Infrared Studies of the Mechanism of Methanol Decomposition on Cu/SiO2

The mechanism of methanol decomposition on silica-supported Cu has been investigated by means of infrared spectroscopy and temperature-programmed desorption spectroscopy. Infrared spectra taken during both isothermal and temperature-programmed experiments reveal the following species: methanol, methoxy groups, formaldehyde, methylenebis(oxy) groups, and formate groups. The only products observed during temperature-programmed decomposition are formaldehyde, carbon dioxide, hydrogen, and water. The ratio of hydrogen to carbon dioxide is 0.5 indicating that both products are formed by the decomposition of formate groups on the surface of copper. A mechanism for methanol decomposition is proposed, based on the sequence of species observed during temperature-programmed infrared (TPD-LR) experiments. Simulations of the TPD-IR experiments based on the proposed scheme provide an accurate representation of the observed variations in the concentrations of adsorbed species.