The Oxidation of Methanol on Cr2O3 (1012) Single Crystal Surfaces
Mensch, Michael W
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The reaction of methanol with the nearly-stoichiometric and oxygen-terminated surfaces of Cr2O3 (1012) 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.
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