Title of Invention

"COMPOSITION BASED ON ZIRCONIUM OXIDE AND ON CERIUM OXIDE, PREPARATION PROCESS AND USE"

Abstract Composition based on zirconium oxide comprising cerium oxide, comprising, expressed in oxide from, at least 40% by weight of zirconium and at most 60% by weight of cerium, which has a specific surface of at least 30 m2/g after calcination for 6 hours at 900 degree centigrade, or which has a specific surface greater than 25 m2/g after calcination for 6 hours at 1000 degree centigrade and which is in the form of a pure solid solution of cerium oxide in zirconium oxide.
Full Text COMPOSITION BASED ON ZIRCONIUM OXIDE AND ON CERIUM OXIDE. PREPARATION PROCESS AND USE
The present invention relates to a composition based on zirconium oxide and on cerium oxide, to its process of preparation and to its use, in particular in catalysis.
So-called multifunctional catalysts are currently used in the treatment of exhaust gases from internal combustion engines (automobile afterburning catalysis). The term "multifunctional catalysts" 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 particularly important and advantageous constituents in this type of catalyst. To be effective, these catalysts must have a high specific surface, even at high temperature. Moreover, it is often advantageous to use these catalysts in the form of mixed oxides or of solid solutions.
There therefore exists a need for catalysts capable of being used at a high temperature and, for this, exhibiting high stability with respect to their specific surface.
The present invention provides a composition based on zirconium oxide comprising cerium oxide, which has a specific surface of at least 30 m2/g after calcination for 6 hours at 900°C and which is in the form of a pure solid solution of cerium oxide in zirconium oxide.
The present invention also provides, as another embodiment, a composition based on zirconium oxide comprising cerium oxide, which has a specific surface greater than 25 m2/g after calcination for 6 hours at 1000°C.
The present invention additionally provides, as a third embodiment, a composition based on zirconium oxide comprising cerium oxide and at least one doping element, which has a specific surface of at least 25 m2/g, more particularly of at least 3 0 m2/g, after calcination for 6 hours at 1000°C.
The present invention further provides a process for the preparation of the above compositions which comprises the following stages:
a mixture of a zirconium compound and a cerium(IV) compound in a liquid medium is prepared;
said mixture is heated at a temperature of greater than 100°C;
- the reaction mixture obtained on conclusion of the heating is brought to a basic pH;
the precipitate thus obtained is recovered; and
the said precipitate is calcined; the abovementioned doping element, if present, being added either to the starting mixture in liquid medium or to the reaction mixture obtained on conclusion of the heating.
The present invention also provides a second process for the preparation of the above compositions which comprises the following stages:
a mixture of a cerium compound and at least one zirconium oxychloride and, if appropriate, a compound of the
doping element in a liquid medium is prepared;
said mixture and a basic compound are brought together to form a precipitate;
said precipitate is recovered; and said precipitate is calcined. The single figure of the drawing is an X-ray-diffraction spectrum of a composition of the invention. The compositions of the invention are based on zirconium oxide. They additionally comprise cerium oxide. As indicated above, the composition of the first embodiment of the invention has a specific surface of at least 30 m2/g after calcination for 6 hours at 900°C and is in the form of a pure solid solution of cerium oxide in zirconium oxide.
Specific surface is understood to mean, here and in the remainder of the description, the B.E.T. specific surface determined by nitrogen adsorption in accordance with the 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)".
For this embodiment, the specific surface of the composition can be at least 40 m2/g after calcination for 6 hours at 900°C. Specific surfaces greater than 45 m2/g after calcination for 6 hours at 900°C can even be obtained. The other characteristic of the compositions according to this first embodiment is the fact that they are provided in the form of a pure solid solution of cerium oxide in zirconium oxide.
This is understood to mean that the cerium is
present entirely in solid solution in the zirconium. The X-ray diffraction spectra of these compositions reveal in particular the existence of a clearly identifiable single phase corresponding to that of a zirconium oxide crystallized in the cubic or quadratic system, thus reflecting the incorporation of the cerium within the crystal lattice of the zirconium oxide and thus the production of a true solid solution.
The compositions of the second embodiment have, after calcination for 6 hours at 1000°C, a specific surface greater than 25 m2/g. They can also, according to a specific alternative form, be provided in the form of a pure solid solution of cerium oxide in zirconium oxide.
According to a third embodiment of the invention, the composition additionally contains a doping element. Examples of the doping element are a rare-earth metal, alkaline-earth metal, aluminium, thorium, scandium, gallium, titanium, niobium, tantalum or a mixture thereof.
A rare-earth metal is understood to mean the elements from the group composed of yttrium and the elements of the periodic classification with an atomic number of from 57 to 71 inclusive. Mention may more particularly be made of yttrium, lanthanum, neodymium, praseodymium, europium and samarium.
Mention may more particularly be made, for the alkaline-earth metals, of magnesium, calcium and barium.
The compositions of this embodiment have a specific surface of at least 25 m2/g after calcination for 6 hours at 1000°C. This specific surface can more particularly be least
30 m2/g. In certain cases, this specific surface can reach at least 40 m2/g and exceed 45 m2/g.
These same compositions can, moreover, have a specific surface of at least 50 m2/g, more particularly of at least 60 m2/g, after calcination for 6 hours at 900°C.
The compositions comprising a doping agent can also be provided in the form of a solid solution of cerium oxide and of the doping agent in zirconium oxide. The X-ray diffraction spectra of these compositions are of the same type as those described above.
Compositions comprising at least lanthanum as a doping agent can have a specific surface, after calcination for 6 hours at 1100°C, of at least 5 m2/g, more particularly of at least 10 m2/g.
Expressed in the form of oxides, here and throughout the description, except when otherwise indicated, the compositions according to the invention generally contain at least 40% by weight of zirconium and at most 60% by weight of cerium. More particularly, they may, for example, have a Zr:Ce atomic ratio of equal to or greater than 1:1, that is to say contents equal to or greater than 42% by weight of zirconium and equal to or less than 58% by weight of cerium. According to another embodiment, the compositions according to the invention contain at least 51% by weight of zirconium and at most 49% by weight of cerium. These proportions, according to still more specific embodiments of the invention, can be more precisely at least 55% by weight of zirconium and at most 45% by weight of cerium and, more particularly still, at least 65% by weight of zirconium and
at most 35% by weight of cerium.
According to other embodiments of the invention, the cerium proportion can be at most 3 0% and more particularly at most 2 0%.
The minimum cerium content is preferably at least 1%, more particularly greater than 10% and more particularly still at least 15%.
When the compositions of the invention additionally contain a doping element, the content of this element, still expressed in oxide form, may, for example, be from 0.1 to 50% by weight, in particular from 0.1 to 45% by weight, more particularly from 0.1 to 20% by weight and preferably from 1 to 10% by weight, with respect to the whole of the composition.
Finally, it should be noted that the compositions of the invention can additionally comprise hafnium. Hafnium is an element present with zirconium in currently avaiTablte-zirconium sources. Depending on the nature of this source in particular, the hafnium content, expressed as oxide, may, for example, be from 0.01 to 25% with respect to the whole of the composition.
The processes for the preparation of the compositions of the invention will now be described.
Two alternative forms of the process exist. The first form is athermohydrolysis process and the second form is a coprecipitation process.
According to the first form, the first stage of the process consists in preparing a mixture, in liquid medium, of a zirconium compound and of a cerium(IV) compound and, if
appropriate, of the doping element. The various compounds of the mixture are present in the stoichiometric proportions necessary for obtaining the desired final composition.
The liquid medium is generally water.
The compounds are preferably soluble compounds. This
can be in particular zirconium and cerium salts.
The mixture can, without distinction, be obtained
either from compounds initially in the solid state which will subsequently be introduced into a water vessel heel, for example, or alternatively directly from solutions of these
compounds, followed by mixing the said solutions in any order.
The zirconium compounds may be, for example, zirconium sulphate, zirconyl nitrate or zirconyl chloride. The most widely used is zirconyl nitrate. Zirconyl chloride is particularly well suited for obtaining products with the highest specific surfaces.
The doping element, if required, is commonly introduced in the form of a salt, for example in nitrate form. Introduction in the form of a sol is not excluded, when such a type of sol exists.
Mention may particularly be made, as water-soluble cerium compounds, of cerium(IV) salts, such as nitrates or eerie ammonium nitrates, which are particularly well suited in this instance. Ceric nitrate is preferably used. It is advantageous to use salts with a purity of at least 99.5% and more particularly of at least 99.9%. The solution of cerium(IV) salts can, without disadvantage, contain cerium in the cerous state but it is desirable for it to contain at
least 85% of cerium(IV). An aqueous cerie 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. Use can also preferably be made of a eerie nitrate solution obtained according to the process of electrolytic oxidation of a cerous nitrate solution, as described in FR-A-2,570,087, which constitutes in this instance an advantageous starting material.
It should be noted here that the aqueous solutions of cerium(IV) salts and of zirconyl salts can exhibit a degree of initial free acidity. According to the present invention, it is just as possible to use an initial solution of cerium(IV) and zirconium salts effectively exhibiting a degree of free acidity as mentioned above as solutions which would have been neutralized beforehand more or less exhaustively. This neutralization can be carried out by addition of a basic compound to the abovementioned mixture, so as to limit this acidity. This basic compound can be, for example, an aqueous ammonia solution or alternatively a solution of alkali metal (e.g. sodium or potassium) hydroxides but is preferably an aqueous ammonia solution. It is then possible to define in practice a degree of neutralization (r) of the initial cerium and zirconium solution by the following equation:
(Equation Removed)
in which nl represents the total number of moles of Ce(IV) and of zirconium 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) and zirconium salt solutions; and n3 represents the total number of moles of 0H~ ions introduced by the addition of the base. When the "neutralization" alternative form is implemented, use is made in all cases of an amount of base which absolutely must be less than the amount of base which would be necessary to obtain complete precipitation of the cerium zirconium hydroxide species, this amount depending on the composition synthesized. In practice, the limit is therefore set at a degree of neutralization which does not exceed 2.
The initial mixture thus obtained is then heated in accordance with the second stage of the process according to the invention.
The temperature at which this heat treatment, also known as thermohydrolysis, is carried out is greater than 100°C. It can thus be from 100°C to the critical temperature of the reaction mixture, in particular from 100 to 350°C and preferably from 100 to 200°C.
The heating operation can be carried out by introducing the liquid mixture containing the abovementioned species into an enclosed space (closed reactor of the autoclave type), 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 media, it is thus possible to specify, by way of
illustration, that the pressure in the closed reactor is greater than 1 bar (105 Pa) to 165 bar (1.65 x 107 Pa), preferably from 5 bar (5 x 105 Pa) to 165 bar (1.65 x 107 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 also be carried out in an open reactor for temperatures in the region of 100°C.
The heating can be carried out either under air 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. Likewise, the temperature rise takes place at a rate which is not critical and it is thus possible to reach the set reaction temperature by heating the mixture, for example, for from 3 0 minutes to 4 hours, these values being given entirely by way of indication.
On conclusion of this second stage, the reaction mixture obtained is brought to a basic pH. This operation is carried out by adding a base, such as for example an aqueous ammonia solution, to the mixture.
A basic pH is understood to mean a pH of greater than 7 and preferably greater than 8.
Although this alternative form is not preferred, it is possible to introduce the doping element or elements, in particular in the form which has been described above, into the reaction mixture obtained on conclusion of the heating, in particular at the time of the addition of the base.
On conclusion of the heating stage, a solid
precipitate is recovered which can be separated from its mixture by any conventional solid/liquid separation technique, such as, for example, filtration, settling, draining or centrifuging.
The product as recovered can then be subjected to washings, which are then carried out with water or optionally with a basic solution, for example an aqueous ammonia solution. Washing can be carried out by resuspending the precipitate in water and keeping the suspension thus obtained at a temperature which can range up to 100°C. In order to remove the residual water, the washed product can optionally be dried, for example in an oven or by spraying, at a temperature of, for example, from 80 to 300°C and preferably from 100 to 200°C.
According to a specific alternative form of the invention, the process comprises a maturing.
This maturing can be carried out directly on the reaction mixture obtained after addition of a base in order to result in a basic pH. As the addition of a base has the effect of cooling the reaction mixture, the maturing is carried out by reheating the mixture. The temperature to which the mixture is heated is at least 40°C, more particularly at least 60°C and more particularly still at least 100°C. The mixture is thus kept at a constant temperature for a period of time which is commonly at least 30 minutes and more particularly at least 1 hour. The maturing can be carried out at atmospheric pressure or optionally at a higher pressure.
The maturing can also be carried out on a suspension
obtained after returning the precipitate to water. The pH of this suspension can be adjusted to a value greater than 7 and preferably greater than 8.
It is possible to carry out a number of maturings. Thus, the precipitate obtained after the maturing stage and optionally a washing can be resuspended in water and then another maturing of the mixture thus obtained can be carried out. This other maturing is carried out under the same conditions as those which have been described for the first. Of course, this operation can be repeated a number of times.
In a final stage of the process according to the invention, the precipitate recovered, optionally after washing and/or drying, is calcined. This calcination makes it possible to develop the crystallinity of the solid solution formed and it can also be adjusted and/or chosen according to the subsequent temperature of use intended for the composition according to the invention, while taking into account the fact that the specific surface of the product becomes smaller as the calcination temperature used becomes higher. Such a calcination is generally carried out under air but a calcination carried out, for example, under an inert gas or under a controlled atmosphere (oxidizing or reducing) is very clearly not excluded.
In practice, the calcination temperature is generally from 300 to 1000°C.
Even after calcinations at high temperatures, that is to say in particular temperatures greater than those which are strictly necessary to clearly demonstrate, by X-rays, the formation of the desired solid solution, the compositions
according to the invention retain entirely acceptable specific surfaces.
A calcination can be carried out in two steps. A first calcination can be carried out at a relatively low temperature, for example at 300-400°C, and a second at a higher temperature, for example at 500-800°C. This two-step calcination can be carried out in the same furnace comprising differentiated heating regions.
The second form of the process will now be described.
The first stage of the second form consists in preparing a mixture comprising a cerium compound, zirconium oxychloride (ZrOCl2) and a compound of the doping element.
The cerium compound can be a cerium(III) or cerium(IV) compound. The compounds are preferably soluble compounds. That which has been said above with respect to cerium compounds, and in particular cerium(IV) compounds, and compounds of the doping element also applies here. A cerium(IV) compound is preferably used, such a compound resulting in the products with the highest specific surfaces. The various compounds of the mixture are present in the stoichiometric proportions necessary for obtaining the desired final composition.
In a second stage, said mixture and a basic compound are brought together. Products of the hydroxide or carbonate type can be used as the base or basic compound. Mention may be made of alkali metal or alkaline-earth metal hydroxides. Secondary, tertiary or quaternary amines can also be used. However, amines and aqueous ammonia may be preferred, insofar
as they decrease the risks of pollution by alkali metal or alkaline-earth metal cations. Mention may also be made of urea. The reactants can be introduced in any order, it being possible for the basic compound to be introduced into the mixture or vice versa. It is also possible for the reactants to be introduced simultaneously into the reactor.
Addition can be carried out in a single step, gradually or continuously and it is preferably carried out with stirring. This operation can be carried out at a temperature of from room temperature (18-25°C) to the reflux temperature of the reaction mixture, it being possible for the latter to reach 120°C, for example. It is preferably carried out at room temperature.
It may be noted that it is possible, in particular in the case of a process using a cerium(III) compound, to add an oxidizing agent, such as hydrogen peroxide, either to the starting mixture or during introduction of the basic compound.
At the end of the addition of the basic solution, the reaction mixture can further optionally be kept stirring for a while, in order to bring precipitation to completion.
It is also possible, at this stage of the process, to carry out a maturing. This can be carried out directly on the reaction mixture obtained after addition of the basic compound or on a suspension obtained after returning the precipitate to water. The maturing is carried out by heating the mixture. The temperature to which the mixture is heated is at least 40°C, more particularly at least 60°C and more particularly still at least 100°C. The mixture is thus
maintained at a constant temperature for a period of time which is commonly at least 3 0 minutes and more particularly at least 1 hour. The maturing can be carried out at atmospheric pressure or optionally at a higher pressure.
On conclusion of the precipitation stage, a large amount of a solid precipitate is recovered which can be separated from its mixture by any conventional technique.
The washing and calcination stages are then carried out in the same way as that described for the first embodiment.
The compositions of the invention as described above or as obtained in the processes mentioned above are generally 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, for example, 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 comprising a coating (wash coat), which possesses catalytic properties and which is based on these compositions, 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 then 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 can be used 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 Claus 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.
Finally, the compositions of the invention can be used in the preparation of ceramics.
The present invention will now be further described in the following Examples. EXAMPLE 1
A zirconyl nitrate (crystalline zirconyl nitrate, Prolabo) solution is added to a cerium(IV) nitrate solution in a proportion, by weight of oxide, of 80/20. Aqueous ammonia is added to the mixture of the two solutions, so as to obtain a ratio r, as defined above, of 0.7. The concentration is adjusted to 80 g/1 and the solution is then brought to 150°C for 6 h. After cooling, the pH of the reaction mixture is brought to 8.5 using an ammonia solution. The temperature is then brought to 100°C. The mother liquors are then removed by settling and the equivalent amount of water is added. The reaction mixture is again heated for 1 hour at 100°C. The reaction mixture is filtered under pressure. The cake obtained is calcined for 6 h at 900°C and for 6 h at 1000°C. The specific surfaces are respectively 36 and 21 m2/g.
X-ray diffraction analysis (Figure 1) shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 2
A solution of zirconyl nitrate (obtained by attack of nitric acid on a Zr carbonate) is added to a cerium(IV) nitrate solution in a proportion, by weight of oxide, of 80/2 0, such that the ratio r is 0.5. The concentration is adjusted to 80 g/1 and the solution is then brought to 150°C
for 6 hours. After cooling, the pH of the reaction mixture is brought to 8.5 using an ammonium solution. The temperature is then brought to 100°C. After cooling, the mother liquors are removed by settling and an equivalent amount of water is added. The reaction mixture is again brought to 100°C. After settling, the supernatant is removed and the product is dried by spraying. The powder obtained is calcined for 2 hours at 650°C.
The specific surfaces of the oxide thus obtained are respectively 45 and 25 m2/g for 6 hours at 900°C and 1000°C.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 3
A zirconyl nitrate solution is added to a Ce(IV) nitrate solution in a proportion, by weight of oxide, of 63/37 such that the ratio r is 0.35. The concentration is adjusted to 80 g/1 and the solution is then brought to 150°C for 6 hours. After cooling, the pH of the mixture is brought to 8.5 using an ammonia solution. The mixture thus obtained is filtered and then calcined for 2 hours at 400°C.
The specific surfaces of the oxide thus obtained are respectively 43 and 20 m2/g for 6 hours at 900°C and 1000°C.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 4
A solution of zirconyl chloride (obtained by dissolving the crystalline salt) is added to a Ce(IV) nitrate solution in a proportion, by weight of oxide, of 80/20 such that the ratio r is 0.07. The concentration is adjusted to 80
g/1 and the solution is then brought to 150°C for 6 hours. After cooling, the pH of the reaction mixture is brought to 8.5 using an ammonia solution. The temperature is then brought to 100°C. After cooling, the mother liquors are removed by settling and an equivalent amount of water is added. The reaction mixture is again brought to 100°C. After cooling, the product is filtered off.
After calcination for 6 hours at 900°C and 1000°C, the specific surfaces of the oxides are 40 and 29 m2/g respectively.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 5
The starting solution is composed of a mixture of cerium(IV) nitrate, of zirconyl nitrate and of lanthanum nitrate in proportions, by weight of oxide, of 19/76/5 (ratio r = 0.5). The preparation is carried out as in Example 2. Calcination of the product is carried out for 2 hours at 600°C.
After calcination for 6 hours at 900°C, 1000°C and 1100°C, the specific surfaces are 60, 41 and 11 m2/g respectively.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 6
The starting solution is composed of a mixture of cerium(IV) nitrate, of zirconyl nitrate and of praseodymium nitrate in proportions, by weight of oxide, of 19/76/5 (ratio r = 0.5). The preparation is carried out as in Example 2.
Calcination of the product is carried out for 2 hours at 600°C.
After calcination for 6 hours at 900°C and 1000°C, the specific surfaces are 58 and 33 m2/g respectively.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 7
A zirconyl nitrate and neodymium nitrate solution is added to a Ce(IV) nitrate solution in the proportions, by weight of oxide, of 76/5/19 (ratio r = 0.5). The concentration is adjusted to 80 g/1 and the solution is then brought to 150°C for 6 hours. After cooling, the pH of the mixture is brought to 8.5 using an ammonia solution. The mixture thus obtained is filtered and then calcined for 2 hours at 400°C.
The specific surfaces of the oxide thus obtained are respectively 55 and 33 m2/g for 6 hours at 900°C and 1000°C.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 8
The starting solution is composed of a mixture of cerium(IV) nitrate, of zirconyl nitrate, of lanthanum nitrate and of praseodymium nitrate in proportions, by weight of oxide, of 18/72/5/5 (ratio r = 0.5). The preparation is carried out as in Example 2. Calcination of the product is carried out for 2 hours at 800°C.
After calcination for 6 hours at 900°C, 1000°C and 1100°C, the specific surfaces are 64, 49 and 13 m2/g respectively.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 9
A solution of a mixture of Ce(IV) nitrate, of La nitrate and of Zr oxychloride, in proportions, by weight of oxide, of 17/5/78, at a concentration of 172 g of oxide/1, is precipitated by addition of this solution to an ammonia solution. After settling the pulp obtained, the mother liquors are removed and an equivalent amount of water is added. The reaction mixture is heated for 1 hour at 100°C. After settling and removing the mother liquors, an equivalent volume of water is again added and the suspension is then filtered. The cake is then calcined for 2 hours at 400°C and then for 1 hour at 750°C. After calcination for 6 hours at 900°C and for 6 hours at 1000°C, the specific surfaces are 63 and 51 m2/g respectively.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase. EXAMPLE 10
A zirconyl nitrate (crystalline zirconyl nitrate, Prolabo) solution is added to a cerium(IV) nitrate solution in a proportion, by weight of oxide, of 80/20. The concentration is adjusted to 80 g/1 and the solution is then brought to 150°C for 6 h. After cooling, the pH of the reaction mixture is brought to 8.5 using an ammonia solution. The temperature is then brought to 100°C. The mother liquors are then removed by settling and the equivalent amount of water is added. The reaction mixture is again heated for 1 hour at 100°C. The reaction mixture is filtered under
pressure. The cake obtained is resuspended in order to be dried by spraying. The product obtained is calcined for 6 h at 900°C and for 6 h at 1000°C. The specific surfaces are 32 and 15 m2/g respectively. EXAMPLE 11
A solution of a mixture of Ce(III) nitrate and of Zr oxychloride, in a proportion, by weight of oxide, of 20/80, at a concentration of 172 g of oxide/1, is precipitated by addition of this solution to an ammonia solution containing hydrogen peroxide. After settling the pulp obtained, the mother liquors are removed and an equivalent amount of water is added. The reaction mixture is heated for 1 hour at 100°C. After settling and removing the mother liquors, an equivalent volume of water is again added and the suspension is then filtered. The cake is then calcined for 2 hours at 400°C. After calcination for 6 hours at 900°C and for 6 hours at 1000°C, the specific surfaces are 35 and 25 m2/g respectively.
X-ray diffraction analysis shows that the oxide obtained is in the form of a pure solid solution phase.










WE CLAIM
1. Composition based on zirconium oxide comprising cerium oxide, comprising, expressed in oxide form, from 40 to 99% by weight of zirconium and 5 from 1 to 60% by weight of cerium, which has a specific surface of at least 30 m2fg after calcintion for 6 hours at 900°C, and which has a specific surface greater than 25 m2/g after calcination lot 6 hours at 1000°C and which is in the roan of a pure solid solution of cerium oxide in zirconium oxide.
2. Composition as claimed in claim 1 which also comprises at least one doping element in an amount of from 0.1 to 50% by weight, expressed in oxide form with respect to the whole of the composition.
3. Composition as claimed in claim 2, which has a specific surface or at least 30 m2/g after calcination for 6 hours at 1000°C.
4. Composition as claimed in claim 3, which has a specific surface of at least 40 m2/g after calcination for 6 hours at 1000°C.
5. Composition as claimed in any one of claims 2 to 4 which is in the form of a pure solution of cerium oxide and of the doping element in zirconium oxide.
6. Composition as claimed in any one of claims 2 to 5, wherein the doping element is a rare-earth metal, alkaline-earth metal, aluminium, thorium, scandium, gallium, titanium, niobium, tantalum or a mixture thereof.
7. Composition as claimed in claim 6, wherein the doping element is lanthanum and which composition has a specific surface of at least 5 m /g after calcination for 6 hours at 1100°C.
8. Composition as claimed in any one of claims 2 to 7, which comprises from 0.1 to 45% by weight of the doping element.
9. Composition as claimed in claim 8, which comprises from 0.1 to 20% by weight of the doping element.
10. Composition as claimed in any one of claims 1 to 8, which has a Zr:Ce atomic ratio of equal, to or greater than 1:1.
11. Composition as claimed in any one claims 1 to 10 which comprises at least 51% by weight of zirconium and at most 49% by weight of cerium.
12. Composition as claimed in claim 11, which comprises at least 55% by weight of zirconium and at most 45% by weight of cerium.
13. Composition as claimed in claim 12 which comprises at least 55% by weight of zirconium and at most 35% by weight of cerium.
14. Composition as claimed in any one of claims 1 to 13 which additionally comprises hafnium in an amount, expressed in oxide form, of from 0.01 to 25% by weight.
15. Process for the preparation of a composition based on zirconium oxide comprising cerium oxide comprising, expressed in oxide form, at least 40% by weight of zirconium and at most 60% by weight of cerium which has a specific surface of at least 30 m2/g after calcination for 6 hours at 900°C or which has a specific surface greater than 25 m2/g after calcination for 6 hours at 1000°C and which is in the form, of a pure solid solution of cerium oxide in zirconium oxide, which process comprises the following stages:
- a mixture of a cerium compound and at least one zirconium oxychloride and, if appropriate, a compound of the doping element, as described, above, in a liquid medium is prepared;
- said mixture and a basic compound are brought together to form a precipitate;
- maturing, at a temperature of at least 100°C, either the reaction medium obtained in the preceding step, or a suspension obtained after taking up precipitate from said reaction medium in water:
then
the precipitate thus obtained is recovered; and
said precipitate is calcined to obtain the composition.
16. Process as claimed in Claim 15, wherein the doping element is lanthanum and in which the composition produced has a specific surface of least 5 m /g after calcination for 6 hours at 1100°C.
17. Process as claimed in claim 15 or claim 16, wherein the doping element is present in an amount of from 0.1 to 45% by weight.
18. Process as claimed in claim 17 wherein the doping element is present an amount of from 0.1 to 20% by weight.
19. Process as claimed in any one of claims 15 to 18, wherein the composition has a Zr:Ce atomic ratio of equal to or greater than 1:1.
20. Process as claimed in any one of claims 15 to 19, wherein the composition comprises at least 51% by weight of zirconium and at most 49% by weight of cerium.
21. Process as claimed in claims. 20, wherein the composition comprises at least 55% by weight of zirconium and at most 45% by weight of cerium.
22. Process as claimed in claim 21 wherein the composition comprises at least 65% by weight of zirconium and at most 35% by weight of cerium.
23. Process as claimed in any one of claims 13 to 20, wherein the composition additionally comprises, expressed in oxide form, 0.01 to 25% by weight of hafnium.
24. Process as claimed in any one of claims 15 to 23 wherein the zirconium compound is zirconyl nitrate or zirconyl chloride and the cerium compound is cerium nitrate or cerium ammonium nitrate.
25. Process as claimed in any one of claims 15 to 24, wherein a basic compound is added to the mixture in a liquid medium in order to limit the free acidity of said mixture.
26. Coating which possesses catalytic properties, which comprises a composition produced by a process as claimed in any one of claims 1 to 14, on a support of alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminium phosphate or crystalline aluminium phosphate type.
27. Catalytic system which comprises a coating based or a composition produced by a process as claimed in any one of claims 15 to 26, on a substrate.
28. Process as claimed in anyone of claims 13 to 25, substantially as described in any one of Examples 20 to 38.
29. Composition substantially as described in any one of the examples.

Documents:

1476-del-2005-abstract.pdf

1476-del-2005-Assignment-(27-08-2014).pdf

1476-DEL-2005-Claims-(28-04-2010).pdf

1476-del-2005-claims.pdf

1476-DEL-2005-Correspondence Others-(03-11-2011).pdf

1476-del-2005-Correspondence Others-(09-01-2014).pdf

1476-del-2005-Correspondence Others-(27-08-2014).pdf

1476-DEL-2005-Correspondence-Others-(28-04-2010).pdf

1476-del-2005-correspondence-others.pdf

1476-del-2005-description (complete).pdf

1476-del-2005-drawings.pdf

1476-del-2005-form-1.pdf

1476-del-2005-form-13.pdf

1476-del-2005-form-18.pdf

1476-del-2005-form-2.pdf

1476-DEL-2005-Form-3-(28-04-2010).pdf

1476-del-2005-form-3.pdf

1476-del-2005-form-5.pdf

1476-DEL-2005-GPA-(28-04-2010).pdf

1476-del-2005-gpa.pdf

Petition.pdf


Patent Number 265593
Indian Patent Application Number 1476/DEL/2005
PG Journal Number 10/2015
Publication Date 06-Mar-2015
Grant Date 27-Feb-2015
Date of Filing 08-Jun-2005
Name of Patentee RHONE-POULENC CHIMIE
Applicant Address 25 QUAI PAUL DOUMER, 92408 COURBEVOIE CEBEX, FRANCE.
Inventors:
# Inventor's Name Inventor's Address
1 GILBERT BLANCHARD 5, ALLEE DES ACACIAS, LAGNY-LE-SEC, 60330 LE PLESSIS BELLEVILLE, FRANCE.
2 MARYLINE AUBERT LA METAIRIE DE SANIT ELOI, 17540 -ANGLIERS, FRANCE.
3 THIERRY BIRCHEM 79, RUE PASCAL, 75013 PARIS, FRANCE.
4 OLIVIER TOURET 20, RUE GENERAL GUILLAUMAT, 17000-LA ROCHELLE, FRANCE.
PCT International Classification Number B01J8/02
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 9507979 1995-07-03 France