Dynamics of Co/Co2C redox cycle and their catalytic consequences in Fischer–Tropsch synthesis on cobalt–manganese catalysts

Fischer–Tropsch synthesis over CoMn oxides is a surface-catalyzed structure-sensitive reaction. Active site changes greatly alter product distribution. The dynamics and essence of the changes in Co species during the reaction have seldom been explored. Herein, multiple characterizations were applied to confirm that two types of active sites, i.e., Co and Co 2 C, coexist on CoMnO x under the reaction conditions. Apart from the direct participation of carbon species in the reaction, the steady-state isotopic transient kinetic analysis also suggested the mutual transformation of carbon species in Co 2 C. The ratio of the two paths altered with the temperature, thus leading to Co 2 C-rich and Co-rich surfaces at intermediate and high temperatures, respectively. Kinetic calculations and microkinetic modeling showed that Co 2 C-rich surfaces facilitated CO adsorption and suppressed hydrogen adsorption. This gave high carbon-chain growth activity. The Co-rich surfaces showed high vacancy and hydrogen coverages, lowering the CO activation and CH 4 formation energies.