INTERACTION OF METHANE WITH SURFACE OF ALUMINA STUDIED BY FT-IR SPECTROSCOPY

Methane adsorption on alumina was investigated by FT-IR spectroscopy at 173 K. Adsorbed methane gives four distinct IR bands at 3008, 3000, 2900 and 1305 cm(-1) which are attributed to nu(1) (2900 cm(-1)), nu(3) (3008, 3000 cm(-1)), and nu(4) (1305 cm(-1)) modes of methane respectively. The appearance of the nu(1) mode indicates that the T-d symmetry of methane is distorted by the adsorption. The intensities of these bands increase significantly with outgassing temperatures of alumina, reach their maxima at an outgassing temperature near 773 K, and then decrease with further higher outgassing temperatures. Two hydroxyls with IR bands at 3750 and 3665 cm(-1) are perturbed evidently by the adsorbed CH4 thereby resulting in two redshifted bands at 3707 and 3640 cm(-1). Coadsorbed CO slightly affects the adsorbed CH4 indicating the very weak interaction between CH4 and surface cations of alumina. It is proposed that the adsorbed CH4 on alumina is formed mainly via the interaction of CH4 with both surface hydroxyl and c.u.s. oxygen anion.