On the problem of cobalt chloride-based catalysts in the Fischer–Tropsch synthesis

Abstract

The role of cobalt chloride hexahydrate as a precursor of cobalt bulk catalysts for the Fischer–Tropsch reaction was studied. Applying in situ DRIFTS, in situ XANES, in situ XRD and inverse TPR, different oxygen containing cobalt compounds were detected depending on the applied parameters. Considering the different geometries of the measuring cells, the role of back mixing in the reaction network of the transformation of cobalt chloride was discussed. It was shown that only the complete removal of crystal water up to 100 °C avoids the formation of oxygen containing cobalt compounds. A reaction network was proposed to describe the transformation of cobalt chloride. The reduction of calcined cobalt chloride proceeds as a single step in the temperature range of 400–600 °C. Nitrate-based catalysts are reduced between 250 and 500 °C. The comparison of the bulk cobalt catalysts prepared either with cobalt nitrate or cobalt chloride showed a strong influence on the degree of conversion in the Fischer–Tropsch reaction. The difference in activity was explained in terms of residual chloride ions on the catalyst surface. Consequently, the activation procedure of the cobalt chloride-based catalysts must be chosen carefully to force the formation of cobalt oxide.