Reaction of methanol on stoichiometric and O-terminated α-Cr 2O 3 ( [formula omitted]): interconversion of oxygenated C 1 surface intermediates

Abstract

The reaction of methanol on the nearly stoichiometric α-Cr 2O 3 ( 1 0 1 ̄ 2 ) surface gives a spectrum of products including CH 4, CH 2O, CO, CO 2 and H 2. These products are all generated in a 200 K temperature range (600–800 K) in thermal desorption through a reaction pathway involving methoxide, dioxymethylene and formate surface intermediates. The interconversion between oxygenated C 1 surface intermediates involves the reversible reaction of methoxide to dioxymethylene via dehydrogenation and nucleophilic attack of surface lattice oxygen. Formate intermediates are subsequently formed by the dehydrogenation of dioxymethylene. Isotopic labeling studies indicate that the precursor to the formaldehyde reaction product is a dioxymethylene intermediate rather than methoxide. The oxygen-terminated surface is completely unreactive, indicating a structure (or composition) sensitive reaction of methanol on the ( 1 0 1 ̄ 2 ) surface. Terminal chromyl oxygen acts as a cation site blocker and eliminates the surface cation–anion site pairs necessary for the dissociation and reaction of methanol.