Utilization of nonprecious transition metals for high alcohols synthesis is of a great importance in heterogeneous catalysis. We synthesized successfully cobalt metal-carbide (Co− Co 2 C) catalysts, which present remarkable activity and selectivity for high alpha-alcohols via the Fischer−Tropsch reaction. The formation of the stable cobalt carbide and the Co−Co 2 C interface are found to be essential for the observed reactivity. Density functional theory calculations show that Co 2 C is highly efficient for CO nondissociative 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 hydrocarbon, could be used to rationalize the design of the nonprecious transition metal catalysts for the oxygenates in syngas conversion.

Cobalt carbide (Co2C) has recently been reported to be efficient for the conversion of syngas (CO+H2) to lower olefins (C2–C4) and higher alcohols (C2+ alcohols); however, its properties and formation conditions remain ambiguous. On the basis of our previous investigations concerning the formation of Co2C, the work herein was aimed at defining the mechanism by which the manganese promoter functions in the Co-based catalysts supported on activated carbon (CoxMn/AC). Experimental studies validated that Mn facilitates the dissociation and disproportionation of CO on the surface of catalyst and prohibits H2 adsorption to some extent, creating a relative C-rich and H-lean surface chemical environment. We advocate that the surface conditions result in the transformation from metallic Co to Co2C phase under realistic reaction conditions to form Co@Co2C nanoparticles, in which residual small Co0 ensembles (<6 nm) distribute on the surface of Co2C nanoparticles (∼20 nm). Compared with the Co/AC catalyst, where the active site is composed of Co2C phase on the surface of Co0 nanoparticles (Co2C@Co), the Mn-promoted catalysts (Co@Co2C) displayed much higher olefin selectivity (10% versus 40%), while the selectivity to alcohols over the two catalysts are similar (∼20%). The rationale behind the strong structure–performance relationship is twofold. On the one hand, Co–Co2C interfaces exist universally in the catalysts, where synergistic effects between metallic Co and Co2C phase occur and are responsible for the formation of alcohols. On the other hand, the relative C-rich and H-lean surface chemical environment created by Mn on the Co@Co2C catalysts facilitates the formation of olefins.

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