Zeolite-Containing Oxidation Catalyst and Method of Use

Abstract

Oxidation catalyst compositions for treating diesel exhaust include ceria and, optionally, alumina, each having a surface area of at least about 10 m 2 /g, and a zeolite, e.g., Beta zeolite. Optionally, platinum may be included in the catalytic material, preferably in amounts which are sufficient to promote some gas-phase oxidation of carbon monoxide (“CO”) and hydrocarbons (“HC”) but which are limited to preclude excessive oxidation of SO 2 to SO 3 . Alternatively, palladium in any desired amount may be included in the catalytic material. The zeolite is optionally doped, e.g., ion-exchanged, with one or more of hydrogen, a platinum group metal or other catalytic metals. The catalyst compositions may be used in a method to treat diesel engine exhaust by contacting the hot exhaust with the catalyst composition to promote the oxidation of gas-phase CO and HC and of the volatile organic fraction component of particulates in the exhaust.

1 . A diesel engine exhaust treatment system comprising an exhaust stream with a volatile organic fraction, a refractory carrier on which is disposed a coating of a catalytic material comprising a catalytically effective amount of a stabilized ceria having a BET surface area of at least 10 m 2 /g and a catalytically effective amount of a zeolite, wherein the carrier is disposed in the path of the diesel engine exhaust stream.  
   
   
       2 . The diesel engine exhaust treatment system of  claim 1  in which the catalytic material further includes a catalytically effective amount of alumina having a BET surface area of at least about 10 m 2 /g.  
   
   
       3 . The diesel engine exhaust treatment system of  claim 1  wherein the zeolite is selected from the group consisting of beta-zeolite, gamma-zeolite, Pentasil, Mordenite, and mixtures thereof.  
   
   
       4 . The diesel engine exhaust treatment system of  claim 1  wherein the stabilized ceria is stabilized with alumina.  
   
   
       5 . The diesel engine exhaust treatment system of  claim 2  wherein the zeolite comprises from about 10 to 90 percent by weight, the alumina comprises from about 5 to 60 percent by weight, and the ceria comprises from about 5 to 60 percent by weight, of the combined weight of the zeolite, the alumina and the ceria.  
   
   
       6 . The diesel engine exhaust treatment system of  claim 1  wherein the zeolite is doped with a catalytic moiety selected from the group consisting of hydrogen, platinum, rhodium, palladium, ruthenium, osmium, iridium, copper, iron, nickel, chromium, vanadium and combinations thereof.  
   
   
       7 . The diesel engine exhaust treatment system  claim 1  wherein the zeolite is beta-zeolite.  
   
   
       8 . The diesel engine exhaust treatment system  claim 1  wherein the catalytic moiety comprises hydrogen.  
   
   
       9 . The diesel engine exhaust treatment system  claim 1  wherein the zeolite is beta-zeolite and the catalytic moiety comprises hydrogen.  
   
   
       10 . The diesel engine exhaust treatment system of  claim 2  wherein the zeolite is disposed in a discrete layer which is overlain by one or more discrete layers containing the alumina and the ceria.  
   
   
       11 . The diesel engine exhaust treatment system of  claim 1  wherein the refractory carrier has a plurality of parallel exhaust flow passages extending therethrough and defined by passage walls on which the catalytic material is coated, and further comprising dispersed platinum carried on the catalytic material in an amount of from about 0.1 to about 60 g/ft 3 .  
   
   
       12 . The diesel engine exhaust treatment system of  claim 11  wherein the refractory carrier wherein the dispersed platinum is in at least a catalytically effective amount.  
   
   
       13 . The diesel engine exhaust treatment system of  claim 1  wherein the refractory carrier has a plurality of parallel exhaust flow passages extending therethrough and defined by passage walls on which the catalytic material is coated, and further comprising dispersed palladium carried on the catalytic material in a quantity of from about 0.1 to 200 g/ft 3 .  
   
   
       14 . The diesel engine exhaust treatment system of  claim 13  wherein the refractory carrier wherein the dispersed palladium is in at least a catalytically effective amount.  
   
   
       15 . The diesel engine exhaust treatment system of  claim 1  wherein the catalytic material is under oxidizing conditions including a temperature high enough to catalyze oxidation of at least some of the volatile organic fraction.