Exploring coverage-dependent chain-growth mechanisms on Ru(111) for Fischer–Tropsch synthesis

Abstract

The chain growth mechanisms of Fischer–Tropsch synthesis (FTS) remain a controversial topic, especially considering the much stronger adsorption ability of CO over H₂, resulting in CO pre-adsorption or saturation. Systematic periodic density functional theory computations (GGA-rPBE), and the analysis of ab initio atomistic thermodynamics and micro-kinetics on the Ru(111) surface revealed that the dense CO layer at a very early stage of FTS suppresses CO activation, promotes the coupling of CH_x (x = 0–3) and C1 as an insertion monomer (C1 = C, CH, CH₂, CH₃, CO, HCO and COH) under favorable conditions, especially for CH₂ (or CH₃) + CO coupling mechanisms. An HCO-insertion mechanism into RCH (R = H, CH₃, …) [HCO + CH₂ → CH₂CHO → CH₂CO → CH₃CO → CH₃C + O → CH₃CH (+ HCO) → …] was proposed at the lowest coverage, while a CO insertion mechanism into RCH (R = H, CH₃, …) [CO + CH₂ → CH₂CO (CH₃ + CO) → CH₂C + O (CH₃CO) → CH₃C + O → CH₃CH (+ CO) → …] was proposed at CO pre-saturation coverage (423 K, 10 atm) on the Ru(111) surface.