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

Pt/γ-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, N₂ 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.