Adsorption of H 2O on the (001) plane of V 2O 5: chemisorption site identification

Abstract

The interaction of water molecules with a polycrystalline V 2O 5 surface has been investigated both by means of a semi-empirical quantum chemistry computational method and by temperature-programmed desorption (TPD). From the TPD desorption spectra, it was found that water desorbed from the V 2O 5 surface at a temperature T p≈350 K with a heating rate of β=10 K min −1. Peak temperature was coverage independent. We explored different chemisorption sites of water molecules on the (001) plane of V 2O 5. Activation energies for each of these sites are calculated and compared with the thermal desorption spectra. From such a comparison we conclude that at room temperature, the water molecule bridges, by hydrogen bonding, two neighboring vanadyl oxygens O(1) with its plane preferentially parallel to the (001) substrate plane. The oxygen atom of the water molecule is above a vanadium atom. TPD spectra are modeled by first order desorption kinetics with a desorption process activation energy of 23.8 kcal mol −1, in agreement with the theoretical calculation of 22–23 kcal mol −1.