(336c) An Investigation into the Effect of Li and Mn Promotions on the Activity and Selecivities to Olefins and Alcohols of Co@Co2C/Activated Carbon (AC) for Fischer-Tropsch Reaction

Utilization of non-precious transition metals for high alcohols and olefins synthesis is of a great importance in heterogeneous catalysis. We synthesized successfully Li and Mn promoted AC supported cobalt metal-carbide (Co@Co₂C/AC) catalysts, which present remarkable activity of more than 200g/kg-cat.h and selectivities of ca. 65 C% both for alpha-alcohols and alpha-olefins via the Fischer-Tropsch reaction at the mild conditions. The formation of the stable cobalt carbide and the Co@Co₂C interface are found essential for the observed reactivity. The results of characterization from In-situ EXAFS, in-situ XRD, HRTEM, XSP, and chemo-adsorption of H₂ and CO experiments showed that Mn promotes the formation of Co₂C species during Fischer-Tropsch reaction and Li increased the CO uptake, while both promoters have little impact on the amount of H₂ uptakes. Density functional theory calculations show that Co₂C is highly efficient for CO non-dissociative adsorption, behaving as noble-metal-like, whereas the Co metal is highly active for CO dissociative adsorption and the subsequent carbon-chain growth. The interface between the cobalt metal and its carbide phase as well as the dual sites available at the interface for facile CO insertion to C_nH_m-groups formed on the Co sites. The remarkably high alpha-alcohol and alpha-olefins selectivities from the Li and Mn promotion effects, namely the formation of more interfacial active sites between Co and Co₂C and enhancement of the ratio for chemo-adsorption CO to H₂ uptake on the surface of Co@Co₂C/AC catalysts, paves a new way for the design of the new catalysts for synthesizing various high value-products in syngas applications.