Zeolite catalyst with improved NOx reduction in SCR

• US 7,704,475 B2
• Filed: 12/14/2006
• Issued: 04/27/2010
• Est. Priority Date: 12/14/2005
• Status: Expired due to Fees

• Current Assignee: BASF Corporation (BASF SE)
• Original Assignee: BASF Catalysts LLC (BASF SE)
• Inventors: Moini, Ahmad, Bull, Ivor, Koermer, Gerald Stephen, Roth, Stanley, Jaglowski, William Michael, Patchett, Joseph Allan
• Primary Examiner(s): Vanoy; Timothy C
• Application Number:
  US11/639,182
• Publication Number:
  US 20070134146A1
• Time in Patent Office: 1,230 Days
• Field of Search: 423/239.2, 423/700, 423/713, 502/34, 502/55, 502/60, 502/74, 502/85
• US Class Current: 423/239.2
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/50 Zeolites
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: B01J 2229/16 to increase the Si/Al ratio; Dealumination
• CPC Class Codes: B01J 2229/18 to introduce other elements into or onto the molecular sieve itself
• CPC Class Codes: B01J 2229/186 not in framework positions
• CPC Class Codes: B01J 2229/24 to stabilize the molecular sieve structure
• CPC Class Codes: B01J 2229/36 Steaming
• CPC Class Codes: B01J 2229/37 Acid treatment
• CPC Class Codes: B01J 2229/42 Addition of matrix or binder particles
• CPC Class Codes: B01J 29/061 containing metallic elements added to the zeolite
• CPC Class Codes: B01J 29/072 Iron group metals or copper
• CPC Class Codes: B01J 29/076 containing arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
• CPC Class Codes: B01J 29/084 Y-type faujasite
• CPC Class Codes: B01J 29/088 Y-type faujasite
• CPC Class Codes: B01J 29/146 Y-type faujasite
• CPC Class Codes: B01J 29/166 Y-type faujasite
• CPC Class Codes: B01J 29/40 of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
• CPC Class Codes: B01J 29/46 Iron group metals or copper
• CPC Class Codes: B01J 29/7007 : Zeolite Beta
• CPC Class Codes: B01J 29/7015 : CHA-type, e.g. Chabazite, LZ-218
• CPC Class Codes: B01J 29/7615 : Zeolite Beta
• CPC Class Codes: B01J 29/763 : CHA-type, e.g. Chabazite, LZ-218
• CPC Class Codes: B01J 29/80 : Mixtures of different zeolites
• CPC Class Codes: B01J 29/85 : Silicoaluminophosphates [SAPO compounds]
• CPC Class Codes: B01J 35/023 : Catalysts characterised by dimensions, e.g. grain size
• CPC Class Codes: B01J 35/04 : Foraminous structures, sieves, grids, honeycombs
• CPC Class Codes: B01J 35/1033 : Pore volume
• CPC Class Codes: B01J 35/1052 : Pore diameter
• CPC Class Codes: B01J 35/1095 : polymodal
• CPC Class Codes: B01J 35/40 : characterised by dimensions, e.g. grain size in a colloidal state B01J35/23; crystallite size B01J35/77
• CPC Class Codes: B01J 35/56 : Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• CPC Class Codes: B01J 35/63 : Pore volume
• CPC Class Codes: B01J 35/64 : Pore diameter
• CPC Class Codes: B01J 35/695 : polymodal
• CPC Class Codes: B01J 37/0018 : Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
• CPC Class Codes: B01J 37/0246 : Coatings comprising a zeolite
• CPC Class Codes: Y02C 20/10 : of nitrous oxide (N2O)

Abstract

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 NOx with improved hydrothermal durability. The novel metal-promoted zeolite is formed from a low sodium zeolite and is hydrothermally treated after metal ion-exchange.

Claims

1. A method of preparing a metal-promoted zeolite catalyst for selective catalytic reduction of NOx, said catalyst synthesis comprising the step of:

a. ion-exchanging said metal into a zeolite having the faujasite (FAU) structure and having a sodium content of less than 3.0 wt. % as Na₂O following metal ion-exchange, the metals selected from the group consisting of metal ions of iron, cobalt, and copper,

b. subsequently treating said metal exchanged zeolite with a hydrothermal treatment, and

c. wherein said catalyst has improved NOx reduction activity in selective catalytic reduction compared to metal-exchanged zeolite catalysts not treated by step b.

2. The method of claim 1, wherein said zeolite is treated prior to said ion-exchange by acid dealumination, steam dealumination or extraction of extra-framework aluminum with a complexing agent.

3. The method of claim 1, wherein said zeolite is selected from the group consisting of zeolite Y, faujasites, ultra-stable Y, ZSM-3, ZSM-20, CSZ-1, ECR-30, and LZ-210.

4. The method of claim 3, wherein said zeolite is zeolite Y and said metal is copper.

5. The method of claim 1, wherein said metal ion-exchange is in an aqueous exchange solution having a pH of less than about 5.0.

6. The method of claim 1, wherein said metal ion-exchange is in an aqueous exchange solution having a pH of from about 2.5 to about 3.5.

7. The method of claim 1, wherein more than one ion-exchange step is used and wherein an intermediate calcination step is used between said more than one ion-exchange steps.

8. The method of claim 1, wherein said metal exchanged zeolite is hydrothermally treated at a temperature from about 540°

C. to about 1000°

C., with a steam concentration of from about 5 to about 100%, for about 5 minutes to about 250 hours.

9. The method of claim 1, wherein said metal exchanged zeolite is calcined prior to hydrothermal treatment.

10. The method of claim 1, wherein the zeolite has a pore diameter of at least about 7.4 angstroms.

11. The method of claim 1, wherein said zeolite has a sodium content of less than 0.4 wt. % as Na₂O following metal ion-exchange.

12. A copper containing aluminosilicate zeolite catalyst formed by the method of claim 1.

23. A method of reducing NOx in an exhaust gas or flue gas stream with ammonia and oxygen by selective catalytic reduction said method comprising contacting said exhaust gas or flue gas stream with the metal-promoted zeolite catalyst of claim 12.

13. A hydrothermally stable zeolite catalyst for the selective reduction of nitrogen oxides, said catalyst comprising:

a metal-promoted zeolite having the faujasite (FAU) structure and a sodium content of less than 3.0 wt. % as Na₂O following metal ion-exchange which has been hydrothermally treated after metal ion-exchange to form extra-framework aluminum and wherein a major portion of said extra-framework aluminum is removed from zeolitic pores and said catalyst has improved NOx reduction activity in selective catalytic reduction compared to a metal-exchanged zeolite catalyst that has not been hydrothermally treated after ion exchange, wherein the metal is selected from the group consisting of copper, cobalt and iron.

14. The zeolite catalyst of claim 13, wherein less than 65 wt. % of the total aluminum resides in the zeolitic pores.

15. The metal-promoted zeolite catalyst of claim 13, wherein said zeolite is zeolite Y and said metal is copper.

16. The metal-promoted zeolite catalyst of claim 13, wherein the zeolite contains mesopores having a diameter of 2 to 50 nm and said mesopores have a pore volume of at least 0.07 cm³/g.

17. The hydrothermally stable zeolite catalyst of claim 13, wherein said 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 cation-exchanged zeolite.

18. The metal-promoted zeolite catalyst of claim 13, wherein said metal-promoted zeolite catalyst is coated onto a substrate.

19. The zeolite catalyst of claim 13, wherein a major portion of the extra-framework aluminum has migrated to the external surface of the metal-promoted zeolite.

20. The zeolite catalyst of claim 13, wherein the zeolite has a pore diameter of at least about 7.4 angstroms.

21. The zeolite catalyst of claim 13, wherein said zeolite has a sodium content of less than 0.4 wt. % as Na₂O following metal ion-exchange.

22. The zeolite catalyst of claim 13, wherein the catalyst further comprises a metal selected from the group consisting of vanadium, chromium, manganese, nickel and cerium.

24. A method of reducing NOx in an exhaust gas or flue gas stream with ammonia and oxygen by selective catalytic reduction said method comprising contacting said exhaust gas or flue gas stream with the metal-promoted zeolite catalyst of claim 18.