Treating catalysts
A method includes contacting a catalyst including a metal having an average particle size of approximately one nanometer or greater with SO 2 ; and reducing the average particle size of the metal.
1. A method, comprising:
contacting a catalyst comprising a metal having an average particle size of approximately one nanometer or greater with SO 2 ; and
reducing the average particle size of the metal or re-dispersing the metal.
2. The method of claim 1 , wherein the metal comprises silver or gold.
3. The method of claim 1 , wherein the catalyst comprises the metal supported on a substrate.
4. The method of claim 3 , wherein the metal has a concentration of at least 0.3 wt %.
5. The method of claim 3 , wherein the metal has a concentration of at least 0.5 wt %.
6. The method of claim 1 , wherein the SO 2 is in a mixture of gases.
7. The method of claim 6 , wherein the SO 2 has a concentration of at least 10 ppm.
8. The method of claim 6 , wherein the SO 2 has a concentration of at least 50 ppm.
9. The method of claim 1 , wherein the catalyst comprises silver and aluminum oxide.
10. The method of claim 9 , wherein the catalyst is contacted with SO 2 at 600° C. or higher.
11. The method of claim 1 , further comprising, prior to contacting the catalyst with SO 2 , heating the catalyst in an environment substantially free of SO 2 .
12. The method of claim 1 , further comprising, prior to contacting the catalyst with SO 2 , heating the catalyst in an environment comprising SO 2 .
13. The method of claim 1 , wherein the catalyst is contacted with SO 2 for at least 0.1 hours.
14. The method of claim 1 , further comprising performing selective catalytic reduction of NO x with the catalyst.
15. The method of claim 1 , further comprising contacting the catalyst with NO x and CH 4 .
16. The method of claim 1 , wherein the average particle size is approximately two nanometers or greater prior to contacting the catalyst with SO 2 .
17. The method of claim 1 , wherein the average particle size is approximately five nanometers or greater prior to contacting the catalyst with SO 2 .
18. The method of claim 1 , wherein the average particle size is approximately 100 nanometers or greater prior to contacting the catalyst with SO 2 .
19. The method of claim 1 , wherein the contacting step is performed in a catalytic reaction that requires the catalyst.
20. The method of claim 1 , further comprising, after the reducing step, catalyzing a reaction using the catalyst containing the metal whose average particle size, remains substantially unchanged or is further reduced.
21. The method of claim 20 , wherein catalyzing the reaction is performed in the presence of SO 2 .
22. The method of claim 1 , further comprising, after the re-dispersing step, catalyzing a reaction using the catalyst in which the catalyst remains dispersed.
23. The method of claim 22 , wherein catalyzing the reaction is performed in the presence of SO 2 .
24. The method of claim 1 , wherein the catalyst comprises gold and iron oxide.
25. The method of claim 24 , wherein the catalyst is contacted with SO 2 at a temperature between 400° C. and 600° C.