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Adsorption and Reaction of Methanol on Clean and Oxygen Precovered Cu(111)

Abstract The adsorption of methanol on the clean and oxygen precovered Cu(111) surface was studied by means of high resolution X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and temperature programmed desorption (TPD). On clean Cu(111) methanol is adsorbed molecularly at 100 K. Only small amounts of methoxy are formed by heating to 160–180 K, whereas the main part of methanol desorbs molecularly. The formation of methoxy drastically increases on the oxygen precovered surface. In the UP spectra the peaks of molecular methanol disappear and the peaks of methoxy develop. TPD measurements show that methoxy desorbs dissociatively as formaldehyde and hydrogen with the rate maxima at around 430 K. The efficiency of the oxidation of methanol to formaldehyde depends on the amount of predosed oxygen, with a maximum methoxy coverage obtained for an oxygen precoverage of 0.18 ML. From the quantitative analysis we propose an additional reaction pathway involving not only the formation, but also the decomposition of an hydroxyl intermediate, parallel to the previously reported pathway, which leads to the desorption of water.