The influence of inert cyclic reaction pathway on the Fischer-Tropsch mechanism based on the expanded FTS reaction network on χ-Fe5C2(510)

• The construction of an extended FTS reaction network for C 1 C 2 species based on the bond formation/dissociation principles between C/H/O atom. • The elementary reactions involving C 1 H a C 2 H b OH species omitted before are analyzed via DFT and found that the CO activation through them is accessible. • The CO activation through C 1 H a C 2 H b OH species is an inert cyclic reaction pathway and would compete with the major CO activation pathway, thereby reducing the TOF of CO activation pathway. • The concept of reaction frequency flow is proposed to find other inert cyclic reaction pathways and identify additional two. • The inert cyclic reaction pathways with low effective barrier energy would inhibit the FTS reaction activity by utilizing a significant number of active sites. Most theoretical simulation studies on the Fischer-Tropsch synthesis (FTS) reaction mechanism focus on only a portion of the FTS reaction network to obtain specific mechanistic insights, which often overlooks key mechanistic information in unconsidered network segments. Based on the concept of bonding and breaking chemical bonds, this work constructed an extended FTS reaction network encompassing C 1 to C 2 species on χ-Fe 5 C 2 (510) and it was found that the activation of CO, as a key rate limiting step in the formation of hydrocarbon products, may be achieved through the cleavage of C OH bonds, which is also an easily overlooked point in research. Micro kinetic analysis shows that the intermediate species C 1 C 2 HO in the main CO activation pathway can be hydrogenated to form C 1 C 2 HOH and C 1 HC 2 HOH first, then be dehydrogenated back to the C 1 HC 2 OH and C 1 C 2 HO, which will guide the formation of inert cyclic reaction pathway who would compete the main CO activation pathway on the adsorption sites, thereby reducing the TOF of the CO activation pathway. Though the inert cyclic reaction pathways is universality in the Fischer-Tropsch catalyst, we introduced the concept of "reaction frequency flow" to point out almost all the inert cyclic reaction pathways on χ-Fe 5 C 2 (510) by identifying active sites with reaction frequency flow. While most theoretical works attribute the limitation of reaction rates primarily to the high barrier energy of the rate-controlling step, this work highlights another mechanism that the inert cyclic reaction pathways could utilize a significant number of active sites, which would inhibit the FTS reaction activity.