Characterization and testing of silica-supported cobalt–palladium catalysts for conversion of syngas to oxygenates

Silica-supported Co–Pd catalysts were prepared by co-impregnation using 2 wt% Pd and two different cobalt loadings: 2 wt% (2Co–2Pd) and 10 wt% (10Co–2Pd). They were characterized by ICP-OES, H2-TPR, in situ XRD, DRIFTS, and activity/selectivity in CO hydrogenation. Activity/selectivity studies showed that the 10Co–2Pd catalyst is more active for CO hydrogenation with high selectivity toward hydrocarbons, while 2Co–2Pd catalyst shows higher selectivity toward oxygenates, but considerably lower overall activity. DRIFTS studies for 10Co–2Pd catalyst at 230 °C indicated that sites at which CO adsorbs linearly are the main active sites for CO hydrogenation, which leads toward formation of hydrocarbons. On the other hand, the bridged sites were found to be the main active sites for 2Co–2Pd catalyst, which leads to increased selectivity toward oxygenated compounds. The hydrogenation of CO adsorbed on these bridge sites was found to be much slower, explaining the low activity of this catalyst.

DRIFTS investigation of CO hydrogenation on cobalt–palladium catalysts showed different active sites for catalysts with different cobalt loadings. Linearly adsorbed CO was found to be the main active species leading towards hydrocarbon formation on 10Co–2Pd catalyst. On the other hand, bridged sites were found to be the main active sites for 2Co–2Pd catalyst, leading towards increased oxygenates selectivity.Figure optionsDownload high-quality image (95 K)Download as PowerPoint slideHighlights
► Palladium promotion increases the reducibility of silica supported cobalt catalysts.
► Close contact between Co and Pd is needed for high selectivity toward oxygenates.
► Bridging CO sites are found to be the active sites for oxygenates.
► Terminal CO sites lead to the formation of hydrocarbons.
► Hydrogenation of terminal CO is much faster than the bridge-type adsorbed CO.