CONVERSION UNDER HYDROGEN OF DICHLORODIFLUOROMETHANE OVER BIMETALLIC PALLADIUM CATALYSTS

The conversion of difluorodichloromethane under hydrogen has been studied in the ps phase between 413 and 473 K at atmospheric pressure over graphite supported Pd, PdK, PdFe, PdCo and PdAg catalysts reduced at 523 K. Neither a stoichiometric phase, nor a solid solution was detected in these catalysts. In CF2Cl2 hydrogenation at low CF2Cl2 pressure (P(CF2Cl2) /P(H2) < 0.3), CH2F2 and CH4 represent more than 95% of the products. However, at high CF2Cl2 Pressure (P(CF2Cl2)/P(H2) > 2), and over PdFe/graphite or PdCo/graphite catalysts, high selectivities for the coupling product CF2CF2 were obtained. This is probably due to the occurrence of some mixed sites between Pd and Fe or Co. The kinetics of the reaction indicates adsorption competition between CF2Cl2 and H-2 for the active sites, which can be described by an halogenation/dehalogenation mechanism of the palladium surface by CF2Cl2 and hydrogen respectively.