The Influence of the Compacting Condition on the Activity and the Structure of Co-Mo-Al2O3 Catalyst

The influence of pelletizing conditions on the catalytic activity of a Co-Mo-Al2O3 catalyst was studied using the hydrogenolysis of thiophene as a test reaction. In this experimental work, the catalyst was compressed under a pressure (P) of 500∼7, 000kg/cm2 at a temperature of either 60°C or 80°C. The catalytic activity of the resultant catalyst was measured with a conventional flow type apparatus at a temperature of 375∼450°C. The experimental results were analyzed by a conventional rate equation, and the apparent activation energy (E) as well as the frequency factor (A) were obtained. Further, the specific surface areas (Σ), pore size distributions, and the lattice distances (d) of the catalyst were measured.According to the experimental results, the maximum activity appeared at P_??_1, 000kg/cm2 when the catalyst was compressed at 60°C, while the maximum activity appeared at P_??_2, 000kg/cm2 when the catalyst was compressed at 80°C. A similar maximum was observed on the Σ-P curve. Thus, it was considered that a change in the surface area of the catalyst resulted in a change in catalyst activity. On the other hand, the effects of pore diffusion on the catalytic activity were thought to be insignificant, even though a considerable decrease in pore size was found to take place on compression of the catalyst. The increase in the catalytic activity per unit surface area served as evidence of this view.A more interesting fact observed in this work was the change in the lattice distance (d). Two discontinuities were observed on the d-P curve. Further, the apparent activation energy (E) varied discontinuously at the compacting pressures where the lattice distance varied abruptly. From this fact it was considered that the change in the crystal structure of the catalyst surface also contributes to the activity change due to compression.