Chemisorption of NH₃ on Monomeric Vanadium Oxide Supported on Anatase TiO₂: A Combined DRIFT and DFT Study

V/TiO₂ catalysts are used in various reactions, including oxidative dehydrogenation, partial oxidation of ethanol, and selective catalytic reduction of NO_x with NH₃. In this work, we investigated the effect of supported monomeric vanadium oxide (VO₃) on the acidity of anatase TiO₂(101) surface by using density functional theory calculations combined with in situ diffuse reflectance infrared Fourier transform (DRIFT) experiments. The hydrogenation of TiO₂ to form hydroxyl groups on the surface was energetically more favorable in the presence of the supported monomeric vanadium oxide. Charge transfer between TiO₂ support and VO₃ was considered as an origin of -OH stabilization, which made Brønsted acid sites more abundant on the V/TiO₂ surface than on TiO₂. Moreover, it was observed that the cationic vanadium center in VO₃ can act as much weaker Lewis acid sites than the titanium center in TiO₂. Such weakened acidity of Lewis acid sites in the presence of monomeric vanadium oxide was consistently observed in in situ DRIFT results, which could explain the higher reactivity of NH₃ adsorbed on Lewis acid sites of V/TiO₂ than those of TiO₂ in the NH₃-selective catalytic reduction reaction.