Ammonia scr catalyst and method of using the catalyst

Abstract

A catalyst and a method for selectively reducing nitrogen oxides with ammonia are provided. The catalyst includes a first component of copper, chromium, cobalt, nickel, manganese, iron, niobium, or mixtures thereof, a second component of cerium, a lanthanide, a mixture of lanthanides, or mixtures thereof, and a zeolite. The catalyst may also include strontium as an additional second component. The catalyst selectively reduces nitrogen oxides to nitrogen with ammonia at low temperatures. The catalyst has high hydrothermal stability. The catalyst has high activity for conversion of nitrogen oxides in exhaust streams, and are not significantly influenced by the NO/NO 2 ratio. The catalyst and the method may have special application to selective reduction of nitrogen oxides in exhaust gas from diesel vehicles, although the catalyst and the method have broad application to a wide range of gas streams that contain nitrogen oxides. The temperature of exhaust gas from diesel vehicles is low, and the exhaust gas generally has a high NO/NO 2 ratio. Both the low temperature and the high NO/NO 2 ratio are challenging for selective catalytic reduction (SCR) catalysts.

1 - 22 . (canceled) 
     
     
         23 . An apparatus for reducing NOx in an exhaust stream, comprising:
 a substrate comprising a particulate filter; and   a catalyst for selective catalytic reduction of nitrogen oxides with ammonia, the catalyst comprising:
 a first component comprising at least one of the group consisting of copper, chromium, cobalt, nickel, manganese, iron, niobium, and mixtures thereof; 
 a second component comprising at least one of the group consisting of cerium, a lanthanide, a mixture of lanthanides, and mixtures thereof, and 
 at least one zeolite, 
   wherein the catalyst is placed on the substrate.   
     
     
         24 . The catalyst composition of  claim 23 , further comprising an oxygen storage material. 
     
     
         25 . The catalyst composition of  claim 24 , further comprising at least one inorganic oxide selected from the group consisting of alumina, silica, titania, and silica-alumina solutions, composites, and mixtures thereof. 
     
     
         26 . The catalyst composition of  claim 25 , wherein at least one of the zeolite, the oxygen storage material, and the inorganic oxide is placed on the substrate in a form of a washcoat. 
     
     
         27 . The catalyst composition of  claim 23 , wherein the catalyst comprises approximately 1 to approximately 20 weight percent of the first component, approximately 2 to approximately 35 weight percent of the second component, and approximately 10 to approximately 90 weight % of the at least one zeolite, wherein the weight percentages of the first component and the second component are on the basis of the metals. 
     
     
         28 . The catalyst composition of  claim 27 , wherein the catalyst further comprises approximately 2 to approximately 35 weight percent of strontium, wherein the weight percent of the strontium is on the basis of strontium metal. 
     
     
         29 . The catalyst composition of  claim 23 , wherein the zeolite is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-18, ZSM-23, MCM-zeolites, mordenite, faujasite, ferrierite, zeolite beta, and mixtures thereof. 
     
     
         30 . The catalyst composition of  claim 24 , wherein the oxygen storage material is selected from the group consisting of Ce 1-a Zr a O 2  and Ce 1-c-d Zr c Lan d O 2 , wherein Lan is selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Ho, Yb and mixtures thereof. 
     
     
         31 . The catalyst composition of  claim 23 , wherein the first component is manganese, the second component is cerium, and the zeolite is ZSM-5. 
     
     
         32 . The catalyst composition of  claim 23 , wherein the particulate filter comprises a ceramic support. 
     
     
         33 . The catalyst composition of  claim 32 , wherein the ceramic support comprises a material selected from the group consisting of cordierite and silicon carbide. 
     
     
         34 . The catalyst composition of  claim 33 , wherein the particulate filter comprises a wall flow filter. 
     
     
         35 . The apparatus of  claim 34 , wherein the particulate filter comprises a diesel particulate filter. 
     
     
         36 . A method for selective reduction of nitrogen oxides in a gas stream with ammonia, wherein the gas stream comprises nitrogen oxides, the method comprising:
 contacting the gas stream with ammonia in the presence of a catalyst composition, the catalyst composition comprising:   a substrate comprising a particulate filter; and   a catalyst, comprising:
 a first component comprising at least one of the group consisting of copper, chromium, cobalt, nickel, manganese, iron, niobium, and mixtures thereof; 
 a second component comprising at least one of the group consisting of cerium, a lanthanide, a mixture of lanthanides, and mixtures thereof; and 
 at least one zeolite, 
   
       wherein the catalyst is placed on the substrate. 
     
     
         37 . The method of  claim 36 , wherein the gas stream is contacted with ammonia at a temperature of approximately 140 to approximately 700 degrees Centigrade and has an ammonia/NO x  mole ratio of approximately 0.6 to approximately 2.0. 
     
     
         38 . The method of  claim 36 , wherein the catalyst further comprises strontium. 
     
     
         39 . The method of  claim 36 , wherein the catalyst further comprises an oxygen storage material. 
     
     
         40 . The method of  claim 36 , wherein the catalyst comprises approximately 1 to approximately 20 weight percent of the first component, approximately 2 to approximately 35 weight percent of the second component, and approximately 10 to approximately 90 weight % of the at least one zeolite, wherein the weight percentages of the first component and the second component are on the basis of the metals. 
     
     
         41 . The method of  claim 40 , wherein the catalyst further comprises approximately 2 to approximately 35 weight percent of strontium, wherein the weight percent of the strontium is on the basis of strontium metal. 
     
     
         42 . The method of  claim 36 , wherein the zeolite is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-18, ZSM-23, MCM-zeolites, mordenite, faujasite, ferrierite, zeolite beta, and mixtures thereof. 
     
     
         43 . The method of  claim 39 , wherein the oxygen storage material is selected from the group consisting of Ce 1-a Zr a O 2  and Ce 1-c-d Zr c Lan d O 2 , wherein Lan is selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Ho, Yb and mixtures thereof. 
     
     
         44 . The method of  claim 36 , wherein the first component is manganese, the second component is cerium, and the zeolite is ZSM-5. 
     
     
         45 . The method of  claim 36 , further comprising contacting the gas stream and ammonia with at least one inorganic oxide selected from the group consisting of alumina, silica, titania, and silica-alumina solutions, composites, and mixtures thereof. 
     
     
         46 . The method of  claim 36 , wherein the particulate filter comprises a ceramic support. 
     
     
         47 . The method of  claim 46 , wherein the ceramic support comprises a material selected from the group consisting of cordierite and silicon carbide. 
     
     
         48 . The method of  claim 47 , wherein the particulate filter comprises a wall flow filter. 
     
     
         49 . The method of  claim 48 , wherein the particulate filter comprises a diesel particulate filter.