Water (Non-)Interaction with MoO₃

Abstract

Molybdenum(VI) oxide (MoO<sub>3</sub>) is used in a number of technical processes such as gas filtration and heterogeneous catalysis. In these applications, the adsorption and dissociation of water on the surface can influence the chemistry of MoO<sub>3</sub> and thus the course of heterogeneous reactions. We use ambient pressure X-ray photoelectron spectroscopy to study the interaction of water with a stoichiometric MoO<sub>3</sub> surface and a MoO<sub>3</sub> surface that features oxygen defects and hydroxyl groups. The experimental results are supported by density functional theory calculations. We show that on a stoichiometric MoO<sub>3</sub>(010) surface, where Mo sites are unavailable, water adsorption is strongly disfavored. Furthermore, the introduction of surface species, which can interact with the lone pairs on the water O atom, e.g., Mo<sup>5+</sup> atoms or surface OH groups, promotes water adsorption. Dissociation of water is favored at unsaturated Mo sites, i.e., at oxygen vacancies, while water adsorbs molecularly at hydroxyl sites.