Catalyst deactivation in the selective hydrogenolysis of CCl2F2 into CH2F2

The stability of 1 wt% palladium on activated carbon catalyst in the selective hydrogenolysis of CCl2F2 into CH2F2 as function of temperature (510-540 K) and of hydrogen to CCl2F2 feed ratio (1.5-20 mol/mol) has been studied. A stable catalyst performance for at least 1600 h of operation has been obtained at 510 K and H-2 to CCl2F2 feed ratios of 6 and 10. At lower ratio (1.5 to 3) a continuous deactivation of the catalyst was observed. A H-2 to CCl2F2 ratio of >20 led also to deactivation of the catalyst. Both the conversion of CCl2F2 and the selectivity for CH2F2 were higher at increasing ratio. These differences in catalyst performance became more pronounced as a function of time on stream The observed phenomena of deactivation could be well explained by the formation of carbonaceous deposits on the catalyst surface. Neither sintering nor loss of palladium was found to play a role in deactivation. On the contrary, the used catalysts had a higher palladium dispersion than the fresh catalyst. The degree of dispersion depended on the H-2 to CCl2F2 feed ratio and temperature.