The Nature of the Active Phase in Iron Fischer-Tropsch Catalysts

摘要

Fischer-Tropsch Synthesis is recognized as a viable route for conversion of syngas (derived from coal or natural gas) to liquid fuels (1). Due to their high water gas shift activity. Fe catalysts are the preferred choice for coal derived syngas having a H_2/CO ratio <1. This study is directed at understanding the mechanisms of catalyst deactivation. It is recognized that loss of surface area of the catalystically active phase and deposition of unreactive carbonaceous deposits may constitute possible mechanisms for catalyst deactivation (2). However, there is as yet no consensus in the literature on the nature of the active phase in Fe F-T catalysts. In order to get accurate phase information of working FTS catalysts, and to minimize problems with surface oxidation of the reduced iron phases, we feel it is necessary to characterize working iron catalysts protected by the hydrocarbon wax (3). The low catalyst loading in the wax makes analysis difficult, in addition the hydrocarbon wax can be crystalline, interfering with the XRD peaks from the Fe phases of interest (3). In this study, we have used an alternative procedure where most of the wax is extracted using a toluene solvent at ambient temperature. The catalyst was analyzed by x-ray diffraction and complementary information was obtained via cross-section transmission electron microscopy (XTEM). These catalysts were also analyzed by Mossbauer spectroscopy and those results will be reported elsewhere (4).