Halogen Free Methods for Catalysts Regeneration

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ABSTRACT CTS-9502141 This effort lays the basis for replacing chlorine used for redispersion of supported metal catalysts with a (-diketone. Previous work has shown that (-diketones react with transition metals and their oxides to form (-diketonates, and that these can be reduced back to active catalysts. Preliminary experiments suggest that platinum on alumina can be redispersed by treatment with hexafluoro-2,4-pentanedione (hfac). The present study examines the redispersion process in detail. Transmission electron microscopy (TEM) is used to determine if redispersion goes through an etching, mechanism or a spreading mechanism. Temperature-programmed desorption (TPD) is used to examine the interaction of (-diketones with metal surfaces and supports, including the variation of binding energy with nature of the ligand. Spectroscopic and TPD measurements are correlated with redispersion rates. Studies are done on both model catalysts and real industrial catalysts. Current practice uses chlorine to redisperse supported metal catalysts. While this process is regarded as technologically and economically satisfactory, it has some environmental drawbacks relating both to release of chlorine to the atmosphere and the formation of chlorinated dioxins from chlorine residues left on the catalyst. The approach investigated there avoids both of these problems, and may do so without any loss of effectiveness. ***