Zeolite catalyst with improved NOx reduction in SCR
The present invention is directed to a novel metal-promoted zeolite catalyst, a method of producing the catalyst and a method of using the catalyst for the selective catalytic reduction of NO x with improved hydrothermal durability. The novel metal-promoted zeolite is formed from a low sodium zeolite and is hydrothermally treated after metal ion-exchange.
1. A method of reducing NOx in an exhaust gas or flue gas stream with ammonia and oxygen by selective catalytic reduction, the method comprising contacting said exhaust gas or flue gas stream with a hydrothermally stable zeolite catalyst comprising a metal-promoted, low sodium zeolite, wherein said metal-promoted, low sodium zeolite has been treated to form extra-framework aluminum and remove a major portion of said extra-framework aluminum from zeolite pores.
2. The method of claim 1 , wherein said metal-promoted, low sodium zeolite has a sodium content of less than 3 weight percent as Na 2 O following metal ion-exchange and is hydrothermally treated after metal ion-exchange to form the extra-framework aluminum and remove the major portion of the extra-framework aluminum from the zeolite pores.
3. The method of claim 1 , wherein the method exhibits improved NOx reduction activity in selective catalytic reduction as compared to a method using a metal-promoted, low sodium zeolite catalyst not treated to form extra-framework aluminum and remove a major portion of said extra-framework aluminum from zeolite pores.
4. The method of claim 3 , wherein the improved NOx reduction activity in selective catalytic reduction is at a temperature at or below 350° C.
5. The method of claim 1 , further comprising converting greater than 50% of the NOx gases in the exhaust gas or flue gas stream at temperatures at or below about 250° C.
6. The method of claim 1 , further comprising converting greater than 80% of the NOx gases in the exhaust gas or flue gas stream at temperatures at or below about 300° C.
7. The method of claim 1 , wherein less than 65 wt. % of the total aluminum resides in the zeolite pores.
8. The method of claim 1 , wherein said metal-promoted, low sodium zeolite is zeolite Y and said metal is copper.
9. The method of claim 1 , wherein said metal-promoted, low sodium zeolite contains mesopores having a diameter in the range of 2 to 50 nm and said mesopores have a pore volume of at least 0.07 cm 3 /g.
10. The method of claim 1 , wherein said metal-promoted, low sodium zeolite contains a metal loading at the external surface of the zeolite from about 1 wt. % to about 10.0 wt. %, based on the weight of the metal-promoted, low sodium zeolite.
11. The method of claim 1 , wherein said hydrothermally stable zeolite catalyst is coated onto a substrate.
12. The method of claim 1 , wherein a major portion of the extra-framework aluminum has migrated to the external surface of said metal-promoted, low sodium zeolite.
13. The method of claim 1 , wherein said metal-promoted, low sodium zeolite is treated by acid dealumination, steam dealumination or extraction of extra-framework aluminum with a complexing agent to remove the major portion of said extra-framework aluminum from the zeolite pores.
14. The method of claim 1 , wherein said metal-promoted, low sodium zeolite is selected from the group consisting of zeolite Y, faujasites, ultra-stable Y, ZSM-3, ZSM-20, CSZ-1, ECR-30, LZ-210, zeolite L, ferrierite, MCM-22 and offretite.
15. The method of claim 1 , wherein said metal-promoted, low sodium zeolite is promoted with a metal selected from the group consisting of metal ions of vanadium, chromium, manganese, iron, cobalt, nickel, copper and cerium.
16. The method of claim 1 , wherein said metal-promoted, low sodium zeolite has a sodium content of less than 3.0 wt. % as Na 2 O following metal ion-exchange.
17. The method of claim 16 , wherein the sodium content is less than 2.4 wt. % as Na 2 O following metal ion-exchange.
18. The method of claim 17 , wherein the sodium content is less than 1.0 wt. % as Na 2 O following metal ion-exchange.
19. The method of claim 18 , wherein the sodium content is less than 0.4 wt. % as Na 2 O following metal ion-exchange.