The first (oxidative) dehydrogenation step of light alkanes (ethane, propane, and n-butane) on transition-metal (closed-packed and stepped) surfaces is analyzed using density functional theory (DFT) calculations. It is shown that the transition-state energies (ΔE_TS) of the C–H bond activation scale linearly with the corresponding final-state energies (ΔE_FS), and all alkanes studied here share the same linear scaling relationships for the nonoxidative, oxygen-assisted, and hydroxyl-assisted reactions. Variations in ΔE_TS between alkanes can be mainly attributed to differences in dispersion contributions determined by the carbon-chain length. As the carbon chain increases, the ΔE_TS of the alkane C–H bond activation decreases. In addition, the ΔE_TS of the first (O)DH step of propane and n-butane is linearly correlated with the ΔE_TS of the first ethane (O)DH step. We also find that the oxygen and hydroxyl adsorption energies on the transition-metal surfaces (closed-packed and stepped) are dictating the promoting/poisoning effect of the C–H bond activation. Based on our extensive DFT calculations, we find that Pt has the lowest C–H bond transition-state energy for both the nonoxidative and oxidative pathways, and metals such as Au and Ag become active for C–H bond activation of alkanes only when oxygen and hydroxyl species are present on the metal surfaces. Finally, by establishing scaling relationships over a wide range of transition-metal surfaces, we have developed a simple and highly accurate model for the prediction of C–H bond activation barriers for the (oxidative) dehydrogenation of light alkanes.

中文翻译：

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过渡金属表面上轻烷烃活化的趋势

使用密度泛函理论（DFT）计算分析了过渡金属（密堆积和阶梯状）表面上的轻质烷烃（乙烷，丙烷和正丁烷）的第一步（氧化）脱氢步骤。结果表明，C–H键活化的过渡态能量（ΔE _TS）与相应的最终态能量（ΔE _FS）呈线性比例关系，此处研究的所有烷烃对于非氧化性均具有相同的线性比例关系，氧气辅助和羟基辅助反应。烷烃之间的ΔE _TS的变化可主要归因于由碳链长度决定的分散贡献的差异。随着碳链的增加，ΔE烷烃CH键活化的_TS降低。此外，Δ Ë _TS第一（O）DH丙烷的步骤和Ñ丁烷线性与Δ相关È _TS第一乙烷（O）DH步骤的步骤。我们还发现过渡金属表面（密排和阶梯状）上的氧和羟基吸附能决定了C–H键活化的促进/中毒作用。根据我们广泛的DFT计算，我们发现Pt在非氧化和氧化途径中均具有最低的C–H键过渡态能，并且只有当氧存在时，Au和Ag等金属才对烷烃的C–H键活化有活性。金属表面上存在羟基和羟基。最后，通过在各种过渡金属表面上建立标度关系，我们开发了一种简单且高度准确的模型，用于预测轻烷烃（氧化）脱氢的C–H键活化势垒。