A first-principles study of CO hydrogenation into methane on molybdenum carbides catalysts

• Published in: Surface science 2013-08, Vol.614, p.53-63
• Main Authors: Qi, Ke-Zhen, Wang, Gui-Chang, Zheng, Wen-Jun
• Format: Article
• Language: English
• Subjects: Carbon monoxide; Catalysis; Close packed lattices; CO hydrogenation; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Density functional calculations; Exact sciences and technology; Hexagonal cells; Hydrogenation; Mathematical models; Methane; Molybdenum carbide; Physics; Reaction mechanisms; Surface chemistry
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2013.04.001

The reaction mechanisms for the CO hydrogenation to produce CH4 on both fcc-Mo2C (100) and hcp-Mo2C (101) surfaces are investigated using density functional theory calculations with the periodic slab model. Through systematic calculations for the mechanisms of the CO hydrogenation on the two surfaces, we found that the reaction mechanisms are the same on both fcc and hcp Mo2C catalysts, that is, CO→HCO→H2CO→H2COH→CH2→CH3→CH4. The activation energy of the rate-determining step (CH3+H→CH4) on fcc-Mo2C (100) (0.84eV) is lower than that on hcp-Mo2C (101) (1.20eV), and that is why catalytic activity of fcc-Mo2C is higher than hcp-Mo2C for CO hydrogenation. Our calculated results are consistent with the experimental observations. The activity difference of these two surfaces mainly comes from the co-adsorption energy difference between initial state (IS) and transition state (TS), that is, the co-adsorption energy difference between IS and TS is −0.04eV on fcc Mo2C (100), while it is as high as 0.68eV on hcp Mo2C (101), and thus leading to the lower activation barrier for the reaction of CH3+H→CH4 on fcc-Mo2C (100) compared to that of hcp-Mo2C (101). [Display omitted] •DFT calculations were performed to study CO hydrogenation to methane on Mo2C.•Reaction mechanism is CO→HCO→H2CO→H2COH→CH2→CH3→CH4 on Mo2C.•CH3+H→CH4 is the rate-determining step.•Barrier of CH3+H→CH4 on fcc-Mo2C (100) is lower than on hcp-Mo2C (101).