Selectivity modulation in Fischer-Tropsch synthesis through reducibility control of cobalt-species containing HMS framework

Abstract

Here reports the modulation of selectivity in Fischer-Tropsch synthesis through the control of cobalt reducibility within a hexagonal mesoporous silica (HMS) framework. Cobalt loading, varied from 3 % to 12.5 wt%, generated different surface and bulk cobalt species that interact variably with the support, significantly influencing their reducibility and the resultant catalytic behavior. This variation significantly affected the reducibility of the cobalt species, influencing on the catalytic behavior. The control of reducibility and stability of Co species is contingent on the cobalt loading. Higher cobalt content enhances the reducibility of Co species, shifting product selectivity from long-chain hydrocarbons to lighter olefins and oxygenates. At a TOS of 4 h, the active phase predominantly involves metallic Co species, while CO₂ and oxygenates formation is closely linked to the pair Co⁰-Co²⁺ active phase. After a TOS of 120 h, samples with higher cobalt content (6.1–15.8 % wt.) exhibited notable deactivation and changes in selectivity and hydrocarbon distribution. These changes were associated with the formation of a Co₂C phase, which inhibits methane formation and chain growth while enhancing the production of lower olefins and oxygenates through a synergistic interaction at the Co⁰ and Co₂C interface, also improves the WGS reaction, thereby increasing CO₂ selectivity.