Mechanism of methanol synthesis on Ni(110)

Abstract

Planewave density functional theory (DFT-PW91) calculations are employed to study the methanol synthesis through CO₂ and CO hydrogenation, as well as the two side reactions: the water gas shift (WGS) reaction and formic acid formation, on Ni(110). For the WGS reaction on Ni(110), we find that the redox mechanism is favored over the carboxyl-mediated mechanism. We show that the formate pathway is the dominant one for formic acid formation. For methanol synthesis through CO₂ and CO hydrogenation on Ni(110), our results reveal that the formic-acid- and dioxymethylene-mediated pathways coexist, in contrast to methanol synthesis on Cu(111) where the formic-acid-mediated pathway dominates. We also find that on Ni(110), hydrogenation of CH₂O* to CH₃O* and that to CH₂OH* both contribute to MeOH synthesis. Based on the derived energetics, we ascertain that CH₃O* hydrogenation to CH₃OH* is likely the rate-determining step along the CH₃O* pathway on Ni(110). Remarkably, CH₃O* hydrogenation can be facilitated by the presence of HCO*, demonstrating the promotional effect of CO. We further show that CO also participates in methanol synthesis directly via its hydrogenation to HCO* and further to CH₂O*. Additional microkinetic modeling by considering feed composition and reaction conditions would provide further mechanistic insights into methanol synthesis on Ni(110).