Compositions based on cerium oxide, zirconium oxide and, optionally, another rare earth oxide, having a specific raised surface at 1100°c, method for the production and use thereof as a catalyst

Abstract

The inventive composition, according to a first embodiment, consists essentially of a cerium oxide and a zirconium oxide in an atomic ratio Ce/Zr of at least 1. According to a second embodiment, said composition is based on cerium oxide, zirconium oxide with an atomic ratio Ce/Zr of at least 1 and at least one rare earth oxide other than cerium. After calcination at 1100 C., said composition has a specific surface of at least 9 m2/g in the first embodiment and at least 19 m2/g in the second embodiment. The inventive composition can be used as a catalyst especially for the treatment of waste gases from internal combustion engines.

1 - 13 . (canceled)  
   
   
       14 . A composition essentially consisting of a cerium oxide and a zirconium oxide in a Ce/Zr atomic ratio of at least 1, said composition having a specific surface area of at least 9 m 2 /g after calcination at 1100° C. for 4 hours.  
   
   
       15 . The composition as claimed in  claim 14 , having a specific surface area of at least 15 m 2 /g after calcination at 1100° C. for 4 hours.  
   
   
       16 . The composition as claimed in  claim 14 , having a specific surface area of at least 2 m 2 /g, optionally at least 4 m 2 /g, after calcination at 1200° C. for 4 hours.  
   
   
       17 . A composition based on a cerium oxide, a zirconium oxide in a Ce/Zr atomic ratio of at least 1 and at least one oxide of a rare earth other than cerium, having a specific surface area of at least 19 m 2 /g after calcination at 1100° C. for 4 hours.  
   
   
       18 . The composition as claimed in  claim 16 , wherein the specific surface area is of at least 3 m 2 /g, optionally at least 6 m 2 /g.  
   
   
       19 . The composition as claimed in  claim 17 , further comprising at least one oxide of a rare earth other than cerium, selected from the group consisting of lanthanum, neodymium and praseodymium.  
   
   
       20 . The composition as claimed in  claim 19 , wherein the oxide of a rare earth other than cerium is present in the composition in an amount of at least 20% by weight.  
   
   
       21 . A method of preparing a composition as claimed in  claim 14 , comprising the steps of: 
 (a) forming a mixture comprising a cerium compound, a zirconium compound and, optionally, a compound of a rare earth other than cerium, selected from the group consisting of lanthanum, neodymium and praseodymium;    (b) bringing said mixture into contact with a basic compound, to obtain a precipitate;    (c) heating said precipitate in an aqueous medium;    (d) adding an additive, selected from the group consisting of anionic surfactants, nonionic surfactants, polyethylene glycols, carboxylic acids, the salts of carboxylic acids, and carboxymethylated fatty alcohol ethoxylate surfactants, to the precipitate obtained in the previous step; and, then    (e) calcining the precipitate obtained in step (d).    
   
   
       22 . The method as claimed in  claim 21 , wherein, the zirconium compound, cerium compound and compound of the rare earth, is selected from the group consisting of nitrates, acetates, chlorides and ceric ammonium nitrates.  
   
   
       23 . The method as claimed in  claim 21 , wherein, in the mixture of step (a), a the cerium compound is in the Ce(III) form and an oxidizing agent is added during step (a) or during step (b), optionally at the end of the latter step.  
   
   
       24 . The method as claimed in  claim 21 , wherein the precipitate is heated in step (c) to a temperature of at least 100° C.  
   
   
       25 . A catalytic system, comprising a composition as claimed in  claim 14 .  
   
   
       26 . A method of automobile postcombustion catalysis of exhaust gases of an internal combustion engine, said method comprising the step of treating said exhaust gases with a catalytic system as claimed in  claim 25.