Extruded Zeolite Catalysts for Lean Exhaust Application

In lean burn engines, the conventional automotive catalyst is ineffective in reducing harmful nitric oxide (NO_x) wastes. This study has investigated the use of different materials with metal additives as supports for effective NO_x- controlling lean burn catalysts. A series of zeolite (ZSM-5) honeycomb samples were prepared via extrusion with low concentrations of transition metals. Samples were also impregnated with Pt to determine the effect on the catalytic activity. NO_x and hydrocarbon conversion under simple lean conditions were measured in a temperature-controlled fixed bed reactor. Ethylene and Propylene, both highly selective NO_x reductants, were used separately as the hydrocarbon species. Results have revealed that single and double component zeolites containing Ni, Mn, Cu, and Ag are highly effective in reducing NO_x. When these same samples were impregnated with Pt, they achieved conversion rates up to 100% at temperatures less than 300°C at a space velocity of 7000 h^-1. At higher space velocities, up to 80% NO conversion is observed for some catalysts. The performance of the Ni-Co catalyst remains encouraging and is not impaired by moderate aging conditions and by the presence of water.