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International audience; Fischer-Tropsch synthesis is a major part of XTL (X-To-Liquids, with X = Gas, Biomass or Coal) technologies, which converts syngas into clean hydrocarbon fuels. Cobalt catalysts supported by inorganic oxides appear to be a reasonable compromise for the synthesis of long-chain paraffins and waxes. The efficiency of Fischer-Tropsch technology strongly depends on the performance of cobalt catalysts. Promotion of cobalt catalysts with noble metals results in a significant increase in Fischer-Tropsch catalytic activity. This paper reviews different effects on the structure and catalytic performance of cobalt supported Fischer-Tropsch catalysts which arise from the promotion with noble metals. Both catalytic performance and catalyst cost seem to be major criteria in the design of efficient cobalt Fischer-Tropsch catalysts.

Structural Modification of Cobalt Catalysts: Effect of Wetting Studied by X-Ray and Infrared Techniques — The effect of wetting on the structure and localisation of cobalt species on various supports (Al 2 O 3 , SiO 2 , TiO 2 , HZSM-5 zeolite) was studied using X-ray diffraction, Fourier transform infrared spectroscopy with CO as a molecular probe, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis. Aqueous impregnation to incipient wetness of reduced and passivated cobalt catalysts results, even in the absence of any promoter, in a considerable decrease in the concentration of Co crystalline phases and modifies the surface sites. The decrease in the concentration of Co 3 O 4 crystallites was especially pronounced on silica supported catalysts prepared via impregnation of cobalt and on a mixture of Co 3 O 4 and HZSM-5 zeolite. Saturation with water of the passivated Co/SiO 2 sample results in an amorphous solid with a local structure close to that of Co 2 SiO 4 . For Co/Al 2 O 3 and Co/TiO 2 catalysts, the effect of wetting on the concentration of Co 3 O 4 crystalline phase was considerably smaller.