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Site poisoning is a powerful method to unravel the nature of active sites or reaction intermediates. The nature of the intermediates involved in the hydrogenation of CO was unraveled by poisoning alumina-supported cobalt catalysts with various concentrations of tin. The rate of formation of the main reaction products (methane and propylene) was found to be proportional to the concentration of multi-bonded CO, likely located in hollow sites. The specific rate of decomposition of these species was sufficient to account for the formation of the main products. These hollow-CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions used here, while linear CO are mostly spectators. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]