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A process is described that removes by oxidation the excess ammonia (NH3) gas from flue gases that have been subjected to selective catalytic reduction (SCR) of oxides of nitrogen (NOx) by ammonia injection. The inventive process incorporates a secondary catalyst of precious metal and vanadia on a m

A process is described that removes by oxidation the excess ammonia (NH3) gas from flue gases that have been subjected to selective catalytic reduction (SCR) of oxides of nitrogen (NOx) by ammonia injection. The inventive process incorporates a secondary catalyst of precious metal and vanadia on a metal oxide such as titania to catalyze the oxidation of both ammonia and carbon monoxide (CO) while maintaining sulfur dioxide (SO2) levels.

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What is claimed is: 1. A method of removing ammonia in flue gases, where ammonia is used as a selective catalytic reduction agent with a primary catalyst for reducing oxides of nitrogen, which comprises the steps of: a. adding ammonia to flue gases and reducing oxides of nitrogen in the presence of

What is claimed is: 1. A method of removing ammonia in flue gases, where ammonia is used as a selective catalytic reduction agent with a primary catalyst for reducing oxides of nitrogen, which comprises the steps of: a. adding ammonia to flue gases and reducing oxides of nitrogen in the presence of said primary catalyst to produce a treated flue gas having a NOx content less than said flue gases and containing unreacted ammonia; b. contacting said treated flue gas with a secondary ammonia oxidation catalyst to reduce the amount of ammonia, said secondary catalyst comprising a precious metal and vanadia on a titania alumina, silica, alumina-silica, zirconia, magnesium oxide, hafnium oxide, or a lanthanum oxide support. 2. The method of claim 1, wherein said support is titania. 3. The method of claim 1, wherein said precious metal is selected from the group consisting of platinum, palladium, rhodium and gold. 4. The method of claim 1, wherein said precious metal is platinum. 5. The method of claim 1, wherein said secondary catalyst is applied onto a substrate in the form of a honeycomb. 6. The method of claim 1, wherein said treated flue gas is contacted with the secondary catalyst at temperatures from about 300�� C. to about 450�� C. 7. The method of claim 1, wherein a source of oxygen is added to said treated flue gas prior to contact with said secondary catalyst. 8. The method of claim 5, wherein said secondary catalyst is present in a range of about 1.0 gram to about 2.5 grams per cubic inch of said substrate. 9. The method of claim 1, wherein said primary catalyst is vanadia and, optionally, tungsten oxide on titania. 10. The method of claim 9, wherein said primary catalyst is a homogeneous extrudate. 11. The method of claim 1, wherein said flue gases are obtained from the combustion of coal. 12. The method of claim 2, wherein said precious metal is platinum. 13. The method of claim 2, wherein said secondary catalyst is applied onto a substrate in the form of a honeycomb. 14. The method of claim 2, wherein said treated flue gas is contacted with the secondary catalyst at temperatures from about 300�� C. to about 450�� C. 15. The method of claim 2, wherein a source of oxygen is added to said treated flue gas prior to contact with said secondary catalst. 16. The method of claim 13, wherein said secondary catalyst is present in a range of about 1.0 gram to about 2.5 grams per cubic inch of said substrate. 17. The method of claim 1, wherein said precious metal is present in amounts of about 0.1 to 2.0 wt. % relative to said support. 18. The method of claim 1, wherein said vanadia comprises from about 1.0 to 10 wt. % of said support. 19. The method of claim 16, wherein said precious metal is present in amounts of about 0.1 to 2.0 wt. % of said titania. 20. The method of claim 19, wherein said vanadia is present in amounts of about 1.0 to 10 wt. % of said titania.