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The effect of water on the activity and selectivity for a series of c-Al 2 O 3 supported cobalt Fischer-Tropsch catalysts has been studied in an isothermal fixed-bed reactor at T=483 K, P=20 bar, and H 2 /CO=2.1. The catalysts were produced applying incipient wetness impregnation and consisted of 20 wt.% cobalt and 0.5 wt.% rhenium deposited on c-Al 2 O 3 supports with different pore characteristics. For the narrow-pore catalysts, addition of water corresponding to an inlet partial pressure ratio of P H2 O/P H2 =0.4 reduced the reaction rates. In contrast, for a catalyst with larger pores the same water pressure increased the reaction rates. For all catalysts, water amounts equal to P H2 O/P H2 =0.7 at the reactor inlet suppressed the reaction rates and led to permanent deactivation. The addition of water increased the C 5+ selectivity and decreased the CH 4 selectivity for all catalysts. The pore characteristics seem to determine the effect of water on the rates.

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Platelet and fishbone carbon nanofibers (CNFs) have been used as supports for cobalt Fischer-Tropsch catalysts. The activity and selectivity of the CNF supported catalysts have been studied at 483 K, 20 bar, and H 2 /CO = 2.1, and compared with corresponding activity and selectivity for a-Al 2 O 3 and c-Al 2 O 3 supported cobalt catalysts. The platelet CNF supported catalyst has demonstrated high activity and high selectivity to C 5+ hydrocarbons, with activity comparable with Co/c-Al 2 O 3 and selectivity comparable with Co/a-Al 2 O 3 .

Resistance towards attrition, sufficient activity at end-of-run and high selectivity to desired products are some of the requirements for a slurry Fischer-Tropsch catalyst. We have found that modifying an alumina support by 2-valent metals, including magnesium, nickel and zinc, followed by high temperature firing, results in superior mechanical and 'chemical attrition' (dissolution) resistance of the catalyst. Further, a sufficiently high surface area is being stabilized. The catalyst performance has been verified in a long term test in a semi-commercial plant, including very good wax separation and high wax purity. Combined with appropriate process conditions, stable longterm operation of the catalyst is secured.