Hydrodechlorination of CHClF2 (HCFC-22) over Pd-Pt Catalysts Supported on Thermally Modified Activated Carbon

Commercial activated carbon, pretreated in helium at 1600 degrees C and largely free of micropores, was used as a support for two series of 2 wt.% Pd-Pt catalysts, prepared by impregnating the support with metal acetylacetonates or metal chlorides. The catalysts were characterized by temperature-programmed methods, H-2 chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with energy dispersive spectroscopy (EDS). Overall, the results confirmed the existence of well-dispersed Pd-Pt nanoparticles in the bimetallic catalysts, ranging in size from 2 to 3 nm. The catalysts were investigated in the gas phase hydrodechlorination of chlorodifluoromethane (HCFC-22). In this environmentally relevant reaction, both the ex-chloride and ex-acetylacetonate Pd-Pt/C catalysts exhibited better hydrodechlorination activity than the monometallic catalysts, which is consistent with the previous results of hydrodechlorination for other chlorine-containing compounds. This synergistic effect can be attributed to the electron charge transfer from platinum to palladium. In general, product selectivity changes regularly with Pd-Pt alloy composition, from high in CH2F2 for Pd/C (70-80%) to the selective formation of CH4 for Pt/C (60-70%).