First-principles study of structure sensitivity of chain growth and selectivity in Fischer-Tropsch synthesis using HCP cobalt catalysts

摘要

Structure sensitivity on chain growth and selectivity in cobalt catalyzed Fischer-Tropsch synthesis (FTS) were studied by density functional theory (DFT) calculations. It is found that at a lower CO coverage, chain growth tends to proceed via a CO insertion mechanism on close-packed Co (0001) and stepped Co, with CH4 as the main product. However, a carbide mechanism is preferable on more open Co (1011) accompanied with higher selectivity to C-2 hydrocarbons than CH4. The origin is identified from the structure sensitive adsorption of the key intermediates, specifically the least "saturated" C/CH species, which exhibit a relatively strong dependence on the structure evolution. With increasing CO coverage, the CO insertion mechanism becomes more favorable, and both FTS activity and C-2 hydrocarbon selectivity increase on Co (0001). This work highlights the intrinsic structure and coverage effects, achieving fundamental insight that can potentially be used to design and develop improved catalysts for FTS and other important reactions in syngas conversion.