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The effect of alkali impurities on Co-based Fischer-Tropsch (FT) catalysts is important for processing biomass-derived synthesis gas containing inorganic ash impurities. The effects of Na, K, Li, and Ca impurities on c-Al 2 O 3 -supported Co-Re powder catalysts were studied at impurity loadings between 25 and 1,000 ppm. Impurity addition did not have any effect on H 2 chemisorption, but the catalyst activity decreased during FT synthesis experiments. The impurities were also found to slightly increase the reduction temperatures of Co. Carbon selectivities to CH 4 decreased with increasing impurity loading, while CO 2 and C 5? hydrocarbon selectivities increased. Catalyst behavior was attributed mostly to electronic effects from the alkali addition, leading to decreased surface H concentrations and increased CO adsorption and dissociation.

The hierarchically structured carbon nanofibers (CNFs)/carbon felt composites, in which CNFs were directly grown on the surface of microfibers in carbon felt, forming a CNF layer on a micrometer range that completely covers the microfiber surfaces, were tested as a novel support material for cobalt nanoparticles in the highly exothermic Fischer-Tropsch (F-T) synthesis. A compact, fixed-bed reactor, made of disks of such composite materials, offered the advantages of improved heat and mass transfer, relatively low pressure drop, and safe handling of immobilized CNFs. An efficient 3-D thermal conductive network in the composite provided a relatively uniform temperature profile, whereas the open structure of the CNF layer afforded an almost 100 % effectiveness of Co nanoparticles in the F-T synthesis in the fixed bed. The greatly improved mass and heat transport makes the compact reactor attractive for applications in the conversion of biomass, coal, and natural gas to liquids.