Conversion of hydrocarbons over an NiAl 2O 3 catalyst I: Surface and catalytic studies of the NiAl 2O 3 catalyst

Abstract

17.99%NiAl 2O 3 was prepared by the coprecipitation of mixed hydroxides from their nitrate solutions. The surface area S BET, the mean pore radius and the crystallite size of the sample were determined. Thermogravimetric and X-ray analyses were also carried out. The analysis of nitrogen adsorption data gave a value of 322 m 2 g −1 for S BET and a value of 11.1 Å for the average pore radius, indicating microporosity. The values of the d spacing obtained from the X-ray analysis were examined and the catalyst type was determined at 400, 600 and 750 °C. The crystallite size increased as the calcination temperature increased from 400 to 750 °C. The catalytic conversion of cyclohexane on an NiAl 2O 3 catalyst was studied using a flow technique. The catalytic activity was measured in the temperature range 400–480 °C at a space velocity of (11.93−48.13) × 10 −4 min −1 under normal pressure. The gaseous and liquid products of the conversion reaction were analysed chromatographically. The gaseous products were methane, ethane and hydrogen, and the liquid products were benzene and cyclohexene together with unreacted cyclohexane. The kinetics of the gaseous products and of cyclohexene and cyclohexane revealed a zero-order reaction, but that of benzene did not. The apparent activation energy was calculated to be 21.08±0.5 kcal independent of space velocity. The formation of different products and the significant gain in the mass of the catalyst after its participation in the cyclohexane 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 have a polymolecular mechanism.