Hydrocarbon Chain Lengthening in Catalytic CO Hydrogenation: Evidence for a CO-Insertion Mechanism

We studied CO hydrogenation over Co/MgO (10/1) model catalysts using chemical transient kinetics. Quantification of the time-dependent response during fast changes of the gas flow composition enabled the counting of surface amounts of carbon, oxygen, and hydrogen from the onset of adsorption to the steady state of the reaction and vice versa. Under the atmospheric pressure conditions of the reaction, the total amount of adsorbed species exceeded the monolayer limit on Co metal. The time response in transients and back-transients of gaseous reactants and products is in accordance with a CO insertion mechanism. Furthermore, the Anderson-Schulz-Flory chain lengthening probability is directly proportional to the CO pressure, whereas no such dependence is measured for the amounts of accumulating or fading surface carbon.