1 1 dichloro 1 2 2 2 tetrafluoroethane is then passed through it in the molar ratios and at the flow rates and temperatures shown in the following table the last part of which collates the results obtained table 1______________________________________test no 1 2 3 4______________________________________operating conditions temperature u00b0 c 100 130 150 200molar ratio h sub 2 c sub 2 f sub 4 cl sub 2 5 5 5 5c sub 2 f sub 4 cl sub 2 flow rate mole hour 0 05 0 05 0 05 0 05results dc sub 0 of c sub 2 f sub 4 cl sub 2 4 42 97 100 s for cf sub 3 chfcl 86 84 74 50 s for cf sub 3 ch sub 2 f 9 9 13 20 s for cf sub 3 ch sub 3 4 6 13 30______________________________________ in most of the cases the selectivity for the hydrogenolysis of a single c cl bond is higher than 70 by way of comparison two tests were performed with the catalyst a according to the invention replaced with a catalyst containing 5 of palladium prepared in the same way and on the same support as in example 1 with pdcl 2 instead of ircl 3 the results collated in table 2 which follows show that with this palladium catalyst the selectivity of the reaction is clearly in favor of the abstraction of two chlorine atoms table 2______________________________________comparative test no 5 6______________________________________operating conditions temperature u00b0 c 150 200molar ratio h sub 2 c sub 2 f sub 4 cl sub 2 4 4c sub 2 f sub 4 cl sub 2 flow rate mole hour 0 07 0 07results dc sub 0 of c sub 2 f.