Reaction of methanol on stoichiometric and O-terminated α-Cr2O3 (10(1)over-bar-2):: interconversion of oxygenated C1 surface intermediates

The reaction of methanol on the nearly stoichiometric alpha-Cr2O3 (10 12) surface gives a spectrum of products including CH4, CH2O, CO, CO2 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 inter-conversion 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) over bar2) 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. (C) 2003 Elsevier B.V. All rights reserved.