Insight into the mechanism of methane synthesis from syngas on a Ni(111) surface: a theoretical study

Abstract

The mechanism of methane synthesis from syngas on a Ni(111) surface has been systematically investigated using the density functional theory method together with the periodic slab model, which covers the main existence form of CH_x (x = 1–3) species and all possible formation pathways. Our results show that CO hydrogenation to a HCO intermediate is more favorable than CO desorption and CO direct dissociation on Ni(111); starting from HCO, six possible formation pathways of CH_x (x = 1–3) species are considered: (i) HCO → CH, (ii) HCO → HCOH → CH, (iii) HCO → HCOH → CH₂OH → CH₂, (iv) HCO → CH₂O → CH₂, (v) HCO → CH₂O → CH₂OH → CH₂, (vi) HCO → CH₂O → CH₃O → CH₃, followed by CH_x (x = 1–3) successive hydrogenation to CH₄, suggesting that CH is the dominate existing form of CH_x (x = 1–3) species involving in CH₄ formation from syngas, which is dominantly formed by two parallel reaction pathways (i) and (ii), followed by the sequential hydrogenation of CH species to CH₄. Meanwhile, surface C is mainly formed by the pathway of CO → HCO (HCOH) → CH → C. Furthermore, beginning with the key CH intermediate, CH preferred to be hydrogenated to CH₂ rather than being dissociated into C.