Non-PGM ammonia slip catalyst
An ammonia slip catalyst having an SCR catalyst and an oxidation catalyst comprising at least two metals, each of which is selected from a specific group, and a substrate upon which at least oxidation catalyst is located is described. The ammonia slip catalyst can have dual layers, with one of the layers containing an SCR catalyst, a second layer containing the oxidation catalyst with comprises at least two metals, each of which is selected from a specific group, and the ammonia slip catalyst does not contain a platinum group metal. Methods of making and using the ammonia slip catalyst to reduce ammonia slip are described.
1. A dual layer ammonia slip catalyst comprising an SCR layer and an oxidation layer, wherein at least the oxidation layer is positioned proximal to a substrate, wherein
the SCR layer comprises a molecular sieve or a vanadium/titania SCR catalyst; and
the oxidation layer consists of:
(a) an ammonia oxidation catalyst consisting of copper and manganese; and
(b) an oxide support material consisting of alumina and either a CeO 2 /ZrO 2 mixed oxide or a Zr-stabilized CeO 2 mixed oxide;
wherein the ammonia slip catalyst does not comprise a platinum group metal.
2. The dual layer ammonia slip catalyst of claim 1 , wherein the oxidation layer further comprises an oxide support material comprising one or both of alumina and silica.
3. A method for reducing the concentration of ammonia in a flue gas stream generated by a combustion source, the method comprising contacting a flue gas stream containing ammonia with a dual layer ammonia slip catalyst of claim 1 .
4. The dual layer ammonia slip catalyst of claim 1 , wherein the substrate is a flow-through substrate.
5. The dual layer ammonia slip catalyst of claim 1 , wherein the Zr-stabilized CeO 2 mixed oxide comprises Ce and Zr present in about a 1:1 mole ratio.
6. The dual layer ammonia slip catalyst of claim 1 , wherein the oxide support material comprises about 20 mole % La-stabilized Al 2 O 3 and about 80 mole % Zr-stabilized CeO 2 .
7. The dual layer ammonia slip catalyst of claim 1 , wherein the molecular sieve is selected from the group consisting of MOR (mordenite), FER (ferrierite), FAU (zeolite Y), MFI (ZSM-5), BEA (beta zeolites), Fe-BEA, CHA (Chabazite), Cu-CHA and a silicoaluminophosphate comprising a structurally similar framework.
8. The dual layer ammonia slip catalyst of claim 7 , wherein the SCR layer comprises a Fe-BEA or a Cu-CHA zeolite catalyst or a silicoaluminophosphate comprising a structurally similar framework.
9. The dual layer ammonia slip catalyst of claim 8 , wherein the SCR layer comprises a Fe-BEA or a Cu-CHA zeolite or a silicoaluminophosphate comprising a structurally similar framework catalyst and the oxidation layer comprises Cu and Mn.
10. The dual layer ammonia slip catalyst of claim 1 , wherein the catalyst in the oxidation layer is present at a concentration of 0.3 to 1.5 g per in 3 , based on the total weight of metal in the catalyst.
11. The dual layer ammonia slip catalyst of claim 1 , wherein the catalyst in the SCR layer is present at a concentration of 0.5 to 2.5 g per in 3 , based on the total weight of metal in the catalyst.
12. The dual layer ammonia slip catalyst of claim 1 , wherein the ratio of the amount of catalyst in the SCR layer (in g per in 3 ) to the amount of catalyst in the oxidation layer (in g per in 3 ) is between 0.3 and 8.3, based on the total weight of metal in each layer of the catalyst.
13. The dual layer ammonia slip catalyst of claim 1 , wherein the SCR layer is positioned as an overlayer over the oxidation layer or the oxidation layer is located sequential to the SCR layer.