Infrared and Raman study of the surface acidity of titania-supported vanadia catalysts

Abstract

Infrared and Raman spectra are reported of ammonia and pyridine adsorbed on calcined (in oxygen at 723 K) vanadia catalysts supported on anatase. Infrared results are also given for catalysts which had been reduced in hydrogen at 723 K before adsorption of the bases. Both Lewis- and Brønsted-acidic surface sites exist on oxidised vanadia/anatase with vanadia loadings above and below the theroretical value for monolayer coverage of the anatase. Only Lewis-acidic sites were detected on reduced catalysts. Reduction increased the OH bond strength in surface hydroxyl groups which became unable to donate protons to the bases. Both exposed Ti and V ions acted as Lewis-acidic sites. Ammonia was dissociatively adsorbed at VO sites on vanadia at single-layer coverage on the support.