Water dissociation associated with NO ₂ coadsorption on Mo(110)-(1 × 6)-O: Effect of coverage and electronic properties of oxygen

Water dissociation on an oxygen-covered Mo(110) surface was investigated using temperature-programmed reaction spectroscopy (TPRS) and infrared reflectance absorbance spectroscopy (IRAS). Adsorbed hydroxyl formation is enhanced by increasing the coverage of chemisorbed oxygen prior to exposure to water up to saturation (0.66 ML). Additional oxidation of the surface using NO ₂ suppresses the formation of hydroxyl species (OH). There is no detectable change in the reaction of NO ₂ on Mo(110)-(1 × 6)-O when either the water or hydroxyl is adsorbed on the Mo(110)-(1 × 6)-O surface prior to NO ₂ adsorption. In contrast, NO ₂ induces the displacement of water into the gas phase and the conversion of hydroxyl species to molecular water. Infrared spectra show that the dissociation of NO ₂ populates three types of terminal oxygen sites on Mo(110)-(1 × 6)-O, and the population of the terminal oxygen at step sites increases with respect to the amount of NO ₂ deposited. Overall, these results suggest that the oxidic property of oxygen results in a lack of activity for the water dissociation.