Conversion of hydrocarbons over cobalt oxide catalysts I: Surface and catalytic studies of the cobalt oxide catalysts

Abstract

A cobalt oxide catalyst was prepared by precipitation of cobalt hydroxide from its nitrate solution. It was activated by passing dry air or pure hydrogen through it. Thermogravimetric analyses and X-ray diffraction analyses were carried out and the crystalline size and the surface area for the cobalt oxide catalysts were determined. The cobalt oxide catalyst lost its water of crystallization and water of hydroxylation at 250 °C. The results obtained from the X-ray diffraction measurements were compared with those given in the ASTM cards and the type of crystal was determined at 400, 500 and 750 °C. The crystallite size increased over the temperature range from 400 to 750 °C. From nitrogen adsorption measurements, the specific surface area for the cobalt oxide catalyst was found to be 6.5 m 2 g -1. The catalytic conversion of cyclohexane on the cobalt oxide catalysts was studied using a flow technique. The catalytic activity was measured in the temperaturee range 420 × 490 °C at a space velocity of 6.97 × 10 -2 - 12.11 × 10 -2 min -1 under normal pressure. The gaseous and liquid products of the conversion reaction were analysed using chromatography. The gaseous products were hydrogen and methane. Benzane and cyclohexene were the liquid products, together with unreacted cyclohexane. The kinetics for the gaseous products, cyclohexene and cyclohexene revealed a zero-order reaction. The apparent activation energy was calculated to be 30.8 kcal mol -1 for cyclohexane independent of the space velocity. The formation of different products and the significant gain in the mass of the catalyst after participation in 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 follow the polymolecular mechanism.