Ceric oxide and method for production thereof, and catalyst for exhaust gas clarification
The present invention relates to ceric oxide that has excellent heat resistance and oxygen absorbing and desorbing capability useful as a co-catalyst material suitable for a catalyst for purifying exhaust gas, that is capable of maintaining a large specific surface area even in use in a high temperature environment, and that is suitable for use in a high temperature environment, yet capable of exhibiting high oxygen absorbing and desorbing capability also in a lower temperature range, a method for preparing such ceric oxide, and a catalyst for purifying exhaust gas utilizing such ceric oxide. The ceric oxide is an oxide composed essentially of ceric oxide, and has a specific surface area of not smaller than 30.0 m 2 /g after calcination at 900° C. for 5 hours.
1. A ceric oxide which is an oxide consisting essentially of ceric oxide, and has following properties:
said ceric oxide has a specific surface area of not smaller than 30.0 m 2 /g after calcination at 900° C. for 5 hours, and
said ceric oxide has an S1/S2 ratio of not lower than 0.120 taken after calcination at 1000° C. for 5 hours, said S1/S2 ratio is a ratio of an area (S1) defined by a baseline and a TPR curve in a temperature range of 200 to 600° C. to an area (S2) defined by said baseline and said TPR curve in a temperature range of 600 to 1000° C.
2. The ceric oxide of claim 1 , wherein said ceric oxide has OSC of not smaller than 0.60 mlO 2 /g/s at 400° C., after calcination at 900° C. for 5 hours.
3. The ceric oxide of claim 1 , wherein said ceric oxide has a tap density of not higher than 1.3 g/ml, after calcination at 300° C. for 10 hours.
4. The ceric oxide of claim 1 , wherein said ceric oxide has a total pore volume of not smaller than 0.50 ml/g, after calcination at 300° C. for 10 hours.
5. A method for preparing a ceric oxide of claim 1 , comprising the steps of:
(a) providing a cerium solution wherein not less than 90 mol % of the cerium are tetravalent cerium ions, said cerium solution having a cerium concentration of 10 to 60 g/L in terms of cerium oxide;
(b) holding said cerium solution prepared in step (a) at 60 to 220° C. under heating;
(c) cooling said heated cerium solution;
(d) adding a precipitant to said cooled cerium solution to obtain a precipitate; and
(e) calcining said precipitate.
6. The method of claim 5 , wherein said calcining in step (e) is carried out at 250 to 900° C.
7. The method of claim 5 , further comprising, after step (d) and before step (e), step (d1) of heat-treating said precipitate obtained in step (d) in a solvent at 60 to 220° C. to obtain a precipitate.
8. The method of claim 5 , wherein said step (a) comprises:
(a-1) providing an initial cerium solution wherein not less than 90 mol % of the cerium are tetravalent cerium ions, and
(a-2) adjusting a cerium concentration of said initial cerium solution to prepare a cerium solution having a cerium concentration of 10 to 60 g/L in terms of cerium oxide.
9. A catalyst for purifying exhaust gas comprising a co-catalyst, wherein said co-catalyst comprises ceric oxide of claim 1 .