The Oxidation of Methanol on Cr₂O₃ (101̅2) Single Crystal Surfaces

Abstract

The reaction of methanol with the nearly-stoichiometric and oxygen-terminated surfaces of Cr₂O₃ (101̅2) was studied using thermal desorption spectroscopy and x-ray photoelectron spectroscopy. Dissociative adsorption of methanol occurs on the nearly-stoichiometric surface and is attributed to the presence of cation/anion site-pairs. An array of products including CH₄, CH₂O, CO, CO₂, and H₂ are produced above 550 K on the nearly-stoichiometric surface. Monolayer coverage of methanol yields a 58% conversion to products. Of these products, selectivity to CO is the highest (41%), followed by CH₂O (28%), CH₄ (24%), and CO₂ (7%). At higher temperatures methoxides reversibly undergo dehydrogenation and nucleophilic from lattice oxygen to form dioxymethylene. Hydrogenation of methoxides leads to the formation of CH₄ and CH₃OH above 550 K. Formate is formed as a surface intermediate by reversible dehydrogenation of dioxymethylene. Formaldehyde is produced via C-O bond cleavage of dioxymethylene, and the decomposition of formate yields CO, CO₂, and H₂. The oxygen-terminated surface is unreactive for methanol dissociation due cation site blocking by terminal chromyl oxygen.