TRANSITION METAL/ZEOLITE SCR CATALYSTS
A method of converting nitrogen oxides in a gas to nitrogen by contacting the nitrogen oxides with a nitrogenous reducing agent in the presence of a zeolite catalyst containing at least one transition metal, wherein the zeolite is a small pore zeolite containing a maximum ring size of eight tetrahedral atoms, wherein the at least one transition metal is selected from the group consisting of Cr, Mn, Fe, Co, Ce, Ni, Cu, Zn, Ga, Mo, Ru, Rh, Pd, Ag, In, Sn, Re, Ir and Pt.
1 . A catalytic article comprising:
a. catalyst for treating exhaust gas comprising a small pore molecular sieve comprising an ERI framework and containing from 0.01 to 20 weight percent Cu based on the total weight of the zeolite, wherein said zeolite comprises a second framework and wherein said molecular sieve is an aluminosilicate, wherein the catalyst is effective to promote the reaction of NH 3 to form nitrogen and water, selectively; and
b. a substrate selected from a flow-through substrate or a wall-flow filter,
wherein the catalyst is coated on the flow-through substrate or a wall-flow filter or is extruded as part of the flow-through substrate or a wall-flow filter.
2 . The catalytic article of claim 1 , wherein said aluminosilicate is a ZSM-34 isotype.
3 . The catalytic article of claim 2 , wherein said aluminosilicate has an SAR of 2 to 300.
4 . The catalytic article of claim 2 , wherein said aluminosilicate has an SAR of 8 to 150.
5 . The catalytic article of claim 2 , wherein said copper is present in an amount of 0.5 to 5 wt. % based on the total weight of the zeolite.
6 . The catalytic article of claim 5 , wherein said copper is added to the zeolite by one of incipient wetness, ion exchange, and during zeolite synthesis.
7 . The catalytic article of claim 2 , wherein the molecular sieve has an alkali content of about 0.7 to about 1.5 weight percent based on the total weight of the zeolite.
8 . The catalytic article of claim 2 , wherein the molecular sieve has an alkali content of about 1 weight percent based on the total weight of the zeolite.
9 . The catalytic article of claim 2 , wherein the catalyst further comprises a medium, large, or meso-pore zeolite.
10 . The catalytic article of claim 2 , wherein the catalyst further comprises a Cu or Fe promoted zeolite having a chabazite framework.
11 . The catalytic article of claim 2 , wherein the catalyst is coating on the substrate.
12 . The catalytic article of claim 11 , wherein the coating further comprises at least one binder selected from alumina, silica, non-zeolite silica-alumina, natural clay, TiO2, ZrO2, and SnO2.
13 . The catalytic article of claim 11 , wherein the substrate is a flow-through substrate.
14 . The catalytic article of claim 11 , wherein the substrate is a wall-flow filter.
15 . The catalytic article of claim 2 , wherein the substrate is formed from an extrudate comprising the catalyst.