Oxidation State of Vanadium and Role of Titania as the Support for Catalytic Reduction of Nitrogen Monoxide with Ammonia

Abstract

In order to elucidate the catalysis of nitrogen monoxide reduction with ammonia, the changes in oxidation state by the reaction of vanadium supported on silica, titania, and titania coated-silica were studied by use of ESR spectroscopy. The catalysis of the vanadium oxide was found to be inherently correlated with the redox mechanism: V⁵⁺ was reduced by NO-NE3reaction to V⁴⁺ which was reoxidized by oxygen to V⁵⁺. The activity of the supported vanadium oxide was inferred to be mainly determined both by the amount of the effective vanadium ion shuttling between V⁵⁺ and V⁴⁺ and by the rate of the reoxidation of V⁴⁺ to V⁵⁺by oxygen. These two factors were markedly affected by the supports: with titania-supported catalyst the amount of the effective vanadium species was large and the rate of reoxidation of vanadium was high compared with the other two catalysts. The increase in the catalytic activity by treating the silica surface with titania was attributed to the increases both in the amount of the effective vanadium species and in the rate of reoxidation of vanadium.