Chain Growth by CO Insertion in the Fischer–Tropsch Reaction

Abstract

AbstractThe molecular kinetics of the mechanism of chain growth through CO insertion of the Fischer–Tropsch reaction is analyzed. The maximum chain growth within the CO insertion chain growth model is predicted if the rate of CO activation to give the C1 species that initiates chain growth balances the rate of chain growth termination. The overall rate of chain growth, determined by the elementary rates of CO insertion, hydrogen‐transfer reaction steps, and CO bond cleavage, has to be fast compared to the rate of methanation and the rate of chain growth termination, which gives an oxygenate or hydrocarbon product. However, estimates of rate constants based on quantum‐chemical data predict low chain growth within this CO insertion mechanism, which is mainly caused by the relatively slow rate of CO insertion into the growing chain compared to the rate of product desorption. Such a high barrier for CO insertion is consistent with oxygenate formation through the carbide mechanism pathway. A comparison of the derived expressions for CO consumption shows that the rate of chain growth is limiting within the mechanism of chain growth through CO insertion, whereas within the carbide mechanism it is rate controlled by the rate of CO to CHx monomer formation.