The catalytic chemistry of nitric oxide

Abstract

The reduction of NO with H2, CO, and an equimolar mixture of H2CO over supported Pt, Pd, Rh, and Ru catalysts has been studied. The activity sequence of the catalyst tested was Pd > Pt > Rh > Ru when H2 was used as the reducing agent. When CO or a COH2 mixture was used, this activity sequence was reversed. It has been found that CO inhibits NO reduction strongly over Pt and Pd but to a lesser extent over Rh. Over the Ru catalyst the presence of CO accelerates the reaction. The reduction of NO in the presence of Pt and Pd gave NH3 as a major reaction product. Rh and especially Ru catalysts were selective toward N2 formation. The material balance obtained for the Ru catalyst indicates that most of the NO reacts with H2 even if CO is present. Comparative runs indicated that NH3 decomposition is not responsible for the high selectivity toward N2 observed with Ru and Rh catalysts. A reaction mechanism, not involving the ammonia decomposition step, is proposed.