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 VO x 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 (μLEED), and microspot-X-ray photoelectron spectroscopy (μXPS). An oxidized outer ring with a (√7 × √7)­R19.1° structure coexists with an inner (12 × 12) Moiré-type boundary layer and a reduced core exhibiting a (√3 × √3)­R30° Moiré type pattern. The dependence of the substructure on the reaction conditions, on V coverage, and on island size was investigated. With μXPS, the V coverages of the different phases in the VO x islands were determined.