Water (Non-)Interaction with MoO3.

Ashley R Head,Bryan Eichhorn,Hendrik Bluhm,Yi Yu,Chiara Gattinoni,Lena Trotochaud,Osman Karslıoğlu,Sven Pletincx

doi:10.1021/acs.jpcc.9b03822

Abstract

Molybdenum(VI) oxide (MoO3) 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 MoO3 and thus the course of heterogeneous reactions. We use ambient pressure X-ray photoelectron spectroscopy to study the interaction of water with a stoichiometric MoO3 surface and a MoO3 surface that features oxygen defects and hydroxyl groups. The experimental results are supported by density functional theory calculations. We show that on a stoichiometric MoO3(010) surface, where Mo sites are unavailable, water adsorption is strongly disfavored. However, the introduction of surface species, which can interact with the lone pairs on the water O atom, e.g., Mo5+ 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.

Highlights

Water interaction with metal oxide surfaces plays an important role in many processes ranging from electrochemistry and corrosion to environmental chemistry
In a step toward understanding how relative humidity (RH) affects the surface chemistry, we have studied MoO3 from ultrahigh vacuum (UHV) to 6% RH using ambient pressure X-ray photoelectron spectroscopy (APXPS)
As the APXPS data show, despite relative humidity conditions that exceed this threshold by nearly 3 orders of magnitude (6% RH), no significant amount of water adsorption or hydroxylation was seen in the APXPS data of the pristine MoO3 sample

Summary

Introduction

Water interaction with metal oxide surfaces plays an important role in many processes ranging from electrochemistry and corrosion to environmental chemistry These interactions include adsorption and dissociation and, in turn, influence other heterogeneous reactions due to the presence of water molecules and hydroxyls.[1] This last point is relevant to air filtration materials used in the removal of toxic organic molecules, such as industrial chemicals and nerve agents. These filtration materials are often composed of porous carbon impregnated with metal oxides.[2] How these filtration materials, including the metal oxides, interact with ambient water vapor during storage and use is still largely unknown. Of great concern is how humidity impacts reactions with other atmospheric gases, such as NOx and SOx, and the effectiveness of air filtration materials under standard application scenarios

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Conclusion