Well ordered V2O3(0001) films were grown on Au(111) with a thickness of about 100 Å. These layers are terminated by vanadyl groups under typical UHV conditions. The surface may be reduced by partial of full removal of the oxygen atoms of the vanadyl layer via electron irradiation leading to a surface exposing vanadium atoms. The reactivity of V2O3(0001) with different concentrations of vanadyl groups on the surface has been investigated for methanol, ethanol, and propanol adsorbates using primarily TDS, but also STM, XPS, NEXAFS, and vibrational spectroscopy.
All investigated alcohols do not react with the fully vanadyl terminated surface; only molecular adsorption leading to molecular desorption upon warming up was observed. If part of the oxygen atoms of the vanadyl groups is removed, the alcohols react on the surface. When a methanol layer adsorbed at low temperature is warmed up, two formaldehyde desorption peaks are observed between 500 and 600 K. The relative intensities of these peaks change as a function of the degree of vanadyl oxygen removal, indicating that one of them is related to methanol interacting with vanadyl groups. STM measurements performed for methanol on surfaces with different degrees of removal of vanadyl oxygen show that the remaining vanadyl oxygen atoms are removed from the surface when the methanol layer is warmed up. However, a partial reduction is needed indicating that the reaction starts on sites which expose vanadium atoms. Besides formaldehyde and methanol desorption also water, methane and a small amount of ethylene were observed with details depending in all cases on the degree of vanadyl oxygen removal. The highest amount of water and formaldehyde is observed for weakly reduced surfaces whereas the relative amount of methane is higher for more strongly reduced surfaces. Fewer investigations were performed for ethanol, 1-propanol, and 2-propanol adsorption. Depending on the adsorbed alcohol different reaction products including water, acetone, propanal, ethylene und propene were observed. Similar to the case of methanol, also in the case of these higher alcohols a significant dependence on the concentration of surface vanadyl groups was observed. |