NOx Emission Control in Oxygen-Rich Exhaust Through Selective Catalytic Reduction by Hydrocarbon

Abstract
Selective catalytic reduction of nitrogen monoxide by hydrocarbon in the presence of oxygen and sulphur dioxide has very recently been found on copper ion-exchanged ZSM-5 zeolite (Cu-ZSM-5). The reaction proceeds even in the oxidizing atmosphere at temperatures as low as 573 K. Addition of oxygen to the reactant stream is necessary to achieve the selective reduction of nitrogen monoxide. The increment of concentration of hydrocarbon increased the conversion into nitrogen and expanded the active temperature region. After summarizing the new findings on Cu-ZSM-5, the present review introduces catalytic activities of various metal-ion exchanged zeolites and metal-loaded aluminas. Based on the temperature dependence of each catalyst and the change of conversion of nitrogen monoxide into nitrogen with space velocity, Cu-ZSM-5 is suggested as one of the strong candidates for catalysts applicable to lean-burn gasoline and diesel engines, though several problems such as durability to water and overheating remain to be solved.