COMPOSITION CONTAINING ZIRCONIUM OXIDES, OF CERIUM Of AT LEAST ANOTHER RARE EARTH, HAS SPECIFIC POROSITY, PROCEEDED OF PREPARATION AND USE IN CATALYSIS.

The present invention relates to a composition based on zirconium oxide, cerium oxide and at least one rare earth oxide other than cerium, to specific porosity, process for its preparation and its use in catalysis

At the present time is used for the treatment of exhaust gases of internal combustion engines (catalysis motor afterburning) said multifunctional catalysts. For multifunctional, is the catalysts capable of operating not only the oxidation in particular carbon monoxide and hydrocarbons present in the exhaust gas but also reduction in particular nitrogen oxides also present in these gases ("three-way" catalysts). The zirconium oxide and cerium oxide as two components appear today particularly important and attractive such catalyst.

Products of this type should have a porosity adapted to their use. Therefore, they should have a sufficiently large pore volume and also have pores large enough to allow a good diffusion of gas.

However, such products must also have pores small sizes, since they are the pores that aid in providing the products to a specific surface area sufficiently high to be usable catalysis.

It is therefore of interest to find a good compromise between a large area, provided by the small pore sizes and gas diffusion provided by the large pore sizes.

To provide a product which has a pore volume large pores and both large and small.

For this purpose, the composition of the invention is based on zirconium oxide, cerium oxide and yttrium oxide or it is based on zirconium oxide, cerium oxide and of at least two oxides of two rare earths other than cerium, in a proportion by mass of zirconium-oxide of at least 20% and cerium oxide of at most 70%, and it is characterized in that it has, after calcination at a temperature of 900 °C during 4 hours, two populations of pores having the respective diameters are centered, for the first, about a value between 20 and 40 nm and, for the second, about a value between 80 nm and 200 nm.

Other features, details and advantages of the invention will appear even more completely reading the description which will follow, as well as various concrete but non-limiting examples illustrate for.

For following the description, the above specific surface area, the B.E.T. specific surface area determined by nitrogen adsorption according to ASTM D 3663-78 established from the method described in the periodical BRUNAUER EMMETTTELLER "The Journal of the American Chemical Society, 60, 309 (1938)".

For the present disclosure is understood as meaning the elements of the rare earth group consisting of yttrium and the elements of the periodic system of atomic numbers inclusively between 57 and 71.

Furthermore, the calcinations for a temperature and time data correspond, unless otherwise indicated, to the calcinations in air at a temperature level on the indicated length of time.

The contents data oxide are by weight unless otherwise indicated. The cerium oxide is in the form of ceria, the oxides of the other rare earths as Ln₂ C > 3, Ln designates the rare earth, with the exception of the praseodymium expressed as PreOn.

It is clarified for the rest of the description that, unless otherwise indicated, in the value ranges which are data, the values at the terminals are included.

The compositions of the invention have first by the nature of their constituents.

The compositions of the invention are based on zirconium oxide, cerium oxide and, according to a first embodiment, an yttrium oxide. In a second embodiment, the compositions of the invention are also based on zirconium oxide and cerium oxide and they also comprise oxides of at least two other rare earths that are different from the cerium. The compositions of the invention may be based on three, four or, in another preferred embodiment, five-based oxides, i.e. in this case that the compositions contain three other rare earths different cerium.

The rare earths other than cerium may be more particularly selected from yttrium, lanthanum, neodymium, praseodymium or gadolinium. Include particularly those made of oxides of zirconium, cerium, yttrium, neodymium and lanthanum or zirconium oxides, cerium, yttrium, praseodymium and lanthanum.

The content of zirconium oxide is at least 20%. The concentration can be more particularly at least 25% or still more particularly at least 40%. More precisely, the content may be at least 45%, preferably at least 55%. The can be mentioned and a zirconium content which will be comprised between 40% and 80% and more particularly between 50% and 75%.

The cerium oxide content is at most 70% and more particularly at most 50% and even more particularly at most 45% or 40%. The minimum amount of cerium is not critical. Preferably however it is at least 0.1% and more particularly at least 1% and still more particularly at least 5%. It can be between 5% and 45% and in particular between 10% and 40%.

The oxide content of yttrium oxide or more generally the set of rare earths other than cerium is generally at most 30%, more particularly at most 20% and at least 4%, preferably at least 5% and in particular at least 10%. It can be in particular between 10% and 30% and in particular between 10% and 25%.

In the case of compositions containing as little as yttrium oxide the values given above are same, but content of yttrium can be more particularly between 7% and 25%.

As is seen above, one of the main features of the compositions of the invention is their porosity.

Therefore, the compositions of the invention have two populations of distinct pores well and which are centred about the data values higher.

The herein and for the set of the description that the indicated porosities are measured by mercury intrusion porosimetry in accordance with ASTM D 4284-83 (Standard method for provided pore volume distribution of catalysts by mercury intrusion porosimetry).

The porosity measurement given above can be used to establish porogrammes known manner of giving the pore volume based on the size of the pores (V = f (d), V is the pore volume and d is the diameter of the pores). From this porogramme it is possible to obtain, always be known, a curve (C) giving the derivative of V based on d. This curve may have peaks according to the diameter of the pores.

According to the invention is understood as meaning "population of pores having diameters centered about a given value", the presence in the curve (C) of a peak having the maximum is at the given value. Furthermore, it should be noted that when it is indicated that the compositions of the present invention have one or two populations of pores not possible that there may be other populations of pores. In fact the pores which are considered as characteristics of the invention are mesopores or macropores i.e. pores of a diameter of at most 350 nm. In other words the compositions of the subject invention exhibit pores in the range of about 1 nm to about 350 nm.

Therefore, as indicated above, after calcination at a temperature of 900 °C during 4 hours the compositions have two populations of pores. The first population corresponds to pores whose diameters are centered on a value between 20 nm and 40 nm, in particular between 20 nm and 35 nm and more particularly between 20 and 30 nm and even more particularly about 25 nm. The second population corresponds to pores whose diameters are centered on a value between 80 nm and 200 nm, in particular between 80 nm and 150 nm and more particularly between 130 nm and 80 nm. This value can also be between 90 nm and 150 nm and more particularly between 110 nm and 90 nm, and even more particularly about 100 nm.

After calcination at higher temperatures, the porosity of the compositions of the invention changes. Therefore, after calcination at 1000 °C 4 hours they have a population of pores, the diameter of which is centered on a value between 30 nm and 40 nm and more specifically around 35 nm. At this temperature, the compositions of the subject invention exhibit pores in the range of about 1 nm to about 300 nm.

Furthermore after calcination at 1100 °C 4 hours, they have a population of pores, the diameter of which is centered on a value between 30 nm 70 nm and more specifically around 50 nm. At this temperature, the compositions of the subject invention exhibit pores in the range of about 1 nm to about 300 nm.

The presence of a population of pores centered on the values described above provides balance of the thermal stability of the specific surface area and the gas diffusion.

The compositions of the invention comprise a total pore volume of at least 1.5 ml Hg/g, this pore volume being measured compositions having calcined at a temperature of 900 °C during 4 hours. The total pore volume may be in particular of at least 1.6 ml Hg/g, more particularly at least 1.7 ml and still more particularly at least 1.8 ml Hg/g. In these same conditions of calcining the pore volume of at least about 2.2 ml Hg/g can be obtained.

Compositions The total pore volume measured after calcination at 1000 °C 4 hours is at least 1.5 ml/g of Hg and Hg at least 0.9 ml/g to 1100 °C 4 hours. A 1000 °C of pore volume to at least about 1.9 ml Hg/g can be obtained and to 1100 °C to at least about 1.3 ml Hg/g.

After calcination at 1000 °C 4 hours the compositions of the invention are in the form of two different crystallographic phases cubic in nature.

The crystallographic structures are highlighted by the ray diffraction patterns of the compositions of the invention. RX These same patterns can be determined by the formula of Scherrer a crystallite size measured on peaks more intense at most 8 nm.

The compositions of the invention have a high specific surface area in particular as a result of their specific porosity.

Therefore, after calcination at 1100 °C 4 hours, they have for the compositions with a zirconium oxide content of at least 45% a specific surface area of at least 25 m² / g, more particularly at least 27 m² / g, especially in the case where the amount of rare earth element other than cerium is higher. Area values of at least 33 m² / g can be obtained.

After calcination at 1150 °C 10 hours they may have a specific surface area of at least 7 m² / g, preferably at least 10 m² / g. Area values of at least 18 m² / g can be obtained.

After calcination at 1200 °C 10 hours the compositions of the invention may exhibit a specific surface area of at least 2 m² / g, preferably at least 4 m² / g and still more particularly at least 6 m² / g. Area values up to about 12 m² / g can be obtained.

Probably also due to their specific porosity, compositions of the invention have the advantage of a storage capacity and delivery oxygen (OSC) is improved with respect to products which do not have two populations of pores. This improvement will appear to reading the examples at the end of the description.

The method for preparing compositions of the invention will now be described.

The method comprises the following steps:

-(a) forming a mixture comprising either compounds zirconium and cerium is only these compounds with one or more rare earth compounds other than cerium in an amount of the latter compounds that is less than the amount necessary to obtain the desired composition,

-(b) are brought into contact, under stirring, said mixture with a basic compound;

-(c) are brought into contact, under stirring, the mixture obtained in the preceding step with either the compound or compounds of rare earths other than cerium if the one or more compounds were not present in step (a) is the remaining amount necessary said compound or compounds, the stirring energy used in step (c) being less than that used in step (b);

-(d) is heated in aqueous medium said precipitate;

-(e) is added to the precipitate obtained in the previous step an additive selected from anionic surfactants, nonionic surfactants, polyethylene glycols, carboxylic acids and their salts and ethoxylates type surfactants carboxymethylated fatty alcohols;

-(f) the resulting precipitate is calcined.

The first step (a) of the method is provided for preparing a mixture of some of the compounds of the components of the composition sought to prepare. The mixture is effected generally in a liquid medium is preferably water.

This step (a) can be carried out according to two variants.

In the case of the first variant, which is a preferred embodiment, the mixture formed in step (a) includes, the components of the composition, i.e. zirconium, yttrium or cerium and other rare earths, that the compounds of zirconium and cerium.

In the case of the second variant the mixture formed in step (a) comprises, in addition to compounds zirconium and cerium, the compound or compounds of other rare earths different cerium but in an amount that is less than the total amount required stoichiometric of the compound other rare earths to the obtaining of the desired composition.

This amount can be especially at most equal to half of the total amount.

Therefore, for example in the case of compositions made of oxides of zirconium, cerium and yttrium, according to the second embodiment the yttrium compound will be present in step (a) in an amount less than the total amount stoichiometrically necessary to the composition. The same applies to compositions based on zirconium oxide, cerium and at least two other rare earths, the amount of the compounds of these other rare earths in step (a) is less than the total amount required stoichiometric.

It should be noted that the second embodiment must to be taken as covering the case, for the compositions made of oxides of zirconium, cerium and at least two other rare earths, wherein in step (a) the amount total required compound at least one rare earth is present from the step and only for at least one of the other remaining rare earths that the amount of the compound of the other rare earth is less than the amount necessary. It is also possible that the compound of the other rare earth is absent to the step (a).

The compounds are preferably soluble compounds. The can be especially salts of zirconium, cerium and rare earth. Such compounds can be chosen from nitrates, sulfates, acetates, chlorides, ceriammoniacal nitrate.

Exemplary, can be include zirconium sulfate, zirconyl nitrate or zirconyl chloride. The zirconyl nitrate is used most generally. Also include in particular the salts of cerium IV such as nitrate or ceriammoniacal nitrate for example, useful herein particularly well. Preferably, ceric nitrate is used. It is advantageous to use salts of purity of at least 99.5% and more particularly at least 99.9%. An aqueous solution of ceric nitrate can, for example, be obtained by reaction of the nitric acid on hydrated cerium oxide prepared in a conventional manner by reacting cerous a solution of a salt, for example the cerous nitrate, and a solution of ammonia in the presence of hydrogen peroxide. May also, preferably, a solution of ceric nitrate obtained according to the process of electrolytic oxidation of a solution of cerous nitrate as described in the document FR-A 2 570,087, and which is herein a raw material of interest.

It should be noted herein that the aqueous solutions of cerium salts and zirconyl salts may have some initial free acidity can be adjusted by the addition of a base or an acid. However, it is as much possible to implement an initial solution ceria zirconia actually having a certain free acidity as mentioned above, that solutions which will have been previously neutralized more or less thrust. Neutralization may be by adding a basic compound to the aforementioned mixture so as to limit this acidity. The basic compound may be, for example, a solution of ammonia or alkali hydroxides (sodium, potassium, ...), but preferably a solution of ammonia.

It should be noted that when the starting mixture contains cerium as III, it is preferable to it is used in the course of the process an oxidizing agent, for example hydrogen peroxide. The oxidizing agent can be used by being added to the reaction medium in step (a), in step (b) or at the start of step (c).

Finally, it is also possible to use ground as the starting compound, zirconium or cerium. Ground is designated For any system consisting of fine solid particles of colloidal size, i.e. dimensions of between about 1 nm to about 200 nm, comprised of zirconium compound or the compound is generally a cerium oxide and/or a hydrated oxide of zirconium or cerium, suspended in an aqueous liquid phase.

The mixture can be any of compounds obtained from either initially solid state will introduce that is subsequently in a stock such as water, or directly from solutions or suspensions of these compounds and then mixing, in any order, said solutions or suspensions.

In the second step (b) of the method, said mixture is placed in contact with a basic compound to react them. Can be used as base or basic compound products hydroxide. Include hydroxides of alkali metal or alkaline earth metal. It is also possible to use secondary amines, tertiary or quaternary. However, amines and ammonia may be preferred in that they reduce the risk of pollution by the alkali or alkaline earth cations. Urea may also be mentioned.

The basic compound can more particularly be used in the form of a solution. Finally, it can be used with a stoichiometric excess to ensure optimal precipitation.

The presence is carried out while stirring. It can be performed in any desired manner, for example through the addition of a previously formed mixture of the compounds of the above in the basic compound in the form of a solution.

The next step (c) of the method consists in introducing the medium from the preceding step (b) with the compounds of the rare earths other than cerium. In the case of the aforementioned first embodiment wherein the starting mixture formed in step (a) comprises, as constituent elements of the composition, that the compounds of zirconium and cerium, these compounds are so introduced for the first time in the method and in the total amount of the required stoichiometric other rare earths. In the case of the second embodiment in which the mixture formed in step (a) already comprises compounds of other rare earths different cerium it is therefore of the remaining amount required of these compounds or, optionally, of the necessary quantity of the compound of a rare earth whether the compound were not present in step (a).

The presence may be performed in any desired manner, for example through the addition of a previously formed mixture of the compounds of rare earths other than cerium in the mixture obtained from step

(b). It is also under agitation but under conditions such that the stirring energy used during this step (c) is less than that used in step (b). Specifically the energy in the step (c) is lower by at least 20% than that of the step (b) and it may be more preferably less than 40%, and even more particularly 50% thereof.

Are obtained at the end of step (c) a precipitate suspended in the reaction medium.

The next step (d) of the method is the step of heating the precipitate under the medium.

The Heating can be formed directly on the reaction medium obtained at the end of step (c) or on a suspension obtained after precipitate is separated from the reaction medium, washing and returned to water of the precipitate. The temperature at which the medium is heated is at least 100 °C and still more particularly at least 130 °C. It can be for example between 100 °C and 160 °C. The heating may be conducted by introducing the liquid medium in an enclosed chamber (closed reactor autoclave type). In temperature conditions given above, and in an aqueous medium, may be specify, illustrative, that the pressure in the tank may vary from greater than 1 Bar (10⁵ Pa) and 165 Bar (1.65. 10⁷ Pa), preferably between 5 Bar (10 5.⁵ Pa) and 165 Bar (1.65. 10⁷ Pa). May also be the heating in an open reactor for the at near 100 °C.

The heating can be carried out either in air, or under an inert gas atmosphere, preferably nitrogen.

The duration of the heating can vary within wide limits, for example between 1 and 48 hours, preferably between 2 and 24 hours. Also, the temperature rise occurs at a speed that is not critical, and can be reach the reaction temperature fixed by heating the medium for example between 30 minutes and 4 hours, these values being exemplary quite indicative.

It is possible to more heaters. Therefore, re suspension in water, the precipitate obtained after the heating step and optionally washing and then perform another heating the mixture thus obtained. The other heating is in the same conditions as those which have been described for the first.

The next step (e) of the method comprises adding to the precipitate resulting from the previous step an additive which is selected from anionic surfactants, nonionic surfactants, polyethylene glycols and carboxylic acids and their salts and ethoxylates type surfactants carboxymethylated fatty alcohols.

For the additive can be referring to the teaching of the request WO-98/45212 and using the surfactants disclosed herein.

The can be mentioned as surfactants the anionic type éthoxycarboxylates , ethoxylated fatty acids, sarcosinates, phosphate esters, the sulfates as alcohol sulfate ether sulfates and alcohol ethoxylates sulfated alkanolamide, sulfonates such as sulfosuccinates, alkyl the alkyl benzene or naphthalene sulfonates.

As nonionic surfactants there can be mentioned the acetylenic surfactants, alcohol ethoxylate, alkanolamides, amine oxides, ethoxylated alkanolamides, ethoxylated amines long chain, the copolymers ethylene oxide/propylene oxide, sorbiatan derivatives, ethylene glycol, propylene glycol, glycerol, polyglyceryle the esters and ethoxylated derivatives thereof, alkylamines, the alkylimidazoline, oils and ethoxylated alkylphenol ethoxylate. Include in particular the products sold under the brand IGEPAL ®, DOWANOL ®, RHODAMOX and ALKAMIDE ®®.

For carboxylic acids, for monoou aliphatic dicarboxylic acids and more particularly saturated acids. Can be used more particularly fatty acids and saturated fatty acids. The particular, include formic, acetic, propionic, butyric, isobutyric, valeric, caproic, caprylic, capric, lauric, myristic, palmitic. Since dicarboxylic acids, there can be mentioned oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic and sebacic.

The salts of the carboxylic acids may also be used, in particular ammonia salts.

For example, include more particularly lauric acid and ammonium laurate.

Finally, it is possible to use a surfactant which is selected from those of the type ethoxylates carboxymethylated fatty alcohols.

For product such as carboxymethylated fatty alcohol ethoxylates is the products made of ethoxylated or propoxylated fatty alcohols having chain end a group CH2-COOH.

The products may correspond to formula:

Ri-0-(CR2R3-CR₄ R5-0) N-CH C00H 2-

wherein Ri denotes a carbon chain, saturated or unsaturated, whose length is generally at most 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R₄ and R5 may be the same and be hydrogen or R2 may be CH3 and R3, R₄ and R5 are hydrogen; n is a non-zero whole number up to 50 and more particularly between 5 and 15, these values being included. A a surfactant may be comprised of a mixture of products of the above formula for which Ri may be saturated or unsaturated and respectively products having both groups-CH 2-CH2- Oet -C (CH3)-CH2-0-.

The addition of the surfactant may either of two ways. It can be added directly into the suspension of a precipitate end of the previous step (d) heating. It can also be added to the solid precipitate after separation thereof by any known means of the medium in which the heating has occurred.

The amount of surfactant used, expressed as percentage by weight of the additive relative to the weight of the composition calculated oxide, is generally between 5% and 100% more particularly between 15% and 60%.

In another advantageous alternative of the invention, before implementing it the last step of the method (calcination step), rinsing is performed after the precipitate separated from the medium in which it was suspended. The cleaning may be water, preferably with water at basic pH, e.g. ammonia water.

In a last step of the process according to the invention, the recovered precipitate is then calcined. The calcination makes it possible to develop the crystallinity of the formed product and it can be adjusted and/or selected as a function of the temperature of subsequent use reserved for the composition according to the invention, and by taking account of the fact that the surface area of the product is set lower as the calcination temperature implementation is higher. Such calcination is generally carried out in the air, but a calcination driven for example in inert gas or in a controlled atmosphere (oxidizing or reducing) is obviously not excluded.

In practice, generally is limited the calcination temperature to a range of values between 500 and 900 °C more particularly between 700 °C and 800 °C.

The compositions of the invention as described above or those obtained by the preparation process described previously are available in the form of powders but may be optionally shaped to take the form of granules, beads, cylinders or honeycombs of varying sizes.

These compositions can be used with any material usually employed in the field of the catalyst system, i.e. in particular thermally inert materials. This material can be selected from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinels, zeolites, silicates, the crystalline silicoaluminium phosphate, the crystalline aluminium phosphate.

The compositions may also be used in catalytic systems comprising a coating (wash coat) with catalytic properties and them with a material of the type mentioned above, the coating being deposited on a substrate such as metal monolith, e.g. FerCralloy , or ceramic, for example cordierite, silicon carbide, alumina titanate or mullite.

The coating is obtained by mixing the composition with the material so as to form a suspension which can be then deposited on the substrate.

The catalyst systems and more particularly the compositions of the invention may find a wide range of applications.

They are particularly well suited for, and suitable for use in the catalysis of various reactions, such as, for example, the dehydration, the hydrodesulfurization, hydrodenitrification, the desulfurization, hydrodesulfurization, the dehydrohalogenation, reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, disproportionation, the oxychlorination, the dehydrocyclization of hydrocarbons or other organic compounds, oxidation reactions and/or reducing, the Claus reaction, the treatment of exhaust gases of internal combustion engines, the demetallating, methanation, the shift conversion, the catalytic oxidation of soot emitted from internal combustion engines such as diesel engines or gasoline lean.

Catalyst systems and compositions of the invention can also be used as NOx traps or to facilitate reduction of NOx even in an oxidizing medium.

In the case of these uses in catalysis, the compositions of the invention are provided in combination with precious metals, and they act as support for these metals. The nature of these metals and the techniques of incorporating them in the support compositions are well known to those skilled in the art. For example, the metals can be platinum, rhodium, palladium or iridium, including by impregnating be incorporated into the compositions.

Among the uses mentioned, the treatment of exhaust gases of internal combustion engines (catalysis automobile post combustion) is particularly useful.

Therefore, the invention also relates to a method for treating exhaust gases of internal combustion engines which is characterized in that there is used as catalyst a catalyst system as described above or a composition according to the invention and as described above.

Examples will now be given.

EXAMPLE 1

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, lanthanum, neodymium and yttrium in the following respective proportions in weight percent oxides: 75% is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other of nitrates of lanthanum, neodymium and yttrium. 0.39 In a first beaker I water is introduced with 0.25 I zirconium nitrate ([ Zr0₂ ] = 288 g/l and d = 1,433) and 0.04 I of cerium nitrate ([Ce0₂ ] = 246 g/l and d = 1.43). In a second beaker water are introduced 76.6 ml, 4.1 ml lanthanum nitrate ([The₂ 0₃ ] = 471 g/l and d = 1.69), 29.4 ml of yttrium nitrate ([Y₂ 0₃ ] = 261 g/l and d = 1,488) 9.9 ml and neodymium nitrate ([Nd₂ 0₃ ] = 484 g/l and d = 1,743).

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 500 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 250 rev/min.

The suspension of precipitate thus obtained is placed in a stainless steel autoclave equipped with a mixing unit. The temperature of the medium is heated to 150 °C during 2 hours under stirring.

Are added to the suspension thus obtained 33 grams lauric acid. The suspension is maintained under stirring for 1 hour.

The suspension is then filtered on Büchner, and then washed with water ammonia.

The resulting product is then calcined at 700 °C bearing during 4 hours.

EXAMPLE 2

This example relates to the preparation according to the second alternative of the first stage of the process of the invention of a composition identical to that of the example 1.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is of nitrates of cerium and zirconium with other rare earth elements 50% of the composition and the other being comprised of nitrates of the remaining amount (50%)of the same other elements. 0.41 In a first beaker I water is introduced with 0,275 I zirconium nitrate and 0,038 I of cerium nitrate, lanthanum nitrate 2.1 ml, 15.2 ml of yttrium nitrate and 5 ml of neodymium nitrate. In a second beaker 37.7 ml of water are introduced, lanthanum nitrate 2.1 ml, 15.2 ml of yttrium nitrate and 5 ml of neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 500 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 200 rev/min.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

EXAMPLE 3

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, lanthanum, neodymium and yttrium in the following respective proportions in weight percent oxides: 60%

-25%-2%-5%-8%.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other of nitrates of lanthanum, neodymium and yttrium. In a first beaker 0,382 I water is introduced with 0.2 I zirconium nitrate and 97.6 ml of cerium nitrate. In a second beaker water are introduced 76.6 ml, 4.1 ml lanthanum nitrate, 29.4 ml of yttrium nitrate and 9.9 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 500 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 250 rev/min.

The suspension of precipitate thus obtained is placed in a stainless steel autoclave equipped with a mixing unit. The temperature of the medium is heated to 150 °C during 1 hour with mixing.

Subsequently (addition of lauric acid, washing and calcination) as in the example 1.

EXAMPLE 4

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, lanthanum, neodymium and yttrium in the following respective proportions in weight percent oxides: 45%

-40%-2%-5%-8%.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other of nitrates of lanthanum, neodymium and yttrium. 0.37 I In a first beaker of water is introduced with 0.15 I zirconium nitrate and I 0,156 of cerium nitrate. In a second beaker water are introduced 76.6 ml, 4.1 ml lanthanum nitrate, 29.4 ml of yttrium nitrate and 9.9 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 450 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 200 rev/min.

The suspension of precipitate thus obtained is placed in a stainless steel autoclave equipped with a mixing unit. The temperature of the medium is heated to 125 °C during 1 hour with mixing.

Subsequently (addition of lauric acid, washing and calcination) as in the example 1.

EXAMPLE 5

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, lanthanum, neodymium and yttrium in the following respective proportions in weight percent oxides: 25%

-60%-2%-5%-8%.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other of nitrates of lanthanum, neodymium and yttrium. In a first beaker 0,362 I water is introduced with 83 ml zirconium nitrate and I 0,234 of cerium nitrate. In a second beaker water are introduced 76.6 ml, 4.1 ml lanthanum nitrate, 29.4 ml of yttrium nitrate and 9.9 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 350 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 190 rev/min.

The suspension of precipitate thus obtained is placed in a stainless steel autoclave equipped with a mixing unit. The temperature of the medium is heated to 150 °C during 30 minutes under stirring.

Subsequently (addition of lauric acid, washing and calcination) as in the example 1.

EXAMPLE 6

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, neodymium and yttrium in the following respective proportions in weight percent oxides: 75%-10% 12%-3%.

The solutions of nitrates of zirconium, cerium, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other nitrates of yttrium and neodymium. 0.39 In a first beaker I water is introduced with 0.25 I zirconium nitrate and I 0,039 of cerium nitrate. In a second beaker 69.9 ml of water are introduced, 44.1 ml of yttrium nitrate 6 ml and neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 500 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 250 rev/min.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

EXAMPLE 7

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, lanthanum, yttrium and praseodymium in the following respective proportions in weight percent oxides: 75%

-10%-3%-5%-7%.

The solutions of nitrates of zirconium, cerium, lanthanum and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other being comprised of lanthanum nitrate, yttrium, and praseodymium. 0.39 In a first beaker I water is introduced with 0,251 zirconium nitrate and I 0,039 of cerium nitrate. In a second beaker are lanthanum nitrate introduced 6.1 ml, 25.7 ml of yttrium nitrate, praseodymium nitrate 9.6 ml ([Pr₂ 05] 1500g and d=1,74 = / I) and water to obtain a solution at 120 g/l.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 400 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 250 rev/min.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

EXAMPLE 8

This example relates to the preparation according to the first alternative of the first stage of the process of the invention of a composition based on zirconium oxide, cerium, lanthanum, neodymium and yttrium in the following respective proportions in weight percent oxides: 65%

-10%-3.4%-13, 3%-8.3%.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other of nitrates of lanthanum, neodymium and yttrium. 0.34 In a first beaker I water is introduced with 0.22 I zirconium nitrate and I 0,039 of cerium nitrate. In a second beaker 0,127 L of water are introduced, 6.9 ml lanthanum nitrate, 0,049 I of yttrium nitrate and 16.5 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 45 minutes in the stirred reactor at a rate of 500 rpm, the second solution of nitrates is introduced in 15 minutes and the agitation is attached to 250 rev/min.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

This example relates to the preparation of a composition identical to that of the example 1 by a method in which the compounds of the rare earths other than cerium are made at different stages of the method, as in the previous examples, but with the same stirring energy in each of those steps, unlike these examples.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is of nitrates of cerium, zirconium, yttrium and lanthanum and neodymium nitrate the other. 0.41 In a first beaker I water is introduced with 0.25 I zirconium nitrate and 0.04 I of cerium nitrate, lanthanum nitrate 4.1 ml, 29.4 ml of yttrium nitrate. In a second beaker is introduced water 9.9 ml 50.6 ml and neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 50 minutes in the stirred reactor at a rate of 400 rpm, the second solution of nitrate is introduced in 10 minutes and the agitation is attached to 400 rpm.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

This example relates to the preparation of a composition based on zirconium oxide, cerium, neodymium and yttrium in the following respective proportions in weight percent oxides: 72%-10%-8%

-10%, according to a method in which the compounds of the rare earths other than cerium are made at different stages of the method, as in the examples 1 to 8, but with the same stirring energy in each of those steps, unlike these examples.

The solutions of nitrates of zirconium, cerium, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared previously two solutions of nitrates one is nitrate of cerium and zirconium and the other being comprised of yttrium nitrate and neodymium. In a first beaker 0,377 I water is introduced with 0.24 I zirconium nitrate and I 0,039 of cerium nitrate. In a second beaker are introduced 94.7 ml water, 29.4 ml of yttrium nitrate and 19.8 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the two solutions prepared previously. The first solution of nitrates is introduced in 40 minutes in the stirred reactor at a rate of 500 rpm, the second solution of nitrate is introduced in 20 minutes and the agitation is attached to 500 rpm.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

COMPARATIVE EXAMPLE 11

This example relates to the preparation of a composition identical to that of the example 2 but according to a method wherein the compounds of zirconium, cerium and other rare earths are made in the same step.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared beforehand, a nitrate solution of from 0.44 L of water, 0.27 I zirconium nitrate, 0,039 I of cerium nitrate, lanthanum nitrate 4.1 ml, 29.4 ml of yttrium nitrate and 9.9 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the nitrate solution prepared previously. This solution is introduced in 60 minutes in a stirred reactor at a rate of 450 rpm.

The suspension of precipitate thus obtained is placed in an autoclave and is then carried out (autoclaving, addition of lauric acid, washing and calcination) as in the example 1.

This example relates to the preparation of a composition identical to that of the example 3 but according to a method wherein the compounds of zirconium, cerium and other rare earths are made in the same step.

The solutions of nitrates of zirconium, cerium, lanthanum, neodymium and yttrium used in this example have the same characteristics as those used in the example 1.

Is prepared a solution of nitrates from 0,458 I water, 0.2 I zirconium nitrate, 97.6 ml of cerium nitrate, lanthanum nitrate 4.1 ml, 29.4 ml of yttrium nitrate and 9.9 ml neodymium nitrate.

In a reactor fitted with an agitation with inclined paddles, is introduced under stirring a solution of ammonia (12 mol/L) and then is completed with distilled water so as to obtain a total volume of 0.8 liter and a stoichiometric excess of 40% ammonia relative to the precipitating cations.

Is maintained under constant agitation the solution prepared previously. The solution of nitrates is introduced in 60minutes in the stirred reactor at a rate of 400 rpm.

The suspension of precipitate thus obtained is placed in a stainless steel autoclave equipped with a mixing unit. The temperature of the medium is heated to 150 °C during 1 hour with mixing.

Subsequently (addition of lauric acid, washing and calcination) as in the example 1.

Is given in the table 1 below for the composition of each of the previous examples the surfaces after calcination to the specific times and temperatures indicated. The calcinations to 900 °C and other temperature up to 1200 °C have been made on the products obtained at the end of the process described in the examples, i. e., products which have already undergone a first calcining at 700 °C.

Is given in the table 2 below for the composition of each of the previous examples the total pore volume and pore size. These features of porosities are those measured in compositions that have been calcined at 900 °C 4 hours. The values in the column "pore size" correspond to the diameters are centered around which the populations of pores, the indication of a single value indicating the presence of a single population and the indication of two values indicating the presence of two populations.

Table 2

Size Example total pore volume of pores

(hg ml/g) (nm)

1,1.8 25-100

2,1.6 25-100

3,1.74 25-100

4,1.8 30-100

Crystallographic structure

After calcination at 1000 °C 4 hours, the compositions of the examples 1 to 8 have two distinct crystallographic phases at least one of which is cubic and those of examples 9 to 12 a single phase.

EXAMPLE 13

This example illustrates the properties of OSC compositions of the invention (compositions of the examples 1 and 3) and comparative compositions (compositions of the example 9 comparative and according to the comparative example 12).

Are first impregnation to sec sample compositions such as obtained at the end of the process described in the examples mentioned in the preceding paragraph from a nitrate solution of rhodium in conditions such that the compositions have after impregnation a rhodium content of 0.1% (Rh content by mass of metal).

The impregnated compositions are then calcined at 500 °C 4 hours, in air. They are then an aging treatment at 1100 °C 6 hours in an atmosphere of 2% composition CO, 10% in H₂ 0 and the balance nitrogen and composition 2% in 0₂ , 10% in H₂ 0 and the balance nitrogen, the change of atmosphere which all 5 minutes.

30 mg of product are arranged in a reactor in which the temperature is regulated at 350 °C. Is injected into the reactor in amounts determined CO (5% in helium) and 0₂ (2.5% in helium) alternately, at a frequency of 1:00 z (one injection during 1 second) and at a flow rate of 200 cm³ / minute. Are analyzed at the outlet of the reactor and the content of CO 0₂ using a mass spectrometer.

The OSC is expressed in ml of 0₂ per second per gram and from the formula:

OSC (.g ml'¹ ' .s¹ ) = [ Λ (℮ 0) x dCO ] / (x 2 P)

wherein A (CO) represents the amount of CO converted to each second, dCO CO P and the flow rate of the mass of the sample.

Is given in the table 3 below, the results obtained.

Is clearly shown that for products with identical compositions (examples 1 and 9 and examples 3 and 12 respectively) the agents according to the invention have improved a OSC.