Hydrodechlorination of dichlorodifluoromethane, carbon tetrachloride and 1,2-dichloroethane over Pt/Al2O3 catalysts

Abstract

A comparative study of hydrodechlorination of dichlorodifluoromethane, carbon tetrachloride and 1,2-dichloroethane over alumina-supported Pt catalysts showed several interesting features in the catalytic behavior. Platinum proved to be very good catalyst in CCl4 hydrodechlorination (with high selectivity toward CHCl3), whereas for CCl2F2 and 1,2-dichloroethane hydrodechlorinations this metal exhibits rather low activity and, in addition, converts the reactants to less valuable products (e.g. alkanes). However, a rapid deactivation of Pt catalysts during hydrodechlorination requires their frequent regeneration. Two regeneration protocols tested in this work showed interesting, albeit somewhat different, activity evolutions. Removal of chlorine species by hydrogen at 350 °C led to a moderate increase of catalytic activity. On the other hand, a partial removal of carbonaceous residues by oxidative pretreatment brought about a considerable increase of the overall conversion level in CCl4 hydrodechlorination. Additional temperature-programmed experiments with spent and regenerated Pt/Al2O3 catalyst suggest that a partial removal of carbonaceous deposit (most probably followed by its reconstruction) leading to the formation of very active catalyst, less susceptible to poisoning by chlorine.