Palladium-catalyzed hydrogenation without hydrogen: the hydrodechlorination of chlorofluorocarbons with solid state hydrogen over the palladium(111) crystal surface and its implications

The hydrogenation of chlorofluorocarbons (CFC's, 1,1-dichlorotetrafluoroethane, CCl2F-CF3) was found to be positive 1/2 order in hydrogen pressure over palladium foil while it was zero order in hydrogen pressure over palladium single crystals regardless of their orientation ((111), (100)). When hydrogen was completely removed from the gas phase, hydrogenation continued for about 10(4) turnovers over palladium single crystals which were pre-exposed to hydrogen. Solid state hydrogen, stored in the bulk of a palladium single crystal, was found to be responsible for the hydrodechlorination of CCl2 F-CF3 in the absence of gas phase hydrogen. Lower reaction rates and increased selectivity for overhydrogenation to produce CH3-CF3 indicate that the nature of hydrogenation with solid state hydrogen in palladium is different from hydrogenation with gas phase hydrogen. The use of solid state hydrogen for various chemical processes instead of gas phase hydrogen has advantages that are enumerated.