The Oxidation of Methanol on Cr2O3 (1012) Single Crystal Surfaces

The reaction of methanol with nearly-stoichiometric and oxygen-terminated surfaces of Cr2O3 was studied using thermal desorption spectroscopy and x-ray photoelectron spectroscopy. Dissociative adsorption of methanol occurs on the nearlystoichiometric surface and is attributed to the availability 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 attack from lattice oxygen to create dioxymethylene. Hydrogenation of dioxymethylene back to methoxides leads to the formation of CH4 and CH3OH above 550 K. Formate is formed on the surface 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 at slightly higher temperatures. The oxygen-terminated surface is unreactive for methanol dissociation due to cation site blocking from terminal chromyl oxygen.