 SELON L'INVENTIONEXAMPLE 2 ACCORDING TO THE INVENTION
On prépare un oxyde mixte de formule identique à celle de l'exemple 1.A mixed oxide of formula identical to that of Example 1 is prepared.
On procède comme à l'exemple 1 , à l'exception de l'étape finale de calcination que l'on réalise à la température de 850°C pendant 5 heures dans une atmosphère d'azote et d'oxygène avec une pression partielle en oxygène de 2,5.1 O^Pa. La teneur en sulfate de l'oxyde ainsi traité est de 0,25%.The procedure is as in Example 1, except for the final calcination step which is carried out at the temperature of 850 ° C. for 5 hours in an atmosphere of nitrogen and oxygen with a partial pressure of 2.5.1 O ^ Pa oxygen. The sulphate content of the oxide thus treated is 0.25%.
Le tableau ci-dessous regroupe les caractéristiques des produits des exemples.The table below groups together the characteristics of the products in the examples.
Exemple Surface spécifique SO42- OSC 400°C en m2/q % en poids ml 0?/qExample Specific surface SO4 2 - OSC 400 ° C in m 2 / q% by weight ml 0? / Q
1 87 2,1 0.1
Figure imgf000006_0001
2 40 0,25 1,9 1 87 2.1 0.1
Figure imgf000006_0001
2 40 0.25 1.9

Claims

5 5
REVENDICATIONS
1- Procédé de traitement d'une composition à base d'oxyde de cérium ou d'un mélange d'oxyde de cérium et d'oxyde de zirconium, en vue d'augmenter la capacité de stockage de l'oxygène de cette composition, caractérisé en ce qu'on soumet à un traitement thermique à une température d'au moins 600°C, en présence d'oxygène, une composition qui présente au moins une impureté de type carbonate, chlorure, sulfate, oxalate ou citrate, dans une teneur d'au moins 0,1% en poids exprimée en anion d'impureté par rapport à l'ensemble de la composition.1- Process for treating a composition based on cerium oxide or on a mixture of cerium oxide and zirconium oxide, with a view to increasing the oxygen storage capacity of this composition, characterized in that it is subjected to a heat treatment at a temperature of at least 600 ° C, in the presence of oxygen, a composition which has at least one impurity of the carbonate, chloride, sulfate, oxalate or citrate type, in a content of at least 0.1% by weight expressed as anion of impurity relative to the whole of the composition.
2- Procédé selon la revendication 1 , caractérisé en ce qu'on soumet à un traitement thermique une composition qui présente au moins une impureté du type précité dans une teneur d'au moins 0,3% en poids.2- A method according to claim 1, characterized in that subjected to a heat treatment a composition which has at least one impurity of the above type in a content of at least 0.3% by weight.
3- Procédé selon la revendication 1 ou 2, caractérisé en ce qu'on soumet à un traitement thermique une composition qui présente au moins une impureté du type précité dans une teneur d'au moins 1% en poids.3- A method according to claim 1 or 2, characterized in that subjected to a heat treatment a composition which has at least one impurity of the above type in a content of at least 1% by weight.
4-Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on effectue le traitement dans une atmosphère d'oxygène pur ou d'oxygène et d'un gaz inerte.4-Method according to one of the preceding claims, characterized in that the treatment is carried out in an atmosphere of pure oxygen or oxygen and an inert gas.
5- Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on effectue le traitement dans une atmosphère dont la pression partielle en oxygène est comprise entre 103Pa et 2J J04Pa.5- Method according to one of the preceding claims, characterized in that the treatment is carried out in an atmosphere whose partial oxygen pressure is between 10 3 Pa and 2J J0 4 Pa.
6- Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on effectue le traitement dans une atmosphère contenant de l'eau.6- Method according to one of the preceding claims, characterized in that the treatment is carried out in an atmosphere containing water.
7- Procédé selon l'une des revendications précédentes, caractérisé en ce qu'on soumet à un traitement thermique une composition qui présente au moins une impureté du type sulfate à une température d'au moins 800°C. 7- Method according to one of the preceding claims, characterized in that subjected to a heat treatment a composition which has at least one impurity of the sulfate type at a temperature of at least 800 ° C.
PCT/FR1999/000334 1998-02-16 1999-02-15 Method for treating a cerium oxide based composition to increase said composition oxygen-storing capacity WO1999041009A1 (en)

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US7632769B2 (en) 2004-07-26 2009-12-15 Hiroshi Okamoto Zirconia porous body and manufacturing method thereof

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GB0224180D0 (en) * 2002-10-17 2002-11-27 Magnesium Elektron Ltd Improved oxygen storage component

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EP0153228A1 (en) * 1984-02-20 1985-08-28 Rhone-Poulenc Chimie Cerium dioxide with morphological characteristics, and process for its preparation
FR2701471A1 (en) * 1993-02-10 1994-08-19 Rhone Poulenc Chimie Process for the synthesis of compositions based on mixed oxides of zirconium and cerium, compositions thus obtained and uses thereof.
EP0628515A1 (en) * 1992-01-30 1994-12-14 Santoku Metal Industry Co., Ltd. Cerium and zirconium-containing compounds oxide and method for producing same
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EP0628515A1 (en) * 1992-01-30 1994-12-14 Santoku Metal Industry Co., Ltd. Cerium and zirconium-containing compounds oxide and method for producing same
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WO1997043214A1 (en) * 1996-05-15 1997-11-20 Rhodia Chimie Cerium oxide and zirconium oxide based composition, method of preparation and utilisation in catalysis

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7632769B2 (en) 2004-07-26 2009-12-15 Hiroshi Okamoto Zirconia porous body and manufacturing method thereof
US7642210B2 (en) 2004-07-26 2010-01-05 Daiichi Kigenso Kagaku Kogyo Co., Ltd. Zirconia porous body and manufacturing method thereof

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