Catalytic Hydrodechlorination of 1,1-Dichlorotetrafluoroethane by Pd/Al 2 O 3

Author： Karpinski Z. Early K. d'Itri J.L.

ISSN： 0021-9517

Source： Journal of Catalysis, Vol.164, Iss.2, 1996-12, pp. : 378-386

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Abstract

Palladium supported on gamma-alumina displays high activity for the hydrodechlorination of 1,1-dichlorotetrafluoroethane. High H 2 partial pressures are needed to avoid deactivation, and steady state is obtained after =~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 CF 3 CFH 2 . 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#°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 .