Catalytic removal of chlorine from organic compounds.

Several carbon-supported, bimetallic palladinum-gold systems were prepared and screened as catalysts for the hydrodechlorination of dichlorodifluoromethane (CFC-12). Since catalytic behavior depends very much on the extent of Pd-Au alloying, it was necessary to ensure proper conditions for mutual interaction of both alloy components after their deposition on the support. The direct redox reaction, which involves a reductive deposition of gold ions on pre-reduced palladinum material appeared very useful. Characterizing these catalysts by x-ray diffraction and other methods showed a higher degree of Pd-Au interaction than that in Pd-Au/C catalysts prepared by impregnation. Kinetic studies indicated an intimate contact of Pd and Au is essential to improve selectivity to difluoromethane (from ~70% for Pd/C to ~90% for Pd-Au/C catalysts prepared by direct redox method). Large amounts of carbon originated from the CFC-12 molecule enter palladinum lattice during hydrodechlorination. During reaction part of this carbon can be hydrogenated from the catalyst, giving rise to higher selectivity towards methane. Well-mixed, highly selective toward CH2F2, Pd-Au catalysts absorb much less carbon.