Identification of the crystal plane effect of the Co derived from Co3O4 nanocrystals (NCs) on Fischer–Tropsch synthesis (FTS) is important for developing high-performance FTS solid catalysts. However, the achievement of this goal is hindered by the complexity of the FTS and the absence of sufficient crystallographic structure data. In this study, we report that the experimental FT performance of the Co catalysts depends on the exposed crystal facets of the Co3O4 NCs. The exposed Co3O4 NC {112} facets have the highest catalytic activity and the lowest methane selectivity (6.2%) in comparison to those of the {111} and {001} planes. The evolution of the crystal planes during the reduction was investigated further, and the preferred orientation relationship induced by the Co3O4 → Co transformation was {112} → {10–11}, {111} → {0001}, and {001} → {11–20}. CO temperature-programmed surface reaction experiments and density functional theory calculations further verified that the high FT performance of Co3O4{112} can be attributed to the specific surface topology of its active phase (i.e., Co{10–11}). Our findings clarify that the activity and selectivity of the FTS reaction can be enhanced by the selective exposure of a specific crystal plane from Co3O4 and could open an avenue for the rational design of high-performance FTS catalysts.

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A comprehensive density functional theory (DFT) calculation of C 2 hydrocarbons formation in Fischer− Tropsch synthesis (FTS) on the close-packed fcc-Co(111) surface has been carried out. The activation barriers and reaction energies for CO dissociation, CH x hydrogenation, CH x + CH y coupling and C(HO) insertion into CH x , CH x CH y −O bond scission, and successive hydrogenation reactions involved in C 2 hydrocarbons formation have been examined, and the following conclusions could be concluded: (i) CH is the dominant monomer, which is formed via CO + H → CHO → CH + O; (ii) CHO insertion is more plausible for C−C chain formation compared with CO insertion and CH x −CH y coupling. The rate-determining steps for C 2 hydrocarbons are CO + H → CHO and CHCH + H → CH 2 CH. Meanwhile, CH 3 hydrogenation to form CH 4 is more facile than C 2 hydrocarbons, which will lead to the low productivity and selectivity to C 2 hydrocarbons. (iii) Stepped-Co(111) surface has been modeled to clarify the role of defects during C 2 hydrocarbons formation, and the calculation results indicate that CHO and CH 2 CH formation could be facilitated and CH 4 formation could be suppressed, suggesting that the step sites could effectively promote the catalytic activity and selectivity for C 2 hydrocarbons formation.

A series of core–shell‐structured catalysts that consist of different‐sized Co3O4 nano‐particles and silica shells were prepared by an in situ coating method. The reduced catalysts displayed uniform core sizes that ranged from 5.5–12.7 nm as ascertained by TEM, which concurred well with XRD analysis. The BET results revealed the highly mesoporous nature of the silica shell, which contributes to the facile access of the reactant gas to the active sites on the core particles. The degree of reduction of the calcined catalysts studied by H2 temperature‐programmed reduction was enhanced with increased Co particle size. In the Fischer–Tropsch synthesis, a volcano‐like curve was plotted as the CO conversion and Co‐time‐yield revealed a rapid growth if the particle size increased from 5.5 to 8.7 nm and then decreased with further increased particle size to 12.7 nm, which is an effect of the combination of Co dispersion and reducibility. However, the turnover frequency remained invariant for catalysts with particle sizes larger than 8.7 nm. If we consider the product selectivity, generally, larger particles led to a longer chain length of hydrocarbons with a larger chain‐growth probability. The selectivity towards methane decreased and the corresponding heavy hydrocarbons (C19+) increased continuously with the increase of particle size. The catalyst with a particle size of 8.7 nm exhibited the highest selectivity and the maximum space‐time‐yield towards middle distillates (C5–C18) because of the modest chain‐growth probability.