Conversion of CCl 2F 2 (CFC-12) in the presence and absence of H 2 on sol–gel derived Pd/Al 2O 3 catalysts

Abstract

Conversion of CCl 2F 2 in the presence (hydrogenolysis) and absence of hydrogen was investigated on Al 2O 3, AlF 3 and Pd/Al 2O 3 xerogel and aerogel catalysts. CCl 2F 2 was found to form CClF 3 and CCl 3F on Al 2O 3 and AlF 3 in the presence and absence of hydrogen as well as on the Pd/Al 2O 3 catalysts in the absence of hydrogen. Overall activity increased during the hydrogenolysis reactions at 230°C as a function of time which was paralleled by a significant increase in the yield of CClF 3 formed through a Cl/F-exchange reaction. X-ray diffraction patterns of the spent catalyst recovered after 3 h of hydrogenolysis confirmed the presence of Pd(C) (Pd–carbon solid solution) and AlF 3 phases on Pd/Al 2O 3 catalysts indicated that the carbon incorporation into the Pd lattice and the transformation of Al 2O 3 to AlF 3 starts at the initial stage of the reaction. It was concluded that AlF 3 is responsible for the Cl/F-exchange reactions. CH 4, a complete hydrogenation product, is formed during hydrogenolysis. Another route for its formation is the reaction between hydrogen in the gas phase and the interstitial carbon.