Catalyst system for converting emissions of a lean-burn engine

Abstract

A catalyst system for attaining high conversions of NO, HC, and CO in a fuel-lean emission flow (i.e., containing SO.sub.2, H.sub.2 O, H.sub.2, and considerable excess oxygen), the system comprising: (a) a first stage reducing catalyst for treating the nitric oxide emissions, the catalyst containing highly acidic gamma alumina (i.e., with a pH.sub.pzc of less than 3); (b) means for injecting gaseous or liquid reductants into the emission stream prior to entering said first stage catalyst, said first stage catalyst temperature being selected to be in the range of 550.degree.-650.degree. C.; and (c) an oxidation catalyst effective for treating the effluent from the first stage catalyst. Another aspect of this invention is a method of treating the exhaust gas from a fuel-lean emission flow from a fossil-fueled internal combustion engine having a redox ratio of 0.02-0.09, the method comprising: (a) injecting a gaseous or liquid HC or oxygenated HC reductant into the emission stream at a location where the stream is within the temperature range of 550.degree.-650.degree. C.; (b) immediately exposing the injected stream to a first stage catalyst containing acidic gamma alumina with a pH.sub.pzc of less than 3; and (c) exposing the effluent from the first stage catalyst to an oxidation catalyst that is effective in ensuring that the NO, HC, and CO in the emissions are each converted to at least 80%.

Dependencies are inferred from the claim text.