Treating exchaust from a compressed natural gas-fueled engine

Abstract

A catalyst system that converts the exhaust gas of a compressed natural gas (CNG) fueled automotive engine when operated at stoichiometry or slightly lean thereof, at highly enhanced rates, and having: (a) a first stage catalyst comprising a transition metal-containing zeolite (Cu-ZSM5), and (b) a second stage catalyst for treating the effluent of the first stage and comprising palladium supported on high surface area gamma alumina. The second stage catalyst has the alumina support impregnated with an intimate mixture, by weight, of 0.5-20% La.sub.2 O.sub.3 and 0.2-30% palladium. A method of treating exhaust gases from a CNG-fueled engine, comprising: (a) operating the engine at stoichiometry or slightly lean (0.85-1.0 R) thereof; (b) exposing such exhaust gases to a first stage catalyst consisting of a copper-ZSM5 zeolite having at least 3% by weight ion exchange copper; and (c) exposing the effluent from the first stage to a second stage comprising a gamma alumina support catalyst impregnated with palladium and other catalyst enhancing oxides.