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 NOx 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 Bronsted 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.