M1 phase MoVTeNb mixed oxides exhibit unique catalytic properties that lead to high C₂H₄ yields in oxidative conversion of C₂H₆ at moderate temperatures. The role of the heptagonal channel micropores of the M1 phase in regulating reactivity and selectivity is assessed here using reactant size-dependent kinetic probes and density functional theory (DFT) treatments for C₂H₆ and cyclohexane (C₆H₁₂) activations inside and outside the micropores. The sizes of C₂H₆ and the micropores suggest a tight guest–host fit, but C₆H₁₂ cannot access intrapore sites. Measured C₂H₆ to C₆H₁₂ activation rate ratios on MoVTeNbO are much higher than those measured on nonmicroporous vanadium oxides (VO_x/SiO₂) and estimated by DFT on external surfaces, suggesting that most C₂H₆ activations on MoVTeNbO occur inside the micropores under typical conditions. C₂H₆ exhibits higher activation energy than C₆H₁₂ on VO_x/SiO₂, consistent with the corresponding C–H bond strengths; the activation energy difference between C₂H₆ and C₆H₁₂ is lower on MoVTeNbO because micropores stabilize C–H activation transition states through van der Waals interactions. Product selectivities for C₂H₆ and C₆H₁₂ suggest that the ability of VO_x/SiO₂ to activate C–H bonds and resist O-insertion in products is similar to the external surfaces of MoVTeNbO, but the micropores in the latter oxides are more selective for C–H activation. DFT calculations show that the tight confinement in micropores hinders the C–O contact necessary for O-insertion. These insights provide guidance for utilizing shapes and sizes of confining voids to mitigate selectivity limitations dictated by thermodynamics of sequential oxidation reactions and electronic properties of redox catalysts.

中文翻译：

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密闭性对乙烷在MoVTeNb混合氧化物上的选择性氧化脱氢的影响

M1相MoVTeNb混合氧化物表现出独特的催化性能，在中等温度下C ₂ H _6的氧化转化可导致高C ₂ H ₄收率。M1相的七边形通道微孔在调节反应性和选择性中的作用，使用反应物尺寸依赖性动力学探针和密度泛函理论（DFT）处理，对内部和外部的C ₂ H ₆和环己烷（C ₆ H ₁₂）活化进行了评估。在微孔之外。C ₂ H ₆的大小和微孔表明紧密的客体-宿主配合，但C ₆ H ₁₂无法访问孔内站点。在MoVTeNbO上测得的C ₂ H ₆与C ₆ H ₁₂活化速率比远高于在无微孔氧化钒（VO _x / SiO ₂）上测定并通过DFT在外表面上估计的比率，这表明在MoVTeNbO上大多数C ₂ H ₆活化在典型条件下发生在微孔内部。C ₂ H ₆在VO _x / SiO ₂上的活化能比C ₆ H _12高，这与相应的C–H键强度一致。C之间的活化能差MoVTeNbO上的₂ H ₆和C ₆ H ₁₂较低，因为微孔通过范德华相互作用稳定了C–H活化转变状态。对C ₂ H ₆和C ₆ H _12的产物选择性表明VO _x / SiO ₂的能力激活C–H键并抵抗产品中的O插入的作用类似于MoVTeNbO的外表面，但后者氧化物中的微孔对C–H激活的选择性更高。DFT计算表明，微孔中的紧密限制阻碍了O插入所需的C–O接触。这些见解提供了利用限制空隙的形状和大小来减轻由顺序氧化反应的热力学和氧化还原催化剂的电子性质所决定的选择性限制的指南。