Infrared and Raman study of the adsorption of NH3, pyridine, NO and NO2 on anatase

An anatase precursor of V2O5/TiO2 catalysts contains nitrate and sulphate impurities, the former being destroyed by calcination at 673 K but surface sulphate remaining after calcination at 723 K. Two types of Lewisacidic site were distinguished by ammonia and pyridine adsorption. Slight surface Brønsted acidity was considerably enhanced by deliberate doping with additional surface sulphate. Both nitric oxide and nitrogen dioxide were adsorbed to form bridged and bidentate nitrato species, with monodentate nitrate also formed from the dioxide. Ammonia did not react with the nitrogen oxides on the anatase surface. Co-adsorption was noncompetitive, the two gases being adsorbed at different surface sites.