Tailoring Carbon Deposits on a Single-Crystal Cobalt Catalyst for Fischer–Tropsch Synthesis without Further Reduction: The Role of Surface Carbon and Penetrating Carbon
Chuan Qin, Bo Hou, Jungang Wang, Zhongyi Ma, Congbiao Chen, Litao Jia, Debao Li, Mingyue Ding
Abstract
The preparation of Fischer–Tropsch synthesis (FTS) catalysts that exhibit excellent catalytic performance and are suitable for direct use in a fixed-bed reactor without further reduction is crucial in industrial applications. However, only marginal progress has been made with respect to the preparation of cobalt-based FTS catalysts owing to tendency of metallic cobalt to oxidize easily; this tendency necessitates the activation of these catalysts via reduction despite having undergone reduction treatment during their preparation. Herein, this problem has been addressed by tuning the carbon deposits (surface C 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 oxidizing gas, thus preventing the oxidation of metallic cobalt and resulting simultaneously in high activity and low CH 4 selectivity (7.2%) without requiring further reduction. Moreover, the exact role of surface C and penetrating C deposited on cobalt catalysts in the FTS performance is explored. Both surface C and penetrating C enhance the activity of the cobalt catalyst but with opposite effects on the FTS selectivity. Surface C improves the adsorption ability of bridged-type CO and the formation of long-chain hydrocarbons, whereas penetrating C is conducive to adsorbing linear CO and increases undesired CH 4 selectivity. This study clarifies the effect of deposited carbon on the FTS reaction and provides insights into the design of high-performance nonconventional FTS catalysts that do not require further reduction.