Catalyst and method for reducing nitrogen oxides in exhaust streams with hydrocarbons or alcohols

• US 20060228283A1
• Filed: 02/24/2006
• Published: 10/12/2006
• Est. Priority Date: 02/28/2005
• Status: Active Grant

• Current Assignee: Catalyst Health Solutions Incorporated (UnitedHealth Group Incorporated)
• Original Assignee: Catalyst Health Solutions Incorporated (UnitedHealth Group Incorporated)
• Inventors: Malyala, Rajashekharam V., Golden, Stephen J.
• Granted Patent: US 8,580,216 B2
• Time in Patent Office: Days
• US Class Current: 423/239.100
• CPC Class Codes: B01D 2251/208 Hydrocarbons
• CPC Class Codes: B01D 2251/21 Organic compounds not provided for in groups B01D2251/206 or B01D2251/208
• CPC Class Codes: B01D 2255/104 Silver
• CPC Class Codes: B01D 2255/502 Beta zeolites
• CPC Class Codes: B01D 2255/504 ZSM 5 zeolites
• CPC Class Codes: B01D 2255/908 O2-storage component incorporated in the catalyst
• CPC Class Codes: B01D 53/8625 Nitrogen oxides
• CPC Class Codes: B01D 53/8628 Processes characterised by a specific catalyst
• 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 21/04 Alumina
• CPC Class Codes: B01J 23/50 Silver
• CPC Class Codes: B01J 23/66 Silver or gold
• CPC Class Codes: B01J 23/83 with rare earths or actinides
• CPC Class Codes: B01J 23/89 combined with noble metals
• CPC Class Codes: B01J 23/894 with rare earths or actinides
• CPC Class Codes: B01J 35/19 Catalysts containing parts with different compositions
• 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 37/0215 Coating
• CPC Class Codes: B01J 37/0234 Impregnation and coating simultaneously
• CPC Class Codes: B01J 37/0242 Coating followed by impregnation
• CPC Class Codes: B01J 37/0246 : Coatings comprising a zeolite

Abstract

A catalyst system and a method for reducing nitrogen oxides in an exhaust gas by reduction with a hydrocarbon or oxygen-containing organic compound reducing agent are provided. The catalyst system contains a silver catalyst and a modifier catalyst, where the modifier catalyst contains a modifier oxide, where the modifier oxide is selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof. The modifier oxide is supported on an inorganic oxide support or supports, where at least one of the inorganic oxide supports is an acidic support. The catalyst system of the silver catalyst and the modifier catalyst provides higher NO_x conversion than either the silver catalyst or the modifier catalyst alone.

Claims

1. A catalyst system for removing nitrogen oxides from an exhaust gas by reduction with a reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds, wherein said exhaust gas contains nitrogen oxides and oxygen in an amount larger than a stoichiometric amount relative to unburned components in said exhaust gas, said catalyst system having an inlet side and an outlet side, said catalyst system comprising:

a first catalyst comprising;

approximately 0.2 to approximately 15 weight percent of at least one silver component selected from the group consisting of silver and silver compounds; and

at least one first inorganic oxide support, wherein the silver component is supported on the first inorganic oxide support; and

a second catalyst comprising;

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one second inorganic oxide support, wherein at least one of the second inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the second inorganic oxide support,

wherein the weight percent of the silver component is on the basis of silver metal relative to the weight of the first inorganic oxide support, and

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the second inorganic oxide support

said first catalyst and said second catalyst being disposed in that order from the inlet side to the outlet side of said catalyst system.

2. The catalyst system of claim 1, wherein the second inorganic oxide support comprises at least one zeolite.

3. The catalyst system of claim 2, wherein at least a portion of the zeolite is at least partially exchanged with at least one element selected from the group consisting of a Group 1A element, a Group 1B element, a Group IIA element, A Group IIB element, a Group IIIB element, a rare earth, and mixtures thereof.

4. The catalyst system of claim 2, wherein at least a portion of the zeolite is in a form selected from the group consisting of the ammonium form and the protonic form.

5. The catalyst system of claim 2, wherein the zeolite is selected from the group consisting of ZSM-5 and beta-zeolite.

6. The catalyst system of claim 2, wherein the zeolite is a mixture of ZSM-5 and beta-zeolite.

7. The catalyst system of claim 1, wherein at least one of the first catalyst and the second catalyst is supported on a substrate.

8. The catalyst system of claim 1, wherein at least one of the first catalyst and the second catalyst is formed into a shape.

9. The catalyst system of claim 8, wherein at least one of the first catalyst and the second catalyst is an extruded catalyst.

10. The catalyst system of claim 1, further comprising an oxidation catalyst, wherein the second catalyst is disposed between the first catalyst and the oxidation catalyst.

11. The catalyst system of claim 1, wherein said second catalyst further comprises an oxygen storage material.

12. The catalyst system of claim 11, wherein said oxygen storage material is a cerium oxide-based material.

13. The catalyst system of claim 1, wherein said reducing agent comprises ethanol.

14. The catalyst system of claim 1, wherein said exhaust gas comprises approximately 1 to approximately 10,000 ppm NO_x.

15. The catalyst system of claim 1, wherein said exhaust gas comprises approximately 1 to approximately 50 ppm NO_x.

16. The catalyst system of claim 1, wherein the modifier oxide is selected from the group consisting of iron oxide, cerium oxide, copper oxide, and manganese oxide.

17. The catalyst system of claim 16, wherein the modifier oxide comprises copper oxide, manganese oxide, and cerium oxide.

19. The method of claim 16, wherein the exhaust gas containing said reducing agent is brought into contact with said catalyst system at a temperature of approximately 300°

C. to approximately 500°

C.

28. A catalyst system of claim 1, wherein, at a given ratio of reducing agent to the nitrogen oxides, an activity of said catalyst system improves over time,.

29. A catalyst system of claim 1, wherein an amount of said reducing agent that is required to reduce said nitrogen oxides decreases over time,

18. A method for removing nitrogen oxides from an exhaust gas by reduction with a reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds, wherein said exhaust gas contains nitrogen oxides and oxygen in an amount larger than a stoichiometric amount relative to unburned components in said exhaust gas, said method comprising:

disposing a catalyst system having an inlet side and an outlet side in a flow path of said exhaust gas;

introducing into said exhaust gas at least one reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds on the inlet side of said catalyst system;

bringing the resulting exhaust gas containing the reducing agent into contact with said catalyst system at a temperature of approximately 150°

C. to approximately 650°

C., thereby reacting said nitrogen oxides with said reducing agent to remove said nitrogen oxides by reduction;

said catalyst system comprising;

a first catalyst comprising;

approximately 0.2 to approximately 15 weight percent of at least one silver component selected from the group consisting of silver and silver compounds; and

at least one first inorganic oxide support, wherein the silver component is supported on the first inorganic oxide support; and

a second catalyst comprising;

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one second inorganic oxide support, wherein at least one of the second inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the second inorganic oxide support,

wherein the weight percent of the silver component is on the basis of silver metal relative to the weight of the first inorganic oxide support, and

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the second inorganic oxide support,

said first catalyst and said second catalyst being disposed in that order from the inlet side to the outlet side of said catalyst system.

21. The exhaust gas treatment apparatus of claim 18, further comprising an oxidation catalyst, wherein the second catalyst is disposed between the first catalyst and the oxidation catalyst.

20. An exhaust gas treatment apparatus comprising:

a catalyst system for removing nitrogen oxides from an exhaust gas by reduction with a reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds, wherein said exhaust gas contains nitrogen oxides and oxygen in an amount larger than a stoichiometric amount relative to unburned components in said exhaust gas, said catalyst system having an inlet side and an outlet side, said catalyst system comprising;

a first catalyst comprising;

approximately 0.2 to approximately 15 weight percent of at least one silver component selected from the group consisting of silver and silver compounds; and

at least one first inorganic oxide support, wherein the silver component is supported on the first inorganic oxide support; and

a second catalyst comprising;

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one second inorganic oxide support, wherein at least one of the second inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the second inorganic oxide support,

wherein the weight percent of said the silver component is on the basis of silver metal relative to the weight of the first inorganic oxide support, and

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the second inorganic oxide support,

said first catalyst and said second catalyst being disposed in that order from the inlet side to the outlet side of said catalyst system;

an exhaust gas source;

a reservoir of reducing agent; and

a means for introducing reducing agent from said reservoir into the exhaust gas generated by said exhaust gas source, wherein said exhaust gas contains nitrogen oxides and wherein said reducing agent is introduced into said exhaust gas on the inlet side of said catalyst system.

22. A modifier catalyst for converting nitrogen-containing intermediates generated by a selective catalytic reduction catalyst from a reducing agent and nitrogen oxides, said modifier catalyst comprising:

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one inorganic oxide support, wherein at least one of the inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the inorganic oxide support,

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the inorganic oxide support.

23. A method for removing nitrogen oxides from an exhaust gas by reduction with a reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds, wherein said exhaust gas contains nitrogen oxides and oxygen in an amount larger than a stoichiometric amount relative to unburned components in said exhaust gas, said method comprising:

disposing a catalyst system having an inlet side and an outlet side in a flow path of said exhaust gas;

introducing into said exhaust gas said at least one reducing agent selected from the group consisting of hydrocarbons and oxygen-containing organic compounds on the inlet side of said catalyst system;

bringing the resulting exhaust gas containing the reducing agent into contact with said catalyst system at a temperature of approximately 150°

C. to approximately 650°

C., thereby reacting said nitrogen oxides with said reducing agent to remove said nitrogen oxides by reduction;

said catalyst system comprising

a first catalyst comprising a selective catalytic reduction catalyst; and

a second catalyst comprising;

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one second inorganic oxide support, wherein at least one of the second inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the second inorganic oxide support,

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the second inorganic oxide support,

said first catalyst and said second catalyst being disposed in that order from the inlet side to the outlet side of said catalyst system.

24. A method for converting nitrogen-containing intermediates into nitrogen comprising:

contacting the nitrogen-containing intermediates with a modifier catalyst comprising;

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one inorganic oxide support, wherein at least one of the inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the inorganic oxide support,

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the inorganic oxide support.

25. A modifier catalyst for converting at least one of carbon monoxide and hydrocarbons generated by a selective catalytic reduction catalyst from a reducing agent and nitrogen oxides or generated by an engine, said catalyst comprising:

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one inorganic oxide support, wherein at least one of the inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the inorganic oxide support,

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the one inorganic oxide support.

26. A method for converting at least one of carbon monoxide and hydrocarbons in a gas stream generated by a selective catalytic reduction catalyst from a reducing agent and nitrogen oxides or generated by an engine, said method comprising:

contacting the gas stream with a modifier catalyst comprising

approximately 1 to approximately 30 weight percent of at least one modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one inorganic oxide support, wherein at least one of the inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the inorganic oxide support,

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the inorganic oxide support.

27. A sulfur-tolerant modifier catalyst for converting at least one of nitrogen-containing intermediates, carbon monoxide and hydrocarbons generated by a selective catalytic reduction catalyst from a reducing agent and nitrogen oxides or generated by an engine, said catalyst comprising:

approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof; and

at least one inorganic oxide support, wherein at least one of the at inorganic oxide supports is an acidic inorganic oxide support,

wherein the modifier oxide is supported on the inorganic oxide support,

wherein the weight percent of the modifier oxide is on the basis of the corresponding metal relative to the weight of the inorganic oxide support.