Methanol Adsorption and Oxidation on Reduced and Oxidized TbOx(111) Surfaces
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We used temperature programmed reaction spectroscopy (TPRS) and synchrotron-radiation based photoelectron spectroscopy (PES) to investigate the adsorption and oxidation of methanol (CH3OH) on Tb2O3(111) and TbO2(111) thin films grown on Pt(111). We find that methanol mainly desorbs from the Tb2O3 surface through both molecular and recombinative processes, and that a relatively small amount of adsorbed methanol (< 20%) dehydrogenates to CH2O and H2O with these species desorbing between about 160 and 300 K. Oxidation of the terbia film enhances the surface reactivity as ~50% of the adsorbed methanol on TbO2 oxidizes to mainly CH2O and water as well as CO2 that desorbs near 600 K during TPRS. Quantification of the product yields suggests that all of the excess surface O-atoms, resulting from oxidation of Tb2O3 to TbO2, are removed during TPRS by reaction with adsorbed CH3OH. We did not detect CO or H2 production under any conditions. PES measurements show that several adsorbed intermediates form on the TbOx surfaces at temperatures as low as 140 K, including mainly methoxy (CH3O) as well as smaller quantities of a more oxidized species, thought to be either CH2O2 or CHO2. XPS spectra collected as a function of the surface temperature provide evidence that the adsorbed CH3O groups serve as the main intermediate for both CH2O and CH3OH formation at temperatures below 400 K, while the more oxidized species is a spectator to CH2O formation but undergoes complete oxidation on TbO2 at temperatures above 450 K. The high reactivity of the TbO2 surface correlates with the presence of labile oxygen atoms that are generated during oxidation of the Tb2O3 film.