Temperature-programmed desorption of methanol, ethanol, propan-1-ol and propan-2-ol on silica–magnesia mixed oxides

Abstract

The adsorption of methanol, ethanol, propan-1-ol and propan-2-ol on silica, silica–magnesia mixed oxides and magnesia has been studied by means of temperature-programmed desorption (t.p.d.). Besides the desorption of the alcohols themselves, CH₂O, CO and H₂ have been found to desorb upon adsorption of methanol, the corresonding olefins upon adsorption of the other alcohols and also propan-2-one upon adsorption of propan-2-ol. The desorption behaviour and alcohol conversion are discussed in terms of the EPA (electron-pair acceptor)–EPD (electron-pair donor) concept. The t.p.d. peaks of the alcohols have been assigned to two adsorption structures with different interaction strengths. The desorption maxima of the products have been found at higher temperatures than those of the alcohols, the difference being at least 50 °C. CO, H₂ or the olefins were found with all oxides, whereas formaldehyde was only observed with oxides of lower base strength and propan-2-one with oxides of higher base strength.