Conversion of CCl2F2 (CFC-12) in the presence and absence of H-2 on sol-gel derived Pd/Al2O3 catalysts

Conversion of CCl2F2 in the presence (hydrogenolysis) and absence of hydrog en was investigated on Al2O3, AlF3 and Pd/Al2O3 xerogel and aerogel catalys ts. CCl2F2 was found to form CClF3 and CCl3F on Al2O3 and AlF3 in the prese nce and absence of hydrogen as well as on the Pd/Al2O3 catalysts in the abs ence of hydrogen. Overall activity increased during the hydrogenolysis reac tions at 230 degrees C as a function of time which was paralleled by a sign ificant increase in the yield of CClF3 formed through a Cl/F-exchange react ion. X-ray diffraction patterns of thr spent catalyst recovered after 3 h o f hydrogenolysis confirmed the presence of Pd(C) (Pd-carbon solid solution) and AlF3 phases on Pd/Al2O3 catalysts indicated that the carbon incorporat ion into the Pd lattice and the transformation of Al2O3 to AlF3 starts at t he initial stage of the reaction. It was concluded that AlF3 is responsible for the Cl/F-exchange reactions. CH4, a complete hydrogenation product, is formed during hydrogenolysis. Another route for its formation is the react ion between hydrogen in the gas phase and the interstitial carbon. (C) 1999 Elsevier Science B.V. All rights reserved.