Infrared study of the reaction between nitrogen oxides and ammonia on titania-supported vanadia catalysts

Abstract

Infrared spectroscopy has been used to study sequential adsorption of ammonia and nitric oxide and of ammonia and nitrogen dioxide on three anatase-supported vanadia catalysts with different vanadia loadings. Facile reaction occurred between ammonium ions at Brønsted-acidic surface sites on vanadia and nitrato species formed by the adsorption of nitrogen dioxide or nitric oxide. Nitric oxide was less reactive because of depletion of surface oxygen during reaction. Pre-reduction of catalyst in hydrogen not only removed surface oxygen but also destroyed catalytically active Brønsted-acidic sites. A reaction mechanism involving an intermediate V—O—NN species is tentatively proposed.