Catalytic conversion of alcohols on Al 2O 3-Cr 2O 3 catalysts I: The catalytic decomposition of ethanol

Abstract

The catalytic conversion of ethanol on Cr 2O 3-Al 2O 3 catalysts was studied using a flow technique. The catalytic activity was measured in the temperature range 280–350 °C at a space velocity of 0.37–0.63 min -1 under normal pressure. Three catalyst samples containing 13.62, 16.66 and 39.50 wt.% Cr 2O 3 were prepared by coprecipitation of mixed hydroxides using NH 4OH at 70 °C. The gels obtained were dried at 140 °C and were calcined at 400, 600 and 750 °C. The gaseous and liquid products of the conversion reaction were analysed using chromatography. The gaseous product was mainly ethylene. Water, ether and traces of acetaldehyde and acetone constituted the liquid products, together with unreacted ethanol. The proportion of each liquid depended on the composition of the catalyst and on its calcination temperature. The kinetics of ethylene formation revealed a zero order reaction in all cases and the apparent activation energy was calculated to be 12.5 ± 1.0 kcal mol -1 independent of both the chemical composition and the calcination temperature of the catalyst employed. The catalytic activity and selectivity, however, did depend on catalyst composition and calcination temperature. The formation of acetone and the significant gain in the mass of each catalyst sample after participation in ethanol conversion are explained in terms of the formation of condensation products on the catalyst surface; the conversion may proceed via decomposition of these condensation products or it may follow the polymolecular mechanism proposed by Rudenko.