Catalytic hydrodechlorination of 1,1-dichlorotetrafluoroethane by Pd/Al2O3

Palladium supported on gamma-alumina displays high activity for the hydrodechlorination of 1,1-dichloratetrafluoroethane. High H-2 partial pressures are needed to avoid deactivation, and steady state is obtained after similar to 5 h time on stream. Under these conditions (H-2/CFC feed ratio = 20) the reaction is zero order in H-2 partial pressure and positive (0.65) order in 1,1-dichlorotetrafluoroethane partial pressure. Three main products are formed: 1,1,1,2-tetrafluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, and 1,1,1-trifluoroethane, with approximately 85% selectivity toward the desired CF3CFH2. The apparent activation energies associated with the formation of each product range from 52 to 68 kJ/mol. All three major products have a nonzero rate of formation in the limit of zero conversion, the implication of which is that all are primary products. The kinetics results are consistent with a reaction mechanism involving a carbene intermediate. Variation of the temperature at which the catalyst is prereduced from 300 to 600 degrees C results in an increase in particle size from 11-53 nm and in an increase in the hydrodechlorination TOF from 2.3 to 5.0 s(-1). (C) Academic Press Inc.