Title of Invention

"COMPOSITION BASED ON CERIUM OXIDE AND ON ZIRCONIUM OXIDE"

Abstract Composition based on cerium oxide and on zirconium oxide in a cerium/zirconium atomic ratio of at least 1:1, which has, after calcination for 6 hours at 900°C, a specific surface area of at least 35 m2/g and an oxygen storage capacity at 400°C of at least 1.5 ml O2/g.
Full Text COMPOSITION BASED ON CERIUM OXIDE AND ON ZIRCONIUM OXIDE
The present invention relates to a.
composition based on cerium oxide and on zirconium oxide with a high specific surface and with a high oxygen storage capacity, to its process of preparation and to its use in catalysis, in particular for automobile catalysis.
So-called multifunctional catalysts are currently used for the treatment of exhaust gases from internal combustion engines (automobile afterburning catalysis). The term "multifunctional catalyst" is understood to mean catalysts capable of carrying out not only oxidation, in particular of carbon monoxide and hydrocarbons present in exhaust gases, but also reduction, in particular of nitrogen oxides also present in these gases ("three-way" catalysts). Zirconium oxide and cerium oxide today appear as two constituents which are particularly important and advantageous for this type of catalyst.
To be effective, these catalysts must first of all exhibit a high specific surface, even at high temperature. In addition, it is known that cerium makes possible a buffering power with respect to variations in the oxygen content of the gas mixture to be treated and thus makes it possible to improve the performance of the catalyst with respect to the three main

pollutants, namely CO, HC and NOx. This buffering power is evaluated by the capacity to store oxygen in an oxidizing environment and to restore it in a reducing environment. However, this oxygen storage capacity decreases so much after exposure to high temperatures that the degree of conversion of the abovementioned pollutants may become insufficient.
For this reason, there exists a need for catalysts capable of being used at a high temperature and, in order to do so, exhibiting high specific surface stability combined, if possible, with stability of their oxygen storage capacity.
The present invention seeks to provide a catalyst composition which can meet this need.
The present invention therefore provides a composition based on cerium oxide and on zirconium oxide in a cerium/zirconium atomic ratio of at least 1:1 which has, after calcination for 6 hours at 900°C, a specific surface area of at least 35 m2/g and an oxygen storage capacity, measured at 400°C, of at least 1.5 ml O2/g.
The present invention also provides, as another embodiment, a composition based on cerium oxide, on zirconium oxide and on yttrium oxide in a cerium/zirconium atomic ratio of at least 1:1, which composition, after calcination for 6 hours at 900°C has a specific surface area of at least 35 m2/g and an oxygen storage capacity, measured at 400°C, of at least

1.5 ml 02/g.
The present invention additionally provides, as a third embodiment, a composition based on cerium oxide and on zirconium oxide in a cerium/zirconium atomic ratio of at least 1:1 and also on at least one oxide chosen from scandium oxide and rare-earth metal oxides other than cerium oxide, which composition, after calcination for 6 hours at 900°C, has a specific surface area of at least 35 m2/g.
In addition, the present invention provides a process for the preparation of the above compositions in which a mixture is prepared, in liquid medium, of a cerium compound, a zirconium compound and, if appropriate, an yttrium, scandium or rare-earth metal compound; the said mixture is heated; the precipitate obtained is recovered and this precipitate is calcined, wherein the said mixture is prepared by using a zirconium solution which is such that the amount of base necessary to reach the equivalent point during an acid/base titration of this solution confirms the condition that the molar ratio OH"/Zr Other characteristics, details and advantages of the invention will become still more fully apparent on reading the following description, as well as the various concrete but non-limiting examples intended to illustrate it.
In the continuation of the description, "specific surface area" is understood to mean the

B.E.T. specific surface determined by nitrogen adsorption in accordance with ASTM standard D 3663-78 laid down from the Brunauer-Emmett-Teller method described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)".
"Rare-earth metal" is understood to mean the elements from the group consisting of the elements of the Periodic Classification with an atomic number of between 57 and 71 inclusive, i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
The composition according to the invention can exist according to a number of embodiments but, in all cases, this composition is based at least on cerium oxide and on zirconium oxide in a cerium/zirconium atomic ratio of at least 1:1.
In the first embodiment described above, the composition can be composed essentially of cerium and of zirconium oxides. Compositions "composed essentially" of particular oxides typically do not contain any other metal oxide commonly used in catalysis. They can exhibit stability properties and in particular a catalytic activity in the absence of any other element of the oxide type commonly used in catalysis.
According to another embodiment of the invention, the composition additionally comprises yttrium oxide. It can be composed essentially, within the meaning of the term given above, of cerium oxide,

yttrium oxide and zirconium oxide.
According to a third embodiment, the
composition comprises at least one oxide chosen from scandium oxide and rare-earth metal oxides other than cerium oxide. It can, here again, be composed essentially, within the meaning of the term given above, of cerium oxide, of zirconium oxide and of the oxide or oxides of scandium or rare-earth metals other than cerium.
The rare-earth metal other than cerium is typically lanthanum, neodymium or praseodymium. Of course, the composition of the invention can comprise a number of rare-earth metal oxides or a combination of one or of a number of the rare-earth metal oxides with scandium oxide.
In the case of the third embodiment described above, the composition can additionally comprise yttrium oxide.
Typically, the compositions of the invention correspond to the formula CexZryMzO2 in which M represents at least one element chosen from yttrium, scandium and rare-earth metals other than cerium.
In the case where z=0, x can be from 0.5 to 0.95, more particularly from 0.5 to 0.9 and more particularly still from 0.6 to 0.8, these values being inclusive and x and y being linked by the relationship x+y=l.
In the case where z is not zero, z is

preferably at most 0.3 and is more preferably from 0.02 to 0.2. For these values of z, the x/y ratio is preferably from 1:1 to 19:1, more preferably from 1:1 to 9:1 and still more preferably from 1.5:1 to 4:1, the values other than 0 being inclusive and x, y and z being linked by the relationship x+y+z=l.
The compositions of the invention exhibit a specific surface area, after calcination for 6 hours at 900°C under air, of at least 35 m2/g. This surface area is preferably at least 40 m2/g and more preferably at least 45 m2/g-
The compositions of the invention typically also have specific surface areas which remain high even after calcination for 6 hours at 1000°C. Thus, the compositions of the invention typically have specific surface areas of at least 14 m2/g, preferably at least 20 mz/g and more preferably at least 30 m2/g after calcination for 6 hours at 1000°C. The presence of an element such as yttrium, a said rare-earth metal and scandium, as described above, makes it possible to obtain compositions exhibiting the highest specific surfaces.
Another characteristic of the compositions of the invention is their oxygen storage capacity. This capacity, measured at 400°C, is at least 1.5 ml of O2/g. It is preferably at least 1.8 ml of 02/g and more preferably at least 2 ml of O2/g. According to advantageous alternative forms of the invention, in

particular for compositions exhibiting an element such as yttrium, said rare-earth metals and scandium, this capacity can be at least 2.5 ml of O2/g, measured at 400°C. The capacities given above are capacities measured with respect to products which were aged beforehand for 6 hours at 900°C.
The compositions of the invention can advantageously exist in the form of a solid solution. The X-ray diffraction spectra of these compositions in fact reveal, within the latter, the existence of a single homogenous phase. For the compositions which are the richest in cerium, this phase corresponds to that of a crystalline eerie oxide CeO2, the unit cell parameters of which are more or less offset with respect to a pure eerie oxide, thus reflecting the incorporation of zirconium and, if appropriate, of the other element in the crystal lattice of the cerium oxide and thus the preparation of a true solid solution.
The process for the preparation of the compositions of the invention will now be described.
The first stage of the process according to the invention is preparing a mixture, in a liquid medium which is typically aqueous, of at least one cerium compound, at least one zirconium compound and, optionally, a yttrium, scandium or rare-earth metal compound other than cerium. This mixture is prepared by using a zirconium solution.

This zirconium solution can be obtained by acid attack on a zirconium compound. Typically, the zirconium compound is zirconium carbonate, hydroxide or oxide. The acid attack can be carried out with an inorganic acid, such as nitric acid, hydrochloric acid or sulphuric acid. Nitric acid is the preferred acid and the zirconium solution is preferably zirconyl nitrate obtained, for example, by the attack of nitric acid on a zirconium carbonate. The acid can also be an organic acid, such as acetic acid or citric acid.
According to the invention, this zirconium solution must have a molar ratio "OH/Zr The acid/base titration is carried out in a known way. In order for it to be carried out under optimum conditions, a zirconium solution having a concentration of approximately 3 x 10"2 mol per litre, expressed as elemental zirconium, can be titrated. A IN sodium hydroxide solution can be added thereto with stirring. Under these conditions, the equivalent point (change in the pH of the solution) is determined in a clear-cut way. This equivalent point is expressed by

the OH"/Zr molar ratio. It can Toe determined by known methods.
Mention may particularly be made, as cerium compounds, of cerium salts such as cerium(IV) salts, such as nitrates or eerie ammonium nitrates for example, which are particularly well suited in this instance. Ceric nitrate is particularly preferred. The cerium compound may be in the form of a solution. A solution of cerium(IV) salts can contain cerium in the cerous state but it is preferable for it to contain at least 85% of cerium(IV). An aqueous eerie nitrate solution can, for example, be obtained by reaction of nitric acid with a eerie oxide hydrate prepared conventionally by reaction of a solution of a cerous salt, for example cerous nitrate, and of an aqueous ammonia solution in the presence of hydrogen peroxide. Further, a eerie nitrate solution can be obtained by electrolytic oxidation of a cerous nitrate solution as described in FR-A-2,570,087.
It will be noted here that an aqueous solution of cerium(IV) salts to be mixed with the zirconium solution can exhibit a degree of initial free acidity, for example a normality from 0.1 to 4N. According to the present invention, it is just as possible to use an initial solution of cerium(IV) salts effectively exhibiting a degree of free acidity as mentioned above as a solution neutralized more or less exhaustively by addition of a base. Suitable bases for

neutralising the cerium salt solution include, for example, an aqueous ammonia solution or alternatively a solution of alkali metal (sodium, potassium and the like) hydroxides, but preferably an aqueous ammonia solution. It is possible, for a neutralised cerium salt solution, to define in practice a degree of neutralization (r) of the initial cerium solution by the following equation:
n3 -n2
r =
nl
in which nl represents the total number of moles of Ce(IV) present in the solution after neutralization; n2 represents the number of moles of OH* ions effectively necessary to neutralize the initial free acidity introduced by the aqueous cerium(IV) salt solution; and n3 represents the total number of moles of OH' ions introduced by the addition of the base. When a neutralised cerium salt solution is used, it is necessary that the amount of base added be less than the amount of base which would be necessary to obtain complete precipitation of the hydroxide species Ce(OH)4, that is, r must be less than 4. In practice, the limit can be set at degrees of neutralization which do not exceed r=l and preferably still do not exceed r=0.5.
The yttrium, scandium or rare-earth metal compounds are preferably compounds which are soluble in water.
Mention may be made, as scandium or rare-

earth metal compounds which can be used in the process of the invention, of, for example, the salts of inorganic or organic acids, for example of the sulphate, nitrate, chloride or acetate type. It will be noted that the nitrate is particularly well suited. These compounds can also be introduced in the form of sols. These sols can be obtained, for example, by neutralization by a base of a salt of these compounds.
The amounts of cerium, of zirconium and optionally of rare-earth metals, of yttrium and of scandium present in the mixture must correspond to the stoichioxnetric proportions required in order to obtain the final desired composition.
The initial mixture thus being obtained, it is then heated in accordance with the second stage of the process for the preparation of the compositions of the invention.
The temperature at which this heat treatment, also known as thermohydrolysis, is carried out can be between 80°C and the critical temperature of the reaction mixture, in particular between 80 and 350°C and preferably between 90 and 200°C.
This treatment can be carried out, according to the temperature conditions used, either at normal atmospheric pressure or under pressure, such as, for example, the saturated vapour pressure corresponding to the temperature of the heat treatment. When the treatment temperature is greater than the reflux

temperature of the reaction mixture (that is to say generally greater than 100°C), for example from 150 to 350°C, the operation can be carried out by introducing the aqueous mixture containing the abovementioned species into an enclosed space (closed reactor more commonly known as an autoclave)/ the necessary pressure then resulting only from the heating alone of the reaction mixture (autogenous pressure). Under the temperature conditions given above, and in aqueous medium, the pressure in the closed reactor can be, for example, from 1 bar (10s Pa) to 165 bar (165 x 105 Pa) , preferably from 5 bar (5 x 10s Pa) to 165 bar (165 x 10s Pa) . It is of course also possible to exert an external pressure which is then added to that resulting from the heating.
The heating can be carried out either under an air atmosphere or under an inert gas atmosphere, preferably nitrogen.
The duration of the treatment is not critical and can thus vary within wide limits, for example from 1 to 48 hours and preferably from 2 to 24 hours.
On conclusion of the heating stage, a solid precipitate is recovered which can be separated by any conventional solid/liquid separation technique, such as, for example, titration, settling, draining or centrifuging.
It may be advantageous, after the heating stage, to introduce a base, such as, for example, an

aqueous ammonia solution, into the precipitation mixture. This makes it possible to increase the recovery yields of the precipitated species.
It is also possible, in the same way, to add hydrogen peroxide after the heating stage.
The product as recovered can then be
subjected to washings with water and/or with aqueous ammonia, at a temperature between ambient temperature and the boiling temperature. In order to remove the residual water, the washed product can finally, optionally, be dried, for example in air, at a temperature which can vary from 80 to 300°C and preferably from 100 to 150°C. Drying can be continued until a constant weight is obtained.
It will be noted that it is of course possible, after recovery of the product and optional addition of the base or of hydrogen peroxide, to repeat a heating stage as described above one or a number of times, in an identical or nonidentical way, by then again placing the product in liquid medium, in particular in water, and by carrying out, for example, heat treatment cycles.
In a last stage of the process, the recovered precipitate, optionally after washing and/or drying, is calcined. According to a specific embodiment, it is possible, after the thermohydrolysis treatment and optionally after again placing the product in liquid medium and an additional treatment, directly to dry the

reaction mixture obtained by atomization.
The calcination is generally carried out at a temperature from 200 to 1200°C and preferably from 300 to 900°C. This calcination temperature must be sufficient to convert the precursors to oxides and it is also chosen as a function of the temperature of subsequent use of the catalytic composition, it being taken into account that the specific surface of the product becomes smaller as the calcination temperature employed becomes higher. The duration of the calcination can vary within wide limits, for example from 1 to 24 hours and preferably from 4 to 10 hours. The calcination is generally carried out under air but may be carried out, for example, under an inert gas.
The compositions of the invention as described above or as obtained in the processes mentioned above are provided in the form of powders but they can optionally be shaped in order to be provided in the form of granules, balls, cylinders or honeycombs of variable sizes. These compositions can be applied to any support commonly used in the field of catalysis, that is to say in particular thermally inert supports. This support can be chosen from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinels, zeolites, silicates, crystalline silicoaluminium phosphates or crystalline aluminium phosphates. The compositions can also be used in catalytic systems

compositions and with catalytic properties, on a substrate of the metal or ceramic monolith type, for example. The coating can itself also contain a support of the type of those mentioned above. This coating is obtained by mixing the composition with the support, so as to form a suspension which can subsequently be deposited on the substrate.
These catalytic systems and more particularly the compositions of the invention can have a great many applications. They are therefore particularly well suited to, and thus usable in, the catalysis of various reactions such as, for example, dehydration, hydrosulphurization, hydrodenitrification, desulphurization, hydrodesulphurization, dehydrohalogenation, reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, dismutation, oxychlorination, dehydrocyclization of hydrocarbons or other organic compounds, oxidation and/or reduction reactions, the Glaus reaction, treatment of exhaust gases from internal combustion engines, demetallation, methanation or the shift conversion.
In the case of these uses in catalysis, the compositions of the invention are employed in combination with precious metals. The nature of these metals and the techniques for the incorporation of the latter in these compositions are well known to the person skilled in the art. For example, the metals can

be platinum, rhodium, palladium or iridium and they can, in particular, be incorporated in the compositions by impregnation.
Among the uses mentioned, the treatment of exhaust gases from internal combustion engines (automobile afterburning catalysis) is a particularly advantageous application.
For this reason, the invention also relates to the use of a catalytic composition or of a catalytic system as described above in the manufacture of a catalyst for automobile afterburning.
Examples will now be given. The results with respect to the specific surfaces, the oxygen storage capacity and the calcination conditions (temperature and atmosphere) are given in the tables which follow the examples.
Description of the test to quantify oxygen storage
The buffering power of a composition with respect to oxygen is evaluated by its ability to store oxygen in an oxidizing environment and to restore it in a reducing environment. The test evaluates the capacity of the composition to successively oxidize pulses of carbon monoxide and to consume pulses of oxygen in order to reoxidize the composition. The method employed is known as alternating. References in the present specification to "oxygen capacity" are to oxygen capacity as determined by this method.

The carrier gas is pure helium at a flow rate of 10 1/h. Injections are made via a loop containing 16 ml of gas. The pulses of CO are produced by using a gas mixture containing 5% of CO diluted in helium, whereas the pulses of 02 are produced from a gas mixture containing 2.5% of 02 diluted in helium. The gases are analysed by chromatography using a thermalconductivity detector.
The amount of oxygen consumed makes it
possible to determine the oxygen storage capacity. The value characteristic of the oxygen storage power is expressed in ml of oxygen (under standard temperature and pressure conditions) per gram of product introduced and it is measured at 400°C. The measurements of oxygen storage power given in the table which follows are carried out with respect to products pretreated at 900°C under air for 6 hours in a muffle furnace.
EXAMPLE 1
This example illustrates the preparation of a mixed oxide of formula Ce0 62Zr0 3B02.
A eerie nitrate solution and a zirconyl nitrate solution are mixed in the stoichiometric proportions required to obtain the mixed oxide above. The zirconyl nitrate solution was obtained by attack on a carbonate using concentrated nitric acid. The solution corresponds, within the meaning defined above, to the condition that, as a molar ratio, OH"/Zr = 0.94.
The concentration of this mixture (expressed

as oxide of the various elements) is adjusted to 80 g/1. This mixture is then brought to 150°C for 4 hours.
An aqueous ammonia solution is then added to the reaction mixture so that the pH is greater than 8.5. The reaction mixture thus obtained is brought to boiling point for 2 hours. After separating by settling and then drawing off, the solid product is resuspended and the mixture thus obtained is treated for 1 hour at 100°C. The product is then filtered and then calcined at the temperature shown in the table of the results.
EXAMPLE 2
This example illustrates the preparation of a mixed oxide of formula Ze0 S5Zr0 31Nd0 M02.
A eerie nitrate solution, preneutralized by addition of NH4OH such that r = -0.22 (r being as defined above), a neodymium nitrate solution and a zirconyl nitrate solution, which corresponds, within the meaning defined above, to the condition that, as a molar ratio, OH"/Zr = 1.17, are mixed in the stoichiometric proportions required to obtain the mixed oxide above.
The procedure then followed is identical to that of Example 1 as far as the treatment stage for 1 hour at 100°C. The reaction mixture thus obtained is dried by atomization and then calcined at the temperature shown in the table of the results.

This example illustrates the preparation of a mixed oxide of formula Ce0 645Zr0 30Y0 05502.
The mixing of the solutions is the same as in Example 2, apart from the stoichiometric proportions, neodymium nitrate being replaced by yttrium nitrate.
The procedure then followed is identical to that of Example 2.
EXAMPLE 4
This example illustrates the preparation of a mixed oxide of formula Ce0 S5Zr0.31La0.04O2.
The mixing of the solutions and the procedure followed are the same as in Example 2, neodymium nitrate being replaced by lanthanum nitrate.
EXAMPLE 5
This example illustrates the preparation of a mixed oxide of formula Ce0 66Zr0 30Pr0 0402.
The mixing of the solutions and the procedure followed are the same as in Example 2, neodymium nitrate being replaced by praseodymium nitrate.
EXAMPLE 6
This example illustrates the preparation of a mixed oxide of formula Ce0.53Zr0 37La0 1002.
A eerie nitrate solution, a lanthanum nitrate solution and a zirconyl nitrate solution are mixed in the stoichiometric proportions required to obtain the mixed oxide above. The zirconyl nitrate solution corresponds, within the meaning defined above, to the condition that, as a molar ratio, OH"/Zr = 1.17.

The procedure then followed is identical to that of Example 1.
EXAMPLE 7
This example illustrates the preparation of a mixed oxide of formula Ce0 525Zr0-315Pr0 1602.
A eerie nitrate solution, preneutralized by addition of NH4OH such that r = -0.34, a praseodymium nitrate solution and a zirconyl nitrate solution, which corresponds, within the meaning defined above, to the condition that, as a molar ratio, OH~/Zr = 1.17, are mixed in the stoichiometric proportions required to obtain the mixed oxide above.
The procedure then followed is identical to that of Example 2.
EXAMPLE 8
This example illustrates the preparation of a mixed oxide of formula Ce0 535Zr0.373La0 047Nd0 04502.
The procedure then followed is identical to that of Example 1 but a zirconyl nitrate solution, which corresponds, within the meaning defined above, to the condition that, as a molar ratio, OH"/Zr = 1.17, is used.
COMPARATIVE EXAMPLE 9
This example illustrates the preparation according to the prior art of a mixed oxide of cerium, of zirconium and of yttrium of formula Ce0 65Zr0 30Y0 05O2.
A eerie nitrate solution and a zirconyl nitrate solution, which corresponds, within the meaning

defined above, to the condition that, as a molar ratio, OH~/Zr = 1.80, and an yttrium nitrate solution are mixed with stirring in the stoichiometric proportions required to obtain the mixed oxide above.
The mixture is then heat treated at 150°C for 4 hours. On conclusion of this treatment, an aqueous ammonia solution is introduced into the suspension obtained so as to bring the pH to 9.5, the whole mixture then being stirred for 30 minutes in order to homogenize.
A precipitate is then recovered by titration, is subsequently superficially dried and is then resuspended in water. This suspension is then heated at 100°C for 1 hour.
The product is again filtered, then dried in an oven at 120°C and finally calcined at 900°C for 6 hours.
COMPARATIVE EXAMPLE 10
This example illustrates the preparation according to the prior art, by precipitation, of a mixed oxide of cerium and of zirconium of formula
Ceo.7S5Zr0.23S°2'
A cerous nitrate solution and a zirconyl nitrate solution are mixed in the stoichiometric proportions required to obtain the mixed oxide above. The concentration as oxide of the elements is adjusted to 172 g/1.
This mixture thus obtained is added over

30 minutes to a solution containing aqueous ammonia, water and hydrogen peroxide. The product thus obtained is washed a number of times with dexnineralized water via a series of separations by settling and removals of the wash liquors. The product is subsequently filtered and then calcined at 900°C for 6 hours.
EXAMPLE 11
This example illustrates the synthesis of a mixed oxide of composition Ce0 657Zr0 306Pr0 03702 from a zirconyl nitrate solution, obtained by dissolution of a zirconyl carbonate in a nitric acid solution, which corresponds, within the meaning defined above, to the condition that, as a molar ratio, OK'/Zr = 0.86.
An aqueous solution containing cerium(IV) nitrate (non-preneutralized), praseodymium nitrate and zirconyl nitrate is prepared, in the stoichiometric proportions required to obtain the mixed oxide above, such that the total concentration as oxide of the mixture is 80 g/1.
The mixture is then heat treated at 150°C for 4 hours in an autoclave with constant stirring.
On conclusion of this treatment, aqueous ammonia is introduced into the suspension obtained so as to bring the pH to 9. The whole mixture is then maintained at 100°C for 2 hours.
The mother liquors are drawn off. The product is then resuspended and the pH of the suspension is readjusted to 9 by addition of the necessary amount of

aqueous ammonia. The mixture is kept stirring for 1 hour at 100°C. On conclusion of this washing operation, the product is again filtered, then dried overnight in an oven at 110°C and then calcined at the temperature shown in the table of the results.

(Table Remove)S.S.: Specific surface after calcination under air for 6 hours at the temperature shown ** OSC: Oxygen storage capacity


WE CLAIM;
1. Composition based on cerium oxide and on
zirconium oxide in a cerium/zirconium atomic ratio of
at least 1:1, which has, after calcination for 6 hours
at 900°C, a specific surface area of at least 35 m*/g
and an oxygen storage capacity at 400°C of at least
1.5 ml 02/g.
2. Composition according to claim 1, based
on yttrium oxide as well as on the cerium and zirconium
oxides.
3. Composition based on cerium oxide and on
zirconium oxide, in a cerium/zirconium atomic ratio of
at least 1:1, and on at least one oxide chosen from
scandium oxide and rare-earth metal oxides other than
cerium oxide, which composition has a specific surface
area, after calcination for 6 hours at 900°C, of at
least 35 m2/g-
4. Composition according to claim 3, which
has an oxygen storage capacity at 400°C of at least
1.5 ml of 02/g.
5. Composition according to claim 3 or 4,
wherein the rare-earth metal oxide is lanthanum,
neodymium or praseodymium oxide.
6. Composition according to any one of the
preceding claims, having a specific surface area, after
calcination for 6 hours at 900°C, of at least 40 m2/g-
7. Composition according to claim 6, having
a specific surface area, after calcination for 6 hours

at 900°C, of at least 45 mz/g.
8. Composition according to any one of the
preceding claims, having a specific surface area, after
calcination for 6 hours at 1000°C, of at least 14 m2/g.
9. Composition according to claim 8, having
a specific surface area, after calcination for 6 hours
at 1000°C, of at least 20 m2/g
10. Composition according to claim 9, having
a specific surface area, after calcination for 6 hours
at 1000°C, of at least 30 m2/g.
11. Composition according to any one of the
preceding claims, having an oxygen storage capacity at
400°C of at least 1.8 ml O2/g.
12. Composition according to claim 11,
having an oxygen storage capacity at 400°C of at least
2 ml 02/g.
13. Composition according to claim 12,
having an oxygen storage capacity at 400°C of at least
2.5 ml O2/g.
14. Composition according to any one of the
preceding claims having the formula CexZryMz02 wherein M
represents at least one element chosen from yttrium,
scandium and rare-earth metals other than cerium, z is
from 0 to 0.3, and wherein:

- when z = 0, x is from 0.5 to 0.95 and x+y=l;
and
- when z>0, the x:y ratio is from 1:1 to 19:1
and x+y+z=l.

15. Composition according to claim 14
wherein z is 0 and x is from 0.5 to 0.9.
16. Composition according to claim 15
wherein z is 0 and x is from 0.6 to 0.8.
17. Composition according to claim 14
wherein z is from 0.02 to 0.2.
18. Composition according to claim 14 or 17
wherein z is greater than 0 and the x:y ratio is from
1:1 to 9:1.
19. Composition according to claim 18
wherein the x:y ratio is from 1.5:1 to 4:1.
20. Composition according to any one of the
preceding claims in the form of a solid solution.
21. Process for the preparation of a
composition according to any one of the preceding
claims, which process comprises:
preparing, in a liquid medium, a mixture of a cerium compound, a zirconium compound and, optionally, a yttrium, scandium or rare-earth metal compound other than cerium by using a zirconium solution in which, as confirmed by acid/base titration, the molar ratio OH"/Zr s 1.65;
heating the mixture to obtain a precipitate;
recovering the precipitate; and
calcinating the recovered precipitate.
22. Process according to claim 21, wherein
the zirconium solution is a zirconyl nitrate solution
obtained by reaction of nitric acid with a zirconium

carbonate.
23. Process according to claim 21 or 22,
wherein the molar ratio "OH/Zr in the zirconium solution
s 1.5 as confirmed by acid/base titration.
24. Process according to claim 23 wherein
the molar ratio "OH/Zr in the zirconium solution as confirmed by acid/base titration.
25. Process according to any one of claims
21 to 24, wherein the cerium, scandium or rare-earth
metal compound is a cerium, scandium or rare-earth
metal salt.
26. Process according to claim 25 wherein
the cerium, scandium or rare-earth metal salt is a
nitrate.
27. A catalytic material comprising a
composition according to any one of claims 1 to 20 on a support of alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminium phosphate or crystalline aluminium phosphate type.
28. Catalytic system, comprising a coating
based on a composition according to any one of claims 1
to 20 provided on a substrate.
29. Use of a composition according to any
one of claims 1 to 20 or of a catalytic system
according to claim 28 in the treatment of exhaust gas
from an internal combustion engine.
30. Use of a composition according to any

one of claims 1 to 20, or of a catalytic system according to claim 27, in the manufacture of a catalyst for automobile afterburning.
31. Composition according to claim 1 substantially as described with
reference to any one of Examples 1 to 8 or 11.
32. Process according to claim 21 substantially as described with reference
to any one of Examples 1 to 8 or 11.



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1264-DEL-2005-Abstract-(28-11-2007).pdf

1264-del-2005-abstract.pdf

1264-DEL-2005-Claims-(28-11-2007).pdf

1264-del-2005-claims-02-03-2008.pdf

1264-del-2005-claims.pdf

1264-del-2005-correspondence-others-02-03-2008.pdf

1264-del-2005-correspondence-others.pdf

1264-DEL-2005-Description (Complete)-(28-11-2007).pdf

1264-del-2005-description (complete).pdf

1264-del-2005-form-1.pdf

1264-del-2005-form-18.pdf

1264-DEL-2005-Form-2-(17-05-2005).pdf

1264-del-2005-form-2.pdf

1264-del-2005-form-26.pdf

1264-DEL-2005-Form-3-(28-11-2007).pdf

1264-del-2005-form-3.pdf

1264-del-2005-form-5.pdf

1264-DEL-2005-GPA-(28-11-2007).pdf

1264-del-2005-gpa.pdf

1264-DEL-2005-Petition-137-(28-11-2007).pdf

1264-DEL-2005-Petition-138-(28-11-2007).pdf


Patent Number 235413
Indian Patent Application Number 1264/DEL/2005
PG Journal Number 31/2009
Publication Date 31-Jul-2009
Grant Date 01-Jul-2009
Date of Filing 17-May-2005
Name of Patentee RHONE-POULENC CHIMIE
Applicant Address 25 QUAI PAUL DOUMER, 92408 COURBEVOIE, CEDEX, FRANCE
Inventors:
# Inventor's Name Inventor's Address
1 MARYLINE AUBERT LA METAIRIE DE SAINT ELOI, 17540 ANGLIERS, FRANCE
2 THIERRY BIRCHEM 79, RUE PASCAL 75013 PARIS FRANCE
3 GILBERT BLANCHARD 5, ALLEE DES ACACIAS, 60330 LAGNY LE SEC. FRANCE.
PCT International Classification Number C04B 35/50
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 96 06051 1996-05-15 France