Catalyst/catalyst support compositions having high reducibility and comprising a nanometric cerium oxide deposited onto a support substrate

Abstract

Catalyst/catalyst support compositions are characterized by a supported cerium oxide, deposited onto a silica, alumina, titanium or zirconium based support, including particles of said supported oxide deposited onto said support, individualized or in the form of aggregates, no greater than 500 nm in size and having, after 6 hours of calcination at a temperature of at least 800° C., a measured reducibility from 30° C. and 900° C. of at least 80%; such compositions are prepared by combining a colloidal dispersion of the supported oxide and a suspension of the support, drying the resulting mixture by atomization and drying the resulting product by calcination.

1 .- 23 . (canceled) 
   
   
       24 . A catalyst/catalyst support composition comprising a supported oxide, based on a cerium oxide, deposited onto a support based on silica, alumina, titanium oxide or zirconium oxide, which comprises particles of said supported oxide deposited onto said support, said particles being separate or in the form of aggregates, having a size of at most 500 nm, and which exhibits, after calcination at a temperature of at least 800° C. for 6 hours, a reducibility measured from 30° C. to 900° C. of at least 80%. 
   
   
       25 . A catalyst/catalyst support composition comprising a supported oxide, based on a cerium oxide, deposited onto an alumina-based support, which comprises particles of said supported oxide deposited onto said support, said particles being separate or in the form of aggregates, having a size of at most 500 nm, and which exhibits, after calcination at a temperature of at least 800° C. for 6 hours, a reducibility measured from 30° C. to 900° C. of at least 80%, the alumina support of which additionally being devoid of the elements barium and strontium. 
   
   
       26 . A catalyst/catalyst support composition as defined by  claim 24 , wherein the supported oxide comprises a mixture of a cerium oxide and at least one oxide of another element M selected from among zirconium and the rare earth metals other than cerium. 
   
   
       27 . The catalyst/catalyst support composition as defined by  claim 24 , wherein said particles, separate or in the form of aggregates thereof, have a size of at most 50 nm. 
   
   
       28 . The catalyst/catalyst support composition as defined by  claim 24 , wherein said particles, separate or in the form of aggregates thereof, have a size of at most 10 nm. 
   
   
       29 . The catalyst/catalyst support composition as defined by  claim 24 , exhibiting a reducibility of at least 85%. 
   
   
       30 . The catalyst/catalyst support composition as defined by  claim 24 , wherein the supported oxide comprises cerium oxide or a mixture of a cerium oxide and of a zirconium oxide, and, optionally, an oxide of a rare earth metal other than cerium, and having a zirconium content such that the Ce/Zr atomic ratio is at least 1, and in that it exhibits, after calcination at a temperature of at least 800° C. for 6 hours, a reducibility, measured from 30° C. to 600° C., of at least 35%. 
   
   
       31 . The catalyst/catalyst support composition as defined by  claim 24 , wherein the support essentially consists of alumina or alumina stabilized by at least one element selected from among the rare earth metals, silicon and zirconium. 
   
   
       32 . The catalyst/catalyst support composition as defined by  claim 24 , wherein the supported oxide comprises a mixture of a cerium oxide, of a zirconium oxide and of an oxide of a rare earth metal other than cerium and wherein the support is based on alumina stabilized by an element selected from the group consisting of barium, strontium and lanthanum. 
   
   
       33 . The catalyst/catalyst support composition as defined by  claim 24 , wherein the supported oxide comprises a mixture of a cerium oxide, of a praseodymium oxide and of an oxide of a rare earth metal other than cerium and praseodymium and wherein the support is based on alumina stabilized by an element selected from the group consisting of barium, strontium and lanthanum. 
   
   
       34 . The catalyst/catalyst support composition as defined by  claim 24 , wherein it exhibits a proportion of supported oxide of at most 75% by weight. 
   
   
       35 . A process for the preparation of a catalyst/catalyst support composition as defined by  claim 24 , which comprises the following stages:
 (a) admixing a colloidal dispersion of the supported oxide and, if appropriate, of the oxide of the element M and a suspension of the support;   (b) drying the mixture thus formed by atomization; and   (c) calcining the dried product thus obtained.   
   
   
       36 . The process as defined by  claim 35 , wherein the colloidal dispersion of the supported oxide additionally comprises an amino acid. 
   
   
       37 . A process for the preparation of a catalyst/catalyst support composition as defined by  claim 24 , which comprises the following stages:
 (a) providing a liquid mixture comprising a salt of cerium and, if appropriate, of the element M and a suspension of the support;   (b) heating the mixture thus formed at a temperature of at least 100° C.;   (c) recovering the precipitate thus obtained; and   (d) calcining said precipitate.   
   
   
       38 . A process for the preparation of a catalyst/catalyst support composition as defined by  claim 24 , wherein the support comprises alumina stabilized by a stabilizing element selected from among the rare earth metals, barium and strontium, which comprises the following stages:
 (a) providing a liquid mixture comprising a colloidal dispersion of the supported oxide and, if appropriate, of the oxide of the element M, an aluminum compound and a compound of the stabilizing element;   (b) mixing the mixture thus provided and a base, whereby a suspension comprising a precipitate is obtained;   (c) drying the suspension thus obtained; and   (d) calcining the dried product thus obtained.   
   
   
       39 . A process for the preparation of a catalyst/catalyst support composition as defined by  claim 24 , wherein the support comprises alumina stabilized by a stabilizing element selected from among the rare earth metals, barium and strontium, which comprises the following stages:
 (a) providing a liquid mixture comprising a colloidal dispersion of the supported oxide and, if appropriate, of the oxide of the element M and an aluminum compound;   (b) mixing the mixture thus provided and a base, whereby a suspension comprising a precipitate is obtained;   (c) adding a compound of a stabilizing element to the suspension thus obtained;   (d) drying the suspension resulting from the preceding stage (c); and   (e) calcining the dried product thus obtained.   
   
   
       40 . The process as defined by  claim 38 , wherein the suspension resulting from stage (b) is subjected to a maturing before stage (c). 
   
   
       41 . The process as defined by  claim 38 , wherein the suspension is dried by atomization. 
   
   
       42 . The process as defined by  claim 38 , wherein before the drying stage, the precipitate is separated from the suspension, washed and redispersed in water to form another suspension. 
   
   
       43 . The process as defined by  claim 38 , wherein the compound of the stabilizing element is a salt thereof. 
   
   
       44 . A catalytic system which comprises a catalyst/catalyst support composition as defined by  claim 24 . 
   
   
       45 . In a process for the catalytic treatment of exhaust gases emanating from an internal combustion engine, the improvement which comprises, as the catalyst/catalyst support therefor, the composition as defined by  claim 24 . 
   
   
       46 . The process as defined by  claim 45 , said treatment including a NOx trap.