Complex oxide, method for producing same, and exhaust gas purifying catalyst

Abstract

Disclosed are a composite oxide which is capable of maintaining a large volume of pores even used in a high temperature environment, and which has excellent heat resistance and catalytic activity, as well as a method for producing the composite oxide and a catalyst for exhaust gas purification employing the composite oxide. The composite oxide contains cerium and at least one element selected from aluminum, silicon, or rare earth metals other than cerium and including yttrium, at a mass ratio of 85:15 to 99:1 in terms oxides, and has a property of exhibiting a not less than 0.30 cm 3 /g, preferably not less than 0.40 cm 3 /g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours, and is suitable for a co-catalyst in a catalyst for vehicle exhaust gas purification.

1 . A composite oxide comprising (A) cerium and (B) at least one element selected from the group consisting of aluminum, silicon, and rare earth metals other than cerium,
 wherein a mass ratio of (A):(B) in the composite oxide is 85:15 to 99:1 in terms oxides, and   wherein the composite oxide has a property of exhibiting a not less than 0.30 cm 3 /g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours.   
     
     
         2 . The composite oxide according to  claim 1 , having a property of exhibiting a not less than 0.40 cm 3 /g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours. 
     
     
         3 . The composite oxide according to  claim 1 , having a property of exhibiting a not less than 0.50 cm 3 /g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours. 
     
     
         4 . The composite oxide according to  claim 1 , having a property of exhibiting a not less than 0.32 cm 3 /g volume of pores with a diameter of not larger than 200 nm, after calcination at 800° C. for 5 hours. 
     
     
         5 . The composite oxide according to  claim 1 , comprising at least silicon as (B), and having a property of exhibiting a not less than 0.60 cm 3 /g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours. 
     
     
         6 . The composite oxide according to  claim 1 , comprising at least one element selected from the group consisting of yttrium, lanthanum, praseodymium, and neodymium as (B). 
     
     
         7 . A catalyst for exhaust gas purification comprising the composite oxide according to  claim 1 . 
     
     
         8 . The composite oxide according to  claim 1 , obtained by a method containing the steps of:
 (e) neutralizing a suspension containing (A) and (B),   (f) adding a surfactant to the suspension neutralized in step (e), followed by a retention time of 10 minutes to 6 hours to obtain a precipitate, without subjecting the suspension to washing between step (e) and step (f), and   (g) calcining the precipitate.   
     
     
         9 . The composite oxide according to  claim 8 , wherein the suspension used in step (e) is obtained by the steps of:
 (a) providing a cerium solution not less than 90 mol % of which cerium ions are tetravalent,   (b) heating and maintaining the cerium solution obtained from step (a) up to and at not lower than 60° C.,   (c) adding an oxide precursor of (B) to a cerium suspension obtained through the heating and maintaining, and   (d) heating and maintaining the cerium suspension containing the oxide precursor of (B) up to and at not lower than 100° C.   
     
     
         10 . The composite oxide according to  claim 9 , wherein a cerium content of the cerium solution in step (a) is 5 to 80 g/L in terms of CeO 2 . 
     
     
         11 . The composite oxide according to  claim 1 , consisting of (A) cerium, (B) at least one element selected from the group consisting of silicon and rare earth metals other than cerium, and (C) oxygen. 
     
     
         12 . The composite oxide according to  claim 11 , consisting of (A) cerium, (B) at least one element selected from the group consisting of silicon, yttrium, lanthanum, praseodymium, and neodymium, and (C) oxygen. 
     
     
         13 . The composite oxide according to  claim 12 , consisting of (A) cerium, (B) at least one element selected from the group consisting of silicon, lanthanum, and praseodymium, and (C) oxygen. 
     
     
         14 . The composite oxide according to  claim 13 , consisting of (A) cerium, (B) silicon, and (C) oxygen.