Zeolite catalyst containing metals
Provided is catalyst material useful for the selective catalytic reduction of NOx in lean burn exhaust gas, wherein the catalyst material is a hydrothermally stable, low SAR aluminosilicate zeolite loaded with a synergistic combination of one or more transition metals, such as copper, and one or more alkali or alkaline earth metals, such as calcium or potassium.
1. A catalyst composition comprising:
a. an aluminosilicate zeolite material comprising silica and alumina in a CHA framework and having a silica-to-alumina mole ratio (SAR) of about 10 to about 25;
b. about 1 to about 5 weight percent of a base metal (“B M ”), based on the total weight of the zeolite material, wherein said base metal disposed in said zeolite material as free and/or extra-framework exchanged metal;
c. an alkali or alkaline earth metal (collectively “A M ”) disposed in said zeolite material disposed in said zeolite material as free and/or extra-framework exchanged metal,
wherein the B M and A M are present, respectively, in a molar ratio of about 15:1 to about 1:1,
wherein the alumina contains aluminum (Al) that is part of the zeolite framework and the catalyst composition has a (B M +A M ):Al mole ratio of about 0.1 to about 0.4, and
wherein A M is calcium; and
d. about 1 to about 10 weight percent of cerium in said zeolite material, based on the total weight of the zeolite, wherein said cerium is present in a form selected from exchanged cerium ions, monomeric ceria, oligomeric ceria, and combinations thereof, provided that said oligomeric ceria has a particle size of less than 5 μm.
2. The catalyst composition of claim 1 , wherein a molar ratio of B M to Al is less than 0.25:1.
3. The catalyst composition of claim 1 , wherein a molar ratio of B M to A M is about 10:1 to about 3:1.
4. The catalyst composition of claim 1 , wherein said aluminosilicate zeolite material has an SAR of about 15 to about 20 and a B M :Al mole ratio of about 0.1 to about 0.24.
5. The catalyst composition of claim 1 , wherein said base metal is selected from chromium, manganese, iron, cobalt, nickel, and copper, and mixtures thereof.
6. The catalyst composition of claim 1 , wherein said base metal is selected from the group consisting of Cu, Fe, and combinations thereof, and a molar ratio of B M :Al is about 0.17 to about 0.24.
7. The catalyst composition of claim 6 , wherein said base metal is Cu.
8. The catalyst composition of claim 1 , wherein said zeolite is an SSZ-13 isotype.
9. The catalyst composition of claim 2 , wherein said zeolite has a mean crystal size of about 1 μm to about 5 μm.
10. The catalyst composition of claim 1 , wherein said catalyst composition is substantially free of Zr, ZrO, Ti, and TiO.
11. A catalytically active washcoat composition comprising:
a. a catalyst composition according to claim 1 , and
b. one or more stabilizers and/or binders selected from ceria, alumina, silica, (non-zeolite) silica-alumina, naturally occurring clays, TiO 2 , ZrO 2 , and SnO 2 ,
wherein the catalyst composition and the one or more stabilizers and/or binders are present together in a slurry.
12. A catalyst article comprising:
a. a catalyst composition according to claim 1 , and
b. a substrate,
wherein the catalyst composition is disposed on the surface of the substrate, permeates at least a portion of the substrate, or a combination thereof.
13. The catalyst article of claim 12 , wherein said substrate is a flow-through monolith.
14. The catalyst article of claim 12 , wherein said substrate is a wall-flow monolith.
15. A method for reducing NO x in an exhaust gas comprising:
contacting an exhaust gas stream derived from a lean-burn combustion process and containing NO x and a reducing agent with a catalyst composition according to claim 1 ; and
converting at a portion of said NO x to N 2 and H 2 O.