Nature and reactivity of the surface species observed over a supported cobalt catalyst under CO/H2 mixtures

Abstract

The nature and reactivity of the surface species present at the surface of a Co-supported sample were investigated by in situ and operando DRIFTS. The operando DRIFTS data collected over a 15% Co/Siralox® showed that the state of the surface was typically carbon-poor under our operating conditions, i.e. the nature of the surface was metallic rather than carbidic. A significant modification of the cobalt surface was observed with time on stream. An accumulation of waxes was also noted at the catalyst surface, despite the fact that the reaction was performed at ambient pressure. Chemical transient experiments carried out by removing CO from the feed indicated that the various types of CO(ads) present (e.g. linear and bridged) displayed an apparent uniform reactivity. In contrast, two types of formates reactivity were observed, while the IR spectra of these formate species were undistinguishable. The faster reacting formates, possibly adsorbed at the interface of Co and the support or directly on an oxidic phase of cobalt, could potentially be an intermediate in the formation of the methanol side-product observed under our reaction conditions.