Identification of body-centred cubic cobalt and its importance in CO hydrogenation

Abstract

THE Fischer–Tropsch reaction, involving the hydrogenation of CO to form hydrocarbons and their oxygenated derivatives, is a catalytic process of considerable industrial importance. We have recently1 studied the process using cobalt/manganese oxide catalysts, and have investigated the nature of the working catalysts under realistic synthesis conditions. Here we report on in situ X-ray diffraction studies of the bulk structure of the catalyst during reduction with hydrogen and subsequent hydrogenation of CO. We identify the formation of a body-centred cubic (b.c.c.) phase of metallic cobalt during the process. This phase, unknown until recently and never before prepared in bulk, is metastable; it reverts to the stable face-centred cubic structure after exposure to air and slight pressure at room temperature. The body-centred cubic structure may have a significant influence on the hydrocarbon selectivities of cobalt-containing catalysts.