The effect of cobalt promoter on the CO methanation reaction over MoS2 catalyst: a density functional study

The potential mechanism of sulfur-resistant CO methanation was theoretically investigated via density functional theory (DFT + D) calculations. Comparisons were made between modified Co–MoS2 and pure MoS2 catalysts and we highlighted the distinguished CO methanation pathway in the presence of Co-promoter. Multiple intermediates were formed at different catalytic sites during the reaction, which further increased the mechanism complexity. The results obtained from Co–MoS2 imply that the CH3OH species could be formed along the most feasible reaction pathway on Mo catalyst termination; the subsequent dissociation of CH3OH into CH3 and OH was found to be the rate determining step with a reaction barrier of 29.35 kcal mol−1 at 750 K. On the S edge of Co–MoS2, the CH2OH intermediate could be formed as a result of CH2O reacting with adsorbed hydrogen, and subsequent CH2OH dissociation was noted to release CH2. Afterwards, consecutive hydrogenation of CH2 led to the final CH4 yield. On S catalyst termination, it was suggested that the CHO intermediate formation played a key role as the rate-determining step with the reaction barrier of 19.56 kcal mol−1 at 750 K. By comparing the CO methanation energy profiles over different samples, it was discovered that the Co-promoter did possess promoting effects at both the Mo edge and the S edge of the catalyst; note that this enhancement at the Mo edge was superior to that at the S edge, especially for larger scale applications. Moreover, after doping with Co, the OH species was easier to remove in terms of H2O molecules, which created enough vacant active sites for a continuous reaction.