AN INFRARED STUDY OF ADSORPTION AND MECHANISM OF SURFACE REACTIONS OF 1-PROPANOL ON GAMMA-ALUMINA AND GAMMA-ALUMINA DOPED WITH SODIUM HYDROXIDE AND CHROMIUM OXIDE

Infrared studies of the adsorption of 1-propanol on γ-alumina and the effect of doping the γ-alumina with sodium hydroxide and/or chromium oxide in the temperature range from room temperature to 400° are described. Four different types of surface species were observed: (i) strongly physically hydrogen-bonded propanol to the surface hydroxyl groups; (ii) an aluminum propoxide type structure chemisorbed on Al3+ ions; (iii) a carboxylate structure in which both surface hydroxyl and Al3+ ions are involved; and (iv) a conjugated hydrocarbon species bonded probably to the Al3+ ions. Dehydration mainly occurred on the pure γ-alumina surface, particularly on the high-frequency hydroxyl groups. On the addition of sodium hydroxide, the dehydration reaction was suppressed and the dehydrogenation reaction became dominant. The addition of chromium oxide apparently creates more dehydrogenating sites. The dehydrogenation possibly proceeds via a mechanism involving both carbonium and carbanion ions. The results are correlated by both infrared spectra and mass spectral analysis of the gaseous products.