Combined NOx absorber and SCR catalyst
The present invention is directed to selective catalytic reduction catalysts that combine SCR activity with NOx absorber activity. In particular, the disclosed catalytic article includes a substrate having a first and a second material disposed thereon, wherein the first material includes a selective catalytic reduction (SCR) catalyst composition and the second material includes a nitrogen oxides (NOx) absorber composition, wherein the NOx absorber composition does not substantially oxidize ammonia, and wherein the catalytic article is effective to abate NOx from an engine exhaust gas stream. Emission treatment systems for treating an exhaust gas including a catalytic article of the invention are provided, particularly systems that include an injector adapted for the addition of ammonia to the exhaust gas stream located upstream of the catalytic article.
1. A catalytic article comprising:
a substrate having both a selective catalytic reduction (SCR) catalyst composition and a nitrogen oxides (NOx) absorber composition disposed thereon;
wherein:
the NOx absorber composition comprises an alkaline earth metal component; and
the SCR catalyst composition comprises a mixed metal oxide component that is selected from the group consisting of FeTiO 3 , FeAl 2 O 3 , MgTiO 3 , MgAlO 3 , MnOx/TiO 2 , CuTiO 3 , CeZrO 2 , TiZrO 2 , V 2 O 5 /TiO 2 , and mixtures thereof.
2. The catalytic article of claim 1 , wherein the SCR catalyst composition and the NOx absorber composition are mixed in a single layer on the substrate.
3. The catalytic article of claim 1 , wherein the SCR catalyst composition is in a first layer and the NOx absorber composition is in a second layer on the substrate, and wherein the second layer is directly on the substrate and the first layer is on top of the second layer.
4. The catalytic article of claim 3 , wherein the SCR catalyst composition and the NOx absorber composition are disposed onto the substrate in an axially zoned configuration, wherein the substrate has an axial length with an inlet end and an outlet end, and wherein the second layer is disposed on a first zone extending from the inlet end of the substrate through a range of about 5 to about 95% of the axial length of the substrate.
5. The catalytic article of claim 1 , wherein the NOx absorber composition is substantially free of platinum.
6. The catalytic article of claim 1 , wherein the NOx absorber composition comprises a platinum group metal (PGM) component selected from Ru, Pd, Rh and combinations thereof impregnated onto a support material.
7. The catalytic article of claim 6 , wherein the support material is a molecular sieve or a metal oxide.
8. The catalytic article of claim 7 , wherein the molecular sieve is a zeolite and the metal oxide support comprises ceria.
9. The catalytic article of claim 8 , wherein the metal oxide is doped with at least one lanthanide group metal.
10. The catalytic article of claim 1 , wherein the alkaline earth metal component comprises a barium component.
11. The catalytic article according to claim 1 , wherein the SCR catalyst composition comprises a metal promoted molecular sieve.
12. The catalytic article of claim 11 , wherein the metal is selected from Cu, Co, Ni, La, Mn, Fe, V, Ag, Ce, Nd, Mo, Hf, Y, W, and combinations thereof.
13. The catalytic article of claim 11 , wherein the metal promoted molecular sieve is a zeolite that optionally has a structure type selected from AEI, AFT, AFV, AFX, AVL, CHA, DDR, EAB, EEI, ERI, IFY, IRN, KFI, LEV, LTA, LTN, MER, MWF, NPT, PAU, RHO, RLE, RTH, SAS, SAT, SAY, SFW, TSC, and UFI, and combinations thereof.
14. The catalytic article of claim 1 , wherein the mixed metal oxide component comprises titania and vanadia.
15. The catalytic article of claim 1 , wherein the substrate is a honeycomb substrate selected from the group consisting of a flow-through substrate and a wall flow filter.
16. The catalytic article of claim 1 , wherein the NOx absorber composition does not substantially oxidize ammonia.
17. The catalytic article according to claim 1 , wherein the catalytic article is effective to abate NOx from an engine exhaust gas stream.
18. A method for treating an exhaust gas stream comprising contacting the gas with a catalytic article according to claim 1 such that NOx in the exhaust gas stream is reduced.
19. An emission treatment system for treatment of an exhaust gas stream, the emission treatment system comprising:
an engine producing an exhaust gas stream;
a catalytic article according to claim 1 positioned downstream from the engine in fluid communication with the exhaust gas stream and adapted for the reduction of NOx within the exhaust stream to fora treated exhaust gas stream; and
an injector adapted for the addition of a reductant to the exhaust gas stream positioned upstream of the catalytic article.
20. The emission treatment system of claim 19 , further comprising one or both of a diesel oxidation catalyst located upstream from the catalytic article, and a catalyzed soot filter located downstream from the catalytic article.