Tailoring Carbon Deposits on a Single-Crystal Cobalt Catalyst for Fischer-Tropsch Synthesis without Further Reduction: The Role of Surface Carbon and Penetrating Carbon

The preparation of Fischer-Tropsch synthesis (FTS)catalyststhat exhibit excellent catalytic performance and are suitable fordirect use in a fixed-bed reactor without further reduction is crucialin industrial applications. However, only marginal progress has beenmade with respect to the preparation of cobalt-based FTS catalystsowing to tendency of metallic cobalt to oxidize easily; this tendencynecessitates the activation of these catalysts via reduction despitehaving undergone reduction treatment during their preparation. Herein,this problem has been addressed by tuning the carbon deposits (surfaceC and penetrating C) on the surface of a single-crystal cobalt catalyst.Screen-like surface C on a catalyst pretreated with 5% CO (p-Co-CO)exhibits diffusion suppression and chemical inertness to oxidizinggas, thus preventing the oxidation of metallic cobalt and resultingsimultaneously in high activity and low CH4 selectivity(7.2%) without requiring further reduction. Moreover, the exact roleof surface C and penetrating C deposited on cobalt catalysts in theFTS performance is explored. Both surface C and penetrating C enhancethe activity of the cobalt catalyst but with opposite effects on theFTS selectivity. Surface C improves the adsorption ability of bridged-typeCO and the formation of long-chain hydrocarbons, whereas penetratingC is conducive to adsorbing linear CO and increases undesired CH4 selectivity. This study clarifies the effect of depositedcarbon on the FTS reaction and provides insights into the design ofhigh-performance nonconventional FTS catalysts that do not requirefurther reduction.