Gas-phase and Pd-catalyzed hydrodehalogenation of CBrClF2, CCl2F2, CHClF2, and CH2F2

Hydrodehalogenation of CBrClF2, CCl2F2, CHClF2, and CH2F2 with hydrogen has been studied in the gas phase and over supported Pd catalysts in a tubular alumina reactor. During gas-phase reactions, selectivity to CH2F2 is low for the hydrodehalogenation of CBrClF2, CCl2F2, and CHClF2. CHClF2 is the primary product for the hydrodehalogenation of CBrClF2 and CCl2F2, whereas C2F4 is the major product for the hydrodehalogenation of CHClF2. Over Pd/C catalysts, CH2F2 is the primary product, with selectivities generally over 60% for the hydrodehalogenation of CBrClF2, CCl2F2, and CHClF2. Halocarbons and hydrogen compete for the available surface sites on Pd, and it is suggested that the rate-limiting step during the catalytic hydrodehalogenation of the four halocarbons involves the cleavage of C-halogen bonds, that is, C-Br in CBrClF2, C-Cl in CCl2F2 and CHClF2, and C-F in CH2F2