Elementary steps of syngas reactions on Mo₂C(0 0 1): Adsorption thermochemistry and bond dissociation

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• 作者：Andrew J. Medford^a ; ^b ; Aleksandra Vojvodic^a ; ^b ; ^{alevoj@slac.stanford.edu} ; Felix Studt^b ; Frank Abild-Pedersen^b ; Jens K. Nø ; rskov^a ; ^b
• 关键词：Molybdenum carbide ; Synthesis gas conversion ; Density functional theory ; Brø ; nsted&ndash ; Evans&ndash ; Polanyi relationships ; Adsorption energy scaling ; Surface composition ; Surface termination
• 刊名：Journal of Catalysis
• 出版年：2012
• 期刊代码：97_00219517
• 类别：ce
• 出版时间：June, 2012
• 卷：290
• 期：Complete
• 页码：108-117
• 文件大小：1522 K

摘要

Density functional theory (DFT) and ab initio thermodynamics are applied in order to investigate the most stable surface and subsurface terminations of Mo₂C(0 0 1) as a function of chemical potential and in the presence of syngas. The Mo-terminated (0 0 1) surface is then used as a model surface to evaluate the thermochemistry and energetic barriers for key elementary steps in syngas reactions. Adsorption energy scaling relations and Br酶nsted-Evans-Polanyi relationships are established and used to place Mo₂C into the context of transition metal surfaces. The results indicate that the surface termination is a complex function of reaction conditions and kinetics. It is predicted that the surface will be covered by either C₂H₂ or O depending on conditions. Comparisons with transition metals indicate that the Mo-terminated Mo₂C(0 0 1) surface exhibits carbon reactivity similar to transition metals such as Ru and Ir, but is significantly more reactive toward oxygen. This explains some previous observations for Mo₂C catalysts and suggests that Mo₂C may exhibit unique and potentially useful reactivity or selectivity patterns.