Catalytic reduction of NOx

Abstract

A system for NO x reduction in combustion gases, especially from diesel engines, incorporates an oxidation catalyst to convert at least a portion of NO to NO 2 , a particulate filter, a source of reductant such as NH 3 and an SCR catalyst. Considerable improvements in NO x conversion are observed.

1 - 14 . (canceled) 
   
   
       15 . A method of reducing NO x  in a gas stream containing NO and particulates, comprising:
 passing the gas stream over an oxidation catalyst thereby converting at least a portion of the NO in the gas stream to NO 2  to form a converted gas stream;   adding a reductant fluid to the converted gas stream to form a gas mixture; and   passing the gas mixture over an SCR catalyst.   
   
   
       16 . The method of claim  4 - 15 , wherein the ratio of NO to NO 2  in the gas mixture is from about 4:1 to 1:3 by volume. 
   
   
       17 . The method of claim  4 - 15 , wherein the gas stream comprises exhaust from sources selected from the group consisting of: heavy duty diesel engines, light duty diesel engines, gasoline direct injection engines, compressed natural gas engines, ships, and stationary sources. 
   
   
       18 . (canceled) 
   
   
       19 . The method of  claim 15 , wherein the gas stream comprises exhaust from a light duty diesel engine. 
   
   
       20 . The method of  claim 15 , wherein the gas stream comprises exhaust from a gasoline direct injection engine. 
   
   
       21 . (canceled) 
   
   
       22 . (canceled) 
   
   
       23 . The method of  claim 15 , wherein the SCR catalyst comprises a transition metal/zeolite catalyst. 
   
   
       24 . The method of  claim 15 , wherein the oxidation catalyst comprises a platinum catalyst. 
   
   
       25 . The method of  claim 24 , wherein the platinum catalyst is deposited on a ceramic through-flow honeycomb support. 
   
   
       26 . The method of  claim 24 , wherein the oxidation catalyst comprises platinum deposited on a metal through-flow honeycomb support. 
   
   
       27 . (canceled) 
   
   
       28 . The method of  claim 15 , wherein the reductant fluid is selected from the group consisting of NH 3 , urea, ammonium carbamate, hydrocarbons, and diesel fuel. 
   
   
       29 . The method of  claim 15 , wherein the reductant fluid comprises NH 3 . 
   
   
       30 . The method of  claim 15 , wherein the reductant fluid comprises urea. 
   
   
       31 . The method of  claim 15 , wherein the reductant fluid comprises ammonium carbamate. 
   
   
       32 . The method of  claim 15 , wherein the reductant fluid is injected into the gas stream. 
   
   
       33 - 94 . (canceled) 
   
   
       95 . A method of improving NO x  conversion in an SCR system, comprising:
 passing the gas stream over an oxidation catalyst thereby converting at least a portion of the NO in the gas stream to NO 2  to form a converted gas stream;   adding a reductant fluid to the converted gas stream to form a gas mixture; and   passing the gas mixture over an SCR catalyst.   
   
   
       96 . The method of  claim 95 , wherein the ratio of NO to NO 2  in the gas mixture is from about 4:1 to 1:3 by volume. 
   
   
       97 . The method of  claim 95 , wherein the gas stream comprises exhaust from sources selected from the group consisting of: heavy duty diesel engines, light duty diesel engines, gasoline direct injection engines, compressed natural gas engines, ships, and stationary sources. 
   
   
       98 . The method of  claim 95 , wherein the SCR catalyst comprises a transition metal/zeolite catalyst. 
   
   
       99 . The method of  claim 95 , wherein the oxidation catalyst comprises a platinum catalyst deposited on a ceramic through-flow honeycomb support. 
   
   
       100 . The method of  claim 99 , wherein the platinum catalyst comprises a Pt/Al 2 O 3  catalyst. 
   
   
       101 . The method of  claim 95 , wherein the reductant fluid comprises urea.  102 - 108 . (canceled) 
   
   
       109 . A process for reducing NO x  present in a lean exhaust gas from an internal combustion engine by selective catalytic reduction on a reduction catalyst using ammonia, comprising oxidizing some of the NO present in the exhaust gas to NO 2  so that the ratio of NO to NO 2  in the exhaust gas is from about 4:1 to 1:3 by volume before contact with the reduction catalyst, wherein oxidation of the NO present in the exhaust gas takes place in the presence of an oxidation catalyst, passing the exhaust gas, together with ammonia, over said reduction catalyst, wherein the reduction catalyst comprises a transition metal/zeolite catalyst. 
   
   
       110 . The process according to  claim 109 , wherein the oxidation catalyst comprises platinum on aluminum oxide. 
   
   
       111 . The process according to  claim 110 , wherein the oxidation catalyst is deposited on a honeycomb carrier. 
   
   
       112 - 136 . (canceled) 
   
   
       137 . A method of reducing NO x  in a gas stream comprising:
 passing the gas stream over an oxidation catalyst thereby incompletely converting NO in the gas stream to NO 2  to form a converted gas stream;   adding a reductant fluid to the converted gas stream to form a gas mixture; and   passing the gas mixture over an SCR catalyst.   
   
   
       138 . The method of  claim 137 , wherein the ratio of NO to NO 2  in the gas mixture is from about 4:1 to 1:3 by volume. 
   
   
       139 . The method of  claim 137 , wherein the gas stream comprises exhaust from sources selected from the group consisting of: heavy duty diesel engines, light duty diesel engines, gasoline direct injection engines, compressed natural gas engines, ships, and stationary sources. 
   
   
       140 . The method of  claim 137 , wherein the SCR catalyst comprises a transition metal/zeolite catalyst. 
   
   
       141 . The method of  claim 137 , wherein the oxidation catalyst comprises a platinum catalyst deposited on a ceramic through-flow honeycomb support. 
   
   
       142 . The method of  claim 141 , wherein the platinum catalyst comprises a Pt/Al 2 O 3  catalyst. 
   
   
       143 . The method of  claim 137 , wherein the reductant fluid comprises urea. 
   
   
       144 - 194 . (canceled)