PERFORMANCE OF PLATINUM-GROUP METAL-CATALYSTS FOR THE SELECTIVE REDUCTION OF NITROGEN-OXIDES BY HYDROCARBONS

The performances of platinum-group metals, platinum, iridium, palladium, rhodium and ruthenium supported on gamma-alumina, as catalysts for the selective reduction of nitrogen oxides by hydrocarbons were investigated. Platinum and rhodium had high nitric oxide conversion activities both in model mixtures and in real diesel exhaust gases. especially at relatively low temperatures between 200 and 350-degrees-C. It was confirmed that the platinum-rhodium and platinum catalysts have higher activity and durability than a catalyst composed of copper supported on ZSM-5 under real diesel exhaust conditions. The platinum-containing catalysts, however, produced more nitrous oxide than nitrogen. It is expected that platinum-group metal catalysts will be able to be used for practical purposes if once their selectivity toward nitrogen is improved.