Bulk and surface characterization of supported cobalt–copper catalysts active in CO hydrocondensation

Abstract

We report the results of the characterization of three cobalt–copper catalysts, supported respectively on MgO, CeO₂ and ZrO₂ and exhibiting different selectivity behaviour in the production of higher alcohols from synthesis gas. The local composition of the catalyst has been analysed by STEM and the surface state studied by FTIR spectroscopy of adsorbed CO. The results deduced from the STEM analysis show that each metallic particle has a global composition close to the nominal one. By contrast, i.r. data indicate large changes in surface compsition and chemical state. Thus, the surface is constituted for metallic cobalt for the CoCu/CeO₂ system, principally of copper when the support is MgO, but is composed of both metallic cobalt and copper for the Co–Cu/ZrO₂ catalyst. These results are discussed in relation to the catalytic properties, In particular, it seems that a high selectivity in higher alcohols requires metallic sites constituted of both cobalt and copper.