Crystal-Plane-Dependent Fischer-Tropsch Performance of Cobalt Catalysts

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.