A kinetic treatment of the gas phase hydrodechlorination of chlorobenzene over nickel/silica: beyond conventional kinetics

The gas phase hydrodechlorination of chlorobenzene over the temperature range 473 K less than or equal to T less than or equal to 573 K has been studied using a 1.5% w/w Ni/SiO2 catalyst. The catalyst was fully selective in promoting dechlorination where benzene and HCl were the only detected products and there was no evidence of any catalyst deactivation. Reproducible dechlorination rates are provided and the effects of varying both chlorobenzene (0.02-0.1 atm) and hydrogen (0.35-0.95 atm) partial pressures at various reaction temperatures are presented to generate a database of 108 experimental entry values. The suitability of several kinetic expressions, based on reaction mechanisms that have been advanced in the literature, to represent the experimental data was assessed. On the whole, each mechanistic model provided an adequate fit to the entire experimental dataset but appreciable deviations of the predicted from the actual dechlorination rates were observed under certain reaction conditions. These deviations have allowed us to discriminate between the various mechanistic models and have facilitated a degree of model refinement. The best description was obtained for models featuring surface reaction between non-competitively and dissociatively adsorbed chlorobenzene and spillover hydrogen where the latter was viewed as adsorbed on a non-uniform surface. (C) 2001 Elsevier Science Ltd. All rights reserved.