The new role of pivotal intermediate CH_x in CO activation and conversion to hydrocarbons on the transition metal catalysts

Generally, in the Fischer Tropsch synthesis experiments, the pivotal intermediate CH_x(x = 1–3) are only regarded as the reactive species to participate into the reaction, and the other functions of CH_x(x = 1–3) species are ignored. The experiment hardly identifies the microscopic function mechanism of CH_x(x = 1–3) formed over the Co-based catalysts due to the dynamic change of CH_x(x = 1–3) intermediate. Through DFT calculations and microkinetic modeling, this work illustrates the new mechanism of CH_x(x = 1–3) adsorbed over Co catalyst (CH_x(x = 1–3)/Co) to catalyze syngas-to-hydrocarbon for the first time. The produced CH_x not only participates into the reactions as the reactive intermediate, but also performs the role of surface promoter to enhance the activity and selectivity toward CH_x(x = 1–3) and C₂ hydrocarbons. CH as the main monomer has the best promotion effect. Interestingly, the same things also occur in CO methanation over CH_x(x = 1–3)/Ni catalysts, which is highly active and selective toward methane. Thus, the new mechanism of CH_x(x = 1–3) intermediate as the catalytic assist located over the transition metal may be popularized in the other reaction systems.