Surface intermediates in the reaction of methanol, formaldehyde and methyl formate on copper (110)

Abstract

The adsorption and reactions of methanol, methyl formate and formaldehyde on clean and oxygen-covered copper (110) surfaces has been studied with EELS, UPS and temperature programmed desorption (TPD). We report spectroscopic data for (a) the condensed multilayers at 90 K, (b) the surface monolayers and (c) the reaction intermediates formate (HCOO) and methoxy (CH₃O) generated by reaction with surface atomic oxygen. On the clean surface methanol and methyl formate bond via the oxygen and carbonyl lone pair orbitals, whereas formaldehyde always polymerizes to surface paraformaldehyde above 120 K. Atomic oxygen generates methoxy by reaction with methanol and formate by reaction with formaldehyde as reported previously. Methyl formate undergoes nucleophilic attack to form both methoxy and formate in the presence of atomic oxygen, in a similar fashion to the reaction on Ag (110). Whereas the oxidation reactions of these molecules on copper catalysts can be explained with reference to the observed intermediates, no evidence is found for the dimerization of formaldehyde or the dehydrogenation of methanol to form methyl formate: reactions which are quite facile under higher pressure conditions.