Hydrodechlorination of CCl4 over Pt/gamma-Al2O3 - Effects of reaction pressure and diluent gases on distribution of products and catalyst stability

Pt/gamma -Al2O3 catalysts were prepared by a wet impregnation method and applied for the hydrodechlorination of CCl4 around 400 K. The extent of catalyst deactivation was in line with the propensity of the formation of oligomers (mainly C2Cl4). Both catalyst stability and selectivity to CHCl3 were enhanced when the pressure was increased up to an optimum level. Above the optimum pressure, catalyst deactivation was accelerated with enhanced dimerization of abundantly adsorbed CCl4, due to the relatively hydrogen-deficient environment on the surface. Addition of diluent gases such as CH4, N-2 improved the catalyst stability at pressurized reaction conditions. These gases adsorbed (albeit weakly) on platinum to reduce the selectivity to CHCl3, while improving the catalyst stability. The increased amount of hydrogen adsorbed on the platinum catalyst at high reaction pressures appeared to be the main factor for enhancement of selectivity to CHCl3 and catalytic stability. (C) 2001 Elsevier Science B.V All rights reservedclose281