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  Composition based on oxides of zirconium, praseodymium, lanthanum or neodymium, method for the preparation and use thereof in a catalytic systemUSPTO Application #: 20080020925Title: Composition based on oxides of zirconium, praseodymium, lanthanum or neodymium, method for the preparation and use thereof in a catalytic system Abstract: The composition is based on zirconium oxide and at least one additive selected from zirconium oxide and at least one additive chosen from praseodymium, lanthanum or neodymium oxides, has a specific surface of at least 29 m 2/g after calcination at 1000° C. during a period of 10 hoursand is is obtained by a method wherein a mixture of zirconium compounds and additive is precipitated with a base; the medium thus obtained, containing a precipitate, is heated and a compound chosen from anionic surfactants, non-ionic surfactants, polyethylene glycols, carboxylic acids and the salts thereof and surfactants such as the ethoxylates of caroboxymethyl fatty alcohols is added to the compound and the precipitate is calcinated; the composition can be used as a catalyst. (end of abstract) Agent: Jean-louis Seugnet Rhodia - Cn 7500, Cranbury, NJ, US Inventors: Olivier Larcher, Philippe Moissonnier, Emmanuel Rohart USPTO Applicaton #: 20080020925 - Class: 502303 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080020925. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001]The present invention relates to a composition based on zirconium oxide, on an additive selected from the oxides of praseodymium, lanthanum and neodymium, its method of preparation and its use in a catalytic system. [0002]Catalysts called multifunctional catalysts are used at the present time for treating exhaust gases of internal combustion engines (automobile postcombustion catalysis). Multifunctional catalysts are catalysts capable not only of obtaining the oxidation of the carbon monoxide and hydrocarbons present in the exhaust gases, but also of reducing the nitrogen oxides also present in these gases ("three-way" catalysts). Catalysts based on zirconium oxide or cerium oxide are known today as particularly advantageous for this type of reaction. [0003]To be effective, these catalysts must have a high specific surface area, and there is a continuing search for catalysts which can be used at increasingly high temperatures, and, for this purpose, have a more stable specific surface area. [0004]Thus it is the object of the invention to develop a catalytic composition to meet this requirement. [0005]For this purpose, the composition of the invention is based on zirconium oxide and is characterized in that it further comprises at least one additive selected from the oxides of praseodymium, lanthanum and neodymium, and in that it has a specific surface area of at least 29 m.sup.2/g after calcination for 10 hours at 1000.degree. C. [0006]The composition of the invention thereby has the advantage of preserving a high specific surface area at a temperature of 1000.degree. C. or even more. Furthermore, the catalysts based on this composition may also have high efficiency at low temperature even with a low precious metal content. [0007]Other features, details and advantages of the invention will appear even more clearly from a reading of the description that follows, and from the various concrete but nonlimiting examples provided to illustrate it. [0008]In the rest of the description, specific surface area means the BET specific surface area determined by nitrogen adsorption according to standard ASTM D 3663-78 established using the Brunauer-Emmett-Teller method described in the periodical The Journal of the American Chemical Society, 60, 309 (1938). [0009]The periodic table of elements referred to in the present description is the one published in the Supplement au Bulletin de la Societe Chimique de France No. 1 (January 1966). Rare earth means elements of the group consisting of yttrium and the elements of the periodic table with atomic numbers of 57 to 71 inclusive. [0010]Furthermore, the calcinations after which the surface area values are given are calcinations in air unless otherwise indicated. [0011]The contents are given as oxides unless otherwise indicated. [0012]The main features of the compositions of the invention are the nature of their components and their specific surface area. [0013]The compositions of the invention are based on zirconium oxide ZrO.sub.2, this oxide being the essential or majority component. The compositions further comprise at least one additive, which constitutes the remainder of the composition and which is present in the form of an oxide, this additive being selected from praseodymium, lanthanum and neodymium. It should be observed here that the invention obviously covers the case of compositions comprising a combination of additives. [0014]The additive content does not exceed 50% by weight, the zirconium oxide constituting at least 50% by weight of the composition. This content is expressed as the weight of oxide of the additive or of all the additives in the case of compositions containing several additives, with respect to the weight of the composition as a whole (zirconium oxide plus additive oxide(s)). This additive content may vary in a wide range and more particularly between 5% and 40% and most particularly between 10% and 40%. This content may be quite particularly between 10% and 30%. [0015]According to one variant, the compositions of the invention may further comprise aluminum oxide Al.sub.2O.sub.3. In this case, the aluminum content (Al.sub.2O.sub.3 weight % with respect to the total composition) is generally not more than 20%, and, preferably, is between 1% and 10%. [0016]According to another variant, the compositions of the invention may further comprise silica in proportions identical to those given above for alumina. [0017]The other main feature of the compositions of the invention is their high specific surface area at high temperature. [0018]As stated above, this area is at least 29 m.sup.2/g, after calcination for 10 hours at 1000.degree. C. Under the same calcination conditions, this area may be at least 35 m.sup.2/g, or even at least 40 m.sup.2/g and even more preferably at least 50 m.sup.2/g. Areas of about 60 m.sup.2/g may be reached. [0019]At even higher calcination temperatures, the compositions of the invention preserve high surface areas. Thus, after calcination for 4 hours at 1100.degree. C., these compositions may have a specific surface area of at least 10 m.sup.2/g or even at least 15 m.sup.2/g. Areas of about 20 m.sup.2/g may be obtained. [0020]Furthermore, after calcination for 10 hours at 1200.degree. C., the compositions of the invention may still have a specific surface area of at least 2 m.sup.2/g and more particularly of at least 3 m.sup.2/g. [0021]At lower temperatures than those mentioned above, for example after calcination for 4 hours at 900.degree. C., and according to the variants of the invention, the compositions may have a specific surface area of at least 45 m.sup.2/g, more particularly of at least 50 m.sup.2/g and preferably of at least 55 m.sup.2/g and even more preferably of at least 70 m.sup.2/g. Areas of about 80 m.sup.2/g may be obtained. [0022]The compositions of the invention may in certain cases be in the form of solid solutions of the additive in the zirconium oxide. [0023]In this case, the XR diffraction diagrams of these compositions reveal the existence of a single phase corresponding to that of a zirconium oxide crystallized in the cubic system or in the quadratic system, thereby reflecting the incorporation of the additive in the crystal lattice of the zirconium oxide, and hence the production of a true solid solution. The compositions may also be in the form of a mixture of phases, particularly in the case of high additive contents, that is of at least 40%. [0024]The compositions of the invention also have a specific porosity. They in fact contain mesopores, that is pores between 10 nm and 500 nm in size, even after calcination at high temperature. These size values are obtained by mercury porosimetry (analysis performed with an Autopore 9410 porosimeter, manufactured by Micromeritics, comprising two low pressure stations and one high pressure station). These mesopores may contribute a high proportion of the total pore volume, for example, they may contribute at least 30%, more particularly at least 40% of the total pore volume. Continue reading... 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