Phase Separation within Vanadium Oxide Islands under Reaction Conditions: Methanol Oxidation at Vanadium Oxide Films on Rh(111)

Submonolayer coverages of V-oxide on Rh(111) condense during catalytic methanol oxidation into a pattern of macroscopic stripes or islands. Under reaction conditions, a phase separation occurs within the VOx islands that has been studied in a pressure range of 10(-6)-10(-4) mbar with photoemission electron microscopy (PEEM), low-energy electron microscopy (LEEM), microspot-low-energy electron diffraction (mu LEED), and microspot-X-ray photoelectron spectroscopy (mu XPS). An oxidized outer ring with a (root 7 x root 7)R19.1 degrees structure coexists with an inner (12 x 12) Moire-type boundary layer and a reduced core exhibiting a (root 3 x root 3)R30 degrees Moire type pattern. The dependence of the substructure on the reaction conditions, on V coverage, and on island size was investigated. With mu XPS, the V coverages of the different phases in the VOx islands were determined.