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Acetylene and Ethylene Adsorption on a β-Mo2C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Jimenez-Orozco, Carlos, Florez, Elizabeth, Moreno, Andres, Liu, Ping, Rodriguez, José A.
The Journal of Physical Chemistry C 2017 v.121 no.36 pp. 19786-19795
adsorption, alkynes, catalysts, catalytic activity, ethylene, geometry, hydrogenation, methodology, molybdenum
Mo₂C catalysts are widely used in hydrogenation reactions; however, the role of the C and Mo terminations in these catalysts is not clear. Understanding the binding of adsorbates is key for explaining the activity of Mo₂C. The adsorption of acetylene and ethylene, probe molecules representing alkynes and olefins, respectively, was studied on a β-Mo₂C(100) surface with C and Mo terminations using calculations based on periodic density functional theory. Moreover, the role of the C/Mo molar ratio was investigated to compare the catalytic potential of cubic (δ-MoC) and orthorhombic (β-Mo₂C) surfaces. The geometry and electronic properties of the clean δ-MoC(001) and β-Mo₂C(100) surfaces have a strong influence on the binding of unsaturated hydrocarbons. The adsorption of ethylene is weaker than that of acetylene on the surfaces of the cubic and orthorhombic systems; adsorption of the hydrocarbons was stronger on β-Mo₂C(100) than on δ-MoC(001). The C termination in β-Mo₂C(100) actively participates in both acetylene and ethylene adsorption and is not merely a spectator. The results of this work suggest that the β-Mo₂C(100)-C surface could be the one responsible for the catalytic activity during the hydrogenation of unsaturated CC and CC bonds, while the Mo-terminated surface could be poisoned or transformed by the strong adsorption of C and CHₓ fragments.