Influence of the nature of the activating molecules on the catalytic activity of cobalt—molybdenum/alumina catalysts

The effectiveness of the activation of a commercial CoMo/Al2O3 catalyst was evaluated using five different sulphiding agents (carbon disulphide, dimethyldisulphide, butanethiol, thiophene and hydrogen sulphide) at high pressure (3 MPa) in the 300–450°C temperature range. The results indicate that the behaviour of the cobalt—molybdenum catalysts depends strongly on the nature of the activating molecule as well as the pretreatment temperature. The catalyst exhibited two different patterns, below and above 400°C. At 300°C, differences in the degree of sulphidation and in activities were observed when using different activating molecules. The most efficient of the sulphiding agents used was butanethiol while the least efficient one was thiophene. The activity of the catalyst was a maximum when carbon disulphide was used at 350°C or the other sulphiding agents at 400°C. We attributed the differences of effects of the various molecules to coupling effects between reduction and sulphidation reactions. Under the activation giving excellent activities, the coupling effect is optimal. Using carbon disulphide or thiophene at temperatures higher than 400°C, a catalyst with strongly decreased activity was produced. This behaviour is attributed to coke formation during sulphidation.