Treating emissions from engines fueled by compressed natural gas

Abstract

A three-way catalyst system for treating the exhaust stream of a compressed natural gas (CNG) fueled engine operating slightly rich of stoichiometry, the said catalyst system providing high conversions and low light-off temperature for the remnoval of HC, CO, and NO.sub.x. A high surface area gamma alumina support is impregnated with an intimate mixture of 0.2-30% Pd and 0.5-20% La.sub.2 O.sub.3, the Pd being in crystalline form with a particle size in the range of 5.500 angstroms. A method of making such catalyst system comprising sequentially impregnating a high surface area gamma alumina support with lanthana and palladium by incipient wetness techniques, such techniques comprising the procedure of contacting alumina first with a lanthanum nitrate solution of desired concentration to obtain 0.5-20% lanthana, contacting the lanthana impregnated alumina with a palladium nitrate solution of desired concentration to obtain a 0.2-30% palladium content in the catalyst, each of said steps being separated by drying and calcination. A method of treating exhaust gas from a CNG fueled engine with the catalyst system described above, comprising: (a) operating said engine at slightly rich of stoichiometry; (b) exposing such catalyst to the exhaust gases in the range of 400.degree.-750.degree. C. and at a space velocity in the range of 0-100 K hr.sup.-1, said exhaust gas being converted at an efficiency greater than 90% for each of NO, CO, and CH.sub.4.

Dependencies are inferred from the claim text.