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 catalyst for treating exhaust gas comprising a molecular sieve comprising an ERI framework and containing from 0.01 to 20 weight percent of a metal 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 and combinations thereof, based on the total weight of the molecular sieve.
2 . The catalyst of claim 1 , wherein said molecular sieve comprises a second framework.
3 . The catalyst of claim 2 , wherein said molecular sieve is an aluminosilicate.
4 . The catalyst of claim 2 , wherein said molecular sieve is a ZSM-34 isotype.
5 . The catalyst of claim 4 , wherein said aluminosilicate has an SAR of 2 to 300.
6 . The catalyst of claim 4 , wherein said aluminosilicate has an SAR of 8 to 150.
7 . The catalyst of claim 4 , wherein said transition metal is Cu.
8 . The catalyst of claim 7 , wherein said transition metal is present in an amount of 0.5 to 5 wt. % based on the total weight of the molecular sieve.
9 . The catalyst of claim 8 , wherein said transition metal is added to the zeolite by one of incipient wetness, ion exchange, and during zeolite synthesis.
10 . The catalyst of claim 4 , 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 molecular sieve.
11 . The catalyst of claim 4 , wherein the molecular sieve has an alkali content of about 1 weight percent based on the total weight of the molecular sieve.
12 . The catalyst of claim 4 , further comprising a medium, large, or meso-pore molecular sieve.
13 . The catalyst of claim 4 , further comprising a Cu or Fe promoted molecular sieve having a chabazite framework.
14 . A catalytic washcoat comprising a catalyst according to claim 4 , and further comprising at least one binder selected from alumina, silica, non-zeolite silica-alumina, natural clay, TiO 2 , ZrO 2 , and SnO 2 .
15 . A catalytic article comprising a washcoat according to claim 14 coated on a substrate selected from a metal flow-through substrate, a ceramic flow-through substrate, a wall-flow filter, a sintered metal filter, and a partial filter.
16 . A catalytic article comprising an extruded-type flow through honeycomb formed from an extrudate comprising a catalyst according to claim 4 .
17 . The catalytic article of claim 16 further comprising a transition metal promoted zeolite coating.
18 . A system for treating exhaust gas comprising a selective catalytic reduction (SCR) catalyst upstream of an NH3 oxidation catalyst (AMOX), wherein in at least one of said SCR and AMOX catalysts comprise a catalyst according to claim 4 .
19 . The system of claim 18 further comprising a diesel oxidation catalyst having a platinum group metal upstream of said selective catalytic reduction catalyst.
20 . A method for treating an exhaust gas comprising the steps of:
a. contacting an exhaust gas stream containing NOx and/or NH 3 in the presence of a catalyst according to claim 4 ; and
b. converting at least a portion of said NO x to N 2 and/or converting at least a portion of NH 3 to at least one of N 2 and NO 2 .
21 . The method of claim 20 , wherein said exhaust gas contains NOx and a nitrogenous reducing agent and said catalyst is a selective reduction catalyst.
22 . The method of claim 20 , wherein said exhaust gas contains NH 3 and said catalyst is an ammonia slip catalyst.
23 . The method of claim 20 , wherein said exhaust gas comprises a ratio of NO to NO 2 from about 4:1 to about 1:3 by volume.