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

Abstract

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.

Generalized kinetic model for iron and cobalt based Fischer–Tropsch synthesis catalysts: Review and model evaluation

“…Co/MgO catalyst [28]. Though these results show close relationship between CO in gas phase and chain lengthening process, but such relationship was not observed for Co/SiO 2 [29].…”

“…It was found that there is a very close relationship between CO partial pressure in gas phase and chain lengthening on the catalyst surface [16,28,29] so it was concluded that CO in gas phase acts likely as the inserting monomer.…”

Recent Progresses in Understanding of Co-Based Fischer–Tropsch Catalysis by Means of Transient Kinetic Studies and Theoretical Analysis

“…Modeling of the response curve is less complicated although the time resolution and sensitivity is lower than for the TAP experiment. The pulse transient method has been used to study the kinetics of several key steps such as CO activation and hydrocarbon chain growth of FTS over supported cobalt catalysts [69,70].…”

CO Dissociation at Vacancy Sites on Hägg Iron Carbide: Direct Versus Hydrogen-Assisted Routes Investigated with DFT

“…A third possibility is the COinsertion mechanism, in which CO undergoes hydrogenation and C-O bond scission to form an alkyl chain initiator, followed by insertion of CO which acts as the chain propagator [8,9]. Variants of the carbide [18,19], hydroxymethylene [20,21] and CO-insertion [19,22,23] mechanisms have continued to receive support in recent times, with alternatives also having been suggested [11]. All of these mechanisms differ in the precise sequence of C-H (and C-C) bond formation and C-O bond breakage in the production of hydrocarbons from synthesis gas.…”