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TiO2(110)
Mo+Ti mixed oxide
Methanol adsorption
Ethanol adsorptio
Abstract:
We present a STM/XPS/TPD/LEED study of the structural and electronic properties of Mo+Ti mixed oxide layers on TiO2(110), and of their interaction with water, methanol and ethanol. Several different preparation procedures were tested and layers with different degrees of Mo/Ti mixing were prepared. Ordered mixed oxide surface phases with distinct LEED patterns could not be found; for all investigated Mo concentrations a TiO2(110) like pattern was observed. Mo tends to agglomerate on the surface where it is found predominantly as Mo6+ at low coverages and as Mo4+ at high coverages. Mo4+ was also identified in the bulk of the mixed oxide layer. The Mo3d binding energies categorize the Mo4+ species as being dimeric. A third Mo3d doublet is attributed to a Mo species (Mon+) with an oxidation state between those reported for Mo in MoO2 and metallic Mo. Two types of Mo-induced features could be identified in the STM images for low Mo concentrations (in the range of 1 %). At higher Mo concentrations (~50 %) the surface is characterized by stripes with limited lengths in [001] direction. The concentration of bridging oxygen vacancies, which are common defects on TiO2(110), is reduced significantly even at low Mo concentrations. Methanol and ethanol TPD spectra reflect this effect by a decrease of the intensity of the features related to these surface defects. At elevated MoOx coverages, the yield of reaction products in methanol and ethanol TPD spectra are somewhat smaller than those found for clean TiO2(110) and the reactions occur at lower temperature.
