Bimetallic catalyst for nox reduction in engine exhaust

Abstract

A catalyst made by the introduction of copper ions and cobalt ions into a Y-type zeolite to produce a CuCoY zeolite improves the reduction of NOx in exhaust from a lean burn engine, such as a diesel engine. A dual bed selective reduction reactor in the exhaust stream comprising a first bed of BaY or of Ag/alumina and a second bed of CuCoY is particularly effective in reduction of NOx. In one embodiment, the exhaust stream is suitably treated with an oxidant, such as ozone, and a reductant, such as a diesel hydrocarbon or oxygenated diesel hydrocarbon, before the exhaust passes in contact with the dual bed catalyst.

1 - 10 . (canceled) 
     
     
         11 . A method of making a catalyst for reducing nitrogen oxides in an exhaust stream from an engine operating in a lean burn mode, the exhaust stream comprising NO, NO 2 , oxygen, water, and nitrogen; the method comprising:
 exchanging copper ions in water for other base metal ions in a Y type zeolite and   exchanging cobalt ions in water for other base metal ions in a Y type zeolite.   
     
     
         12 . A method of making a catalyst for reducing nitrogen oxides as recited in  claim 11  in which copper ions in water are first exchanged with a first portion of other base metal ions and cobalt ions are subsequently exchanged with a second portion of base metal ions. 
     
     
         13 . A method of making a catalyst of reducing nitrogen oxides as recited in  claim 12  in which copper ions in water are twice exchanged for base metal ions before cobalt ions are exchanged for the other base metal ions in the Y type zeolite. 
     
     
         14 . A method of making a catalyst of reducing nitrogen oxides as recited in  claim 12  in which cobalt ions are exchanged a single time for other base metal ions in the Y type zeolite. 
     
     
         15 . A method of making a catalyst for reducing nitrogen oxides as recited in  claim 11  in which the other base metal ions are sodium ions. 
     
     
         16 . A method of making a catalyst as recited in  claim 11  in which the ion exchange steps are conducted to obtain catalyst particles comprising, by weight, about three to about six percent copper and about one and one-half percent to about three percent cobalt.