Ammonia oxidation catalyst for power utilities
The present invention is directed to a method for removal by oxidation of the excess ammonia (NH 3 ) gas (“ammonia slip”) resulting from flue gases that have been subjected to selective catalytic reduction (SCR) for reduction of nitrogen oxides (NOx) with ammonia. More specifically, the inventive method uses an ammonia oxidation catalyst consisting of a zeolite, one or more precious metals, and a base metal compound, to catalyze the oxidation of both ammonia and carbon monoxide (CO), while minimizing the formation of nitrogen oxides (NOx). The present invention is useful in treating flue and exhaust gases.
1. A method for treating the flue gas stream generated by a stationary combustion source equipped with a selective catalytic reduction (SCR) system and for selectively oxidizing unreacted ammonia to nitrogen, said method comprising:
(a) contacting said flue gas stream containing said unreacted ammonia with an ammonia oxidation catalyst in the presence of an oxidant, wherein said ammonia oxidation catalyst comprises a zeolite, a precious metal and a base metal compound; and
(b) thereby oxidizing said unreacted ammonia to nitrogen.
2. The method of claim 1 , wherein said ammonia oxidation catalyst is located downstream from said selective catalytic reduction system.
3. The method of claim 1 , wherein said ammonia oxidation catalyst is added to said selective catalytic reduction system.
4. The method of claim 1 , wherein said precious metal is selected from the group consisting of platinum, palladium, rhodium and gold.
5. The method of claim 4 , wherein said precious metal is platinum.
6. The method of claim 1 , wherein said precious metal loading is from about 0.1 to about 100 g/ft 3 .
7. The method of claim 1 , wherein said precious metal content is from about 0.02 wt. % to about 0.20 wt. % of the total weight of said zeolite.
8. The method of claim 1 , wherein said base metal compound is from about 2 wt. % to about 20 wt. % of the total weight of said zeolite.
9. The method of claim 1 , wherein said base metal compound is selected from the group consisting of copper, vanadium, manganese, zinc, zirconium, and molybdenum metal compounds.
10. The method of claim 9 , wherein said base metal compound is a base metal-oxygen complex.
11. The method of claim 1 , wherein said zeolite is selected from the group consisting of mordenite, ferrierite, zeolite Y, ZSM-5, and beta zeolites.
12. The method of claim 1 , wherein said ammonia oxidation catalyst further comprises one or more rare earth metals.
13. The method of claim 1 , wherein said treated flue gas is contacted with the ammonia oxidation catalyst at temperatures from about 200° to about 450° C.
14. The method of claim 1 , wherein said ammonia oxidation catalyst is applied onto a substrate in the form of a honeycomb.
15. The method of claim 1 , wherein a source of oxygen is added to said flue gas stream prior to contact with said ammonia oxidation catalyst.
16. The method of claim 1 , wherein said flue gases are obtained from the combustion of coal.
17. The method of claim 1 , wherein said flue gases are obtained from the combustion of natural gas.
18. The method of claim 1 , wherein said flue gases are obtained from the combustion of oil.