Method for selective catalytic reduction of nitrogen oxides
View Patent ↗A method for catalytically reducing nitrogen oxide compounds (NO x , defined as nitric oxide, NO, +nitrogen dioxide, NO 2 ) in a gas by a material comprising a base metal consisting essentially of CuO and Mn, and oxides of Mn, on an activated metal hydrous metal oxide support, such as HMO:Si. A promoter, such as tungsten oxide or molybdenum oxide, can be added and has been shown to increase conversion efficiency. This method provides good conversion of NO x to N 2 , good selectivity, good durability, resistance to SO 2 aging and low toxicity compared with methods utilizing vanadia-based catalysts.
1. A method for catalytically reducing nitrogen oxide compounds, comprising exposing a gas comprising nitrogen oxides, consisting of NO and NO 2 , in the presence of NH 3 to a catalyst comprising an active component selected from CuO, Mn, and oxides of Mn on a hydrous metal oxide support.
2. The method of claim 1 wherein the catalyst further comprises a promoter component selected from WO 3 and MoO 3 .
3. The method of claim 2 wherein the promoter concentration is less than approximately 5% by weight of the catalyst.
4. The method of claim 1 wherein the hydrous metal oxide support further includes silica.
5. The method of claim 4 wherein the silica concentration comprises an amount effective to thermally stabilize the catalyst for temperatures up to 1000° C.
6. The method of claim 1 wherein the nitrogen oxide have a concentration less than approximately 1000 parts per million.
7. The method of claim 1 where in the gas further comprises compounds selected from sulfur oxides, water vapor, oxygen, carbon dioxide, carbon monoxide and hydrogen.
8. The method of claim 1 wherein the presence of NH 3 occurs from the thermal decomposition of urea.
9. The method of claim 1 wherein the method for catalytically reducing nitrogen oxide compounds occurs at a temperature greater than approximately 100° C.
10. The method of claim 1 wherein the method for catalytically reducing nitrogen oxide compounds occurs at a temperature les than approximately 750° C.
11. The method of claim 1 wherein the activated meta hydrous metal oxide support is selected from a hydrous titanium oxide and a hydrous zirconium oxide.
12. The method of claim 1 wherein the catalytic reduction of the nitrogen oxides has a conversion efficiency to nitrogen of greater than 90 percent.
13. The method of claim 1 wherein the NH 3 concentration is approximately equal to the nitrogen oxides concentration.
14. The method of claim 1 wherein the oxides of Mn are selected from MnO, MnO 2 , and MnO 1.5 .
15. The method of claim 1 wherein the catalyst is applied to a ceramic rate.
16. The method of claim 15 wherein the ceramic substrate is selected from a bead, a pellet, or a monolith.
17. The method of claim 16 wherein the monolith is a cordierite honeycomb monolith.