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, Jr and Pt.
1 . A catalyst for treating exhaust gas comprising at least one small pore molecular sieve having an KFI 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, Jr and Pt and combinations thereof, based on the total weight of the molecular sieve.
2 . The catalyst of claim 1 , wherein said molecular sieve has silica-to-alumina ratio (SAR) of 2 to 300.
3 . The catalyst of claim 1 , wherein said molecular sieve has an isotype selected from ZK-5, 118-crown-61[Al—Si—O]-KFI, [Zn—Ga,As—O]-KFI, (Cs,K)-ZK-5, P, and Q isotypes.
4 . The catalyst of claim 1 , wherein said molecular sieve is a ZK-5 isotype.
5 . The catalyst of claim 1 , wherein said metal is copper.
6 . The catalyst of claim 1 , wherein said metal is platinum.
7 . The catalyst of claim 1 , wherein said molecular sieve is an aluminosilicate and has an SAR of 8 to 150.
8 . The catalyst of claim 1 , 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 1 , 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 1 , further comprising a metal promoted medium, large, or meso-pore molecular sieve.
11 . The catalyst of claim 1 , further comprising a Cu or Fe promoted molecular sieve having a chabazite framework.
12 . A catalytic washcoat comprising a catalyst according to any of claims 1 , and further comprising at least one binder selected from alumina, silica, non-zeolite silica-alumina, natural clay, TiO 2 , ZrO 2 , and SnO 2 .
13 . A catalytic article comprising a washcoat according to claim 12 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.
14 . A catalytic article comprising an extruded-type flow through honeycomb formed from an extrudate comprising a catalyst according to claim 1 .
15 . The catalytic article of claim 14 further comprising a transition metal promoted zeolite coating.
16 . 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 1 .
17 . The system of claim 16 further comprising a catalyzed soot filter and a diesel oxidation catalyst having a platinum group metal, wherein said diesel oxidation catalyst is disposed upstream of said selective catalytic reduction catalyst.
18 . 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 1 ; and
b. converting at least a portion of said NO to N 2 and/or converting at least a portion of NH 3 to at least one of N 2 and NO 2 .
19 . The method of claim 18 , wherein said exhaust gas contains NOx, a nitrogenous reducing agent, and a ratio of NO to NO 2 from about 4:1 to about 1:3 by volume, and said catalyst is a selective reduction catalyst.
20 . The method of claim 18 , wherein said exhaust gas contains NH 3 and said catalyst is an ammonia slip catalyst.