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

Patent metadata

Field	Value
Publication number	US-11040332-B2
Application number	US-201214119264-A
Country	US
Kind code	B2
Filing date	May 28, 2012
Priority date	Jun 1, 2011
Publication date	Jun 22, 2021
Grant date	Jun 22, 2021

Abstract

Provided are: a complex oxide that exhibits high redox ability even at low temperatures, has excellent heat resistance, and stably retains these characteristics even on repeated oxidation and reduction at high temperature; a method for producing the same; and an exhaust gas purification catalyst. The inventive complex oxide contains more than 0 but no more than 20 parts by mass of Si, calculated as SiO2, per total 100 parts by mass of rare earth metal elements including Ce, calculated as oxides; and has a characteristic such that when it is subjected to temperature-programmed reduction (TPR) measurement in a 10% hydrogen-90% argon atmosphere at from 50° C. to 900° C. with the temperature increasing at a rate of 10° C./min, followed by oxidation treatment at 500° C. for 0.5 hours, and then temperature-programmed reduction measurement is performed again, its calculated reduction rate at and below 400° C. is at least 1.5%.

First claim

The invention claimed is:

1. A complex oxide comprising:
cerium oxide;
an oxide of a rare earth metal element other than cerium, wherein the mass ratio of cerium to rare earth metal elements other than cerium is between 85:15 and 99:1, calculated as oxides; and
silicon oxide in an amount of more than 0 parts by mass but no more than 20 parts by mass, calculated as SiO 2 , per total 100 parts by mass of rare earth metal elements including cerium, calculated as oxides;
wherein the complex oxide has, subsequent to temperature-programmed reduction treatment in a 10% hydrogen-90% argon atmosphere between 50° C. and 900° C. with temperature increasing at 10° C/min, followed by oxidation treatment at 500° C. for 0.5 hours, a calculated reduction rate at and below 400° C. of at least 1.5% as measured by temperature-programmed reduction (TPR) in a 10% hydrogen-90% argon atmosphere between 50° C. and 900° C. with temperature increasing at 10° C/min; and
wherein the complex oxide has, subsequent to three repetitions of reduction treatment in a 10% hydrogen-90% argon atmosphere between 50° C. and 900° C. with temperature increasing at 10° C/min, followed by oxidation treatment at 500° C. for 0.5 hours, a specific surface area according to the BET method of at least 20 m 2 /g.

2. The complex oxide claimed in claim 1 , containing 2-20 parts by mass of silicon, calculated as SiO 2 , per total 100 parts by mass of rare earth metal elements including cerium, calculated as oxides.

3. The complex oxide claimed in claim 1 , where said reduction rate at and below 400° C. is at least 2.0%.

4. The complex oxide claimed in claim 1 , where said specific surface area according to the BET method is at least 25 m 2 /g.

5. A method for producing complex oxide of claim 1 , the method comprising:
heating a cerium solution wherein at least 90 mol % of cerium ions are tetravalent such that the temperature is maintained above 60° C. to form a cerium suspension;
adding precipitant to the cerium suspension to form a precipitate;
calcining the precipitate to obtain an oxide;
impregnating the oxide with a silicon oxide precursor solution to form an impregnated oxide;
firing the impregnated oxide to form a fired substance;
reducing the fired substance to form a reduced substance; and
oxidizing the reduced substance to form the complex oxide.

6. The method claimed by claim 5 , further comprising:
adding at least one precursor of an oxide of a rare earth metal element other than cerium to the cerium suspension; and
heating the cerium suspension containing the precursor of oxide of rare earth metal element other than cerium, such that the temperature is maintained above 100° C.; prior to
adding the precipitant to the cerium suspension.

7. A method for producing complex oxide of claim 1 , the method comprising:
heating a cerium solution wherein at least 90 mol % of cerium ions are tetravalent such that the temperature is maintained above 60° C. to form a cerium suspensions:
adding at least one silicon oxide precursor to the cerium suspension;
heating the cerium suspension containing the silicon oxide precursor such that the temperature is maintained above 100° C.;
adding precipitant to the cerium suspension containing silicon oxide precursor to form a precipitate;
firing the precipitate to form a fired substance;
reducing the fired substance to form a reduced substance; and
oxidizing the reduced substance to form the complex oxide.

8. The method claimed by claim 7 , further comprising:
heating a cerium solution wherein at least 90 mol % of cerium ions are tetravalent such that the temperature is maintained above 60° C. to form a cerium suspension;
adding at least one precursor of an oxide of a rare earth metal element other than cerium to the cerium suspension;
heating the cerium suspension containing the silicon oxide precursor and the precursor of oxide of rare earth metal element other than cerium, such that the temperature is maintained above 100° C.;
adding precipitant to the heated suspension to form a precipitate;
firing the precipitate to form a fired substance;
reducing the fired substance to form a reduced substance; and
oxidizing the reduced substance to form the complex oxide.

9. The method claimed in claim 5 , where the cerium concentration in the cerium solution is 5-100 g/L, calculated as CeO 2 .

10. The method claimed in claim 5 , wherein the reduction is performed at 150-500° C., or wherein the oxidation is performed at 200-800° C., or both.

11. The method claimed in claim 6 , wherein the precursor of an oxide of a rare earth metal element other than cerium comprises at least one element selected from yttrium, lanthanum, praseodymium, and neodymium.

12. The method claimed in claim 7 , wherein the cerium concentration in the cerium solution is 5-100 g/L, calculated as CeO 2 .

13. The method claimed in claim 7 , wherein the reduction is performed at 150-500° C., or wherein the oxidation is performed at 200-800° C., or both.

14. The method claimed in claim 8 , wherein the precursor of an oxide of a rare earth metal element other than cerium comprises at least one element selected from yttrium, lanthanum, praseodymium, and neodymium.

15. The complex oxide claimed in claim 1 , wherein the rare earth metal element other than cerium comprises at least one element selected from yttrium, lanthanum, praseodymium, and neodymium.

16. An exhaust gas purification catalyst comprising the complex oxide claimed in claim 1 .

17. An exhaust gas purification catalyst comprising the complex oxide claimed in claim 15 .

Assignees

• Ohtake Naotaka
• MITSUOKA Keiichiro
• Yokota Kazuhiko
• Rhodia Operations

Inventors

• Ohtake Naotaka
• MITSUOKA Keiichiro
• Yokota Kazuhiko

Classifications

• B01J23/10 Primary

  of rare earths · CPC title

• F01N3/10

  by thermal or catalytic conversion of noxious components of exhaust · CPC title

• B01D53/86

  Catalytic processes · CPC title

• C01P2002/50

  Solid solutions · CPC title

• C01P2006/13

  thermal stability thereof at high temperatures · CPC title