Effect of Oxygen Precoverage on the Reactivity of Methanol on Ru(001) Surfaces

Abstract

The thermal decomposition of methanol on oxygen modified Ru(001) surfaces was investigated by reflection−absorption infrared spectroscopy (RAIRS), under UHV conditions. The stability of the different intermediates was interpreted in terms of the oxygen coverage (θO ranging from 0.25 to 0.75 ML), as well as of the methanol dose. For a low methanol exposure at 90 K, dissociative adsorption into methoxide (CH3O−) is favored by increasing oxygen coverage up to 0.6 ML, becoming almost inhibited for θO = 0.75 ML. The reactivity of methoxide is also enhanced by increasing θO from 0.25 to 0.6 ML, as the oxidation temperature drops from 130 to 100 K. Regardless of the oxygen coverage, the oxidation of methoxide yields the intermediate formaldehyde (H2CO), whose stability decreases with increasing θO. Formate (HCOO−) was only identified on surfaces with θO ≥ 0.5 ML, in the temperature range 100 K ≤ T < 130 K, with maximum yield for θO ≈ 0.6 ML. This was the first spectroscopic observation of the intermediate format...