Reactive Phase Separation during Methanol Oxidation on a V-Oxide-Promoted Rh(110) Surface
2018
von Boehn, Bernhard | Menteş, Tevfik O. | Locatelli, Andrea Maria | Sala, Alessandro | Imbihl, Ronald
The distribution of ultrathin layers of vanadium oxide on Rh(110) (θV ≤ 1 MLE, one monolayer equivalent corresponds to the number of Rh atoms in the topmost Rh(110) surface layer) after exposure to catalytic methanol oxidation in the 10–⁴ mbar range has been investigated with x-ray photoelectron spectroscopy and spectroscopic low-energy electron microscopy (SPELEEM). The reaction is shown to cause a macroscopic phase separation of the VOₓ film into VOₓ-rich and into V-poor phases. For θV = 0.8 MLE compact VOₓ islands develop whose substructure exhibits several ordered phases. At θV = 0.4 MLE the VOₓ-rich phase consists of many small VOₓ islands (0.1–1 μm). Laterally resolved x-ray photoelectron spectroscopy of V 2p₃/₂ shows an oxidic component at 515.5 eV binding energy (BE) and a component at 513.0 eV BE attributed to metallic or strongly reduced V. On the V-poor phase only the reduced/metallic component is present. The results are compared with the distribution of ultrathin layers of vanadium oxide on Rh(111) after catalytic methanol oxidation. The presence of the metallic V on Rh(110) is at variance with the behavior of Rh(111), where V is found to be present only in high oxidation states during methanol oxidation.
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