The viability of alkane oxidative dehydrogenation (ODH) processes specifically, and catalytic partial oxidation reactions more generally, are oftentimes limited by the formation of undesired deep oxidation products such as CO and CO₂. The forced dynamic operation (FDO) of catalytic reactors has been proposed as a means for enhancing desired olefin or oxygenate selectivity and yield over those of CO and CO₂, but an elucidation of the precise mechanistic bases for the dynamic enhancement observed continues to remain evasive. In this work, we provide an explanation of the extent of dynamic enhancement noted during ethane ODH over supported MoO_x catalysts but not VO_x ones─an explanation grounded in a quantitative analysis of the density and reactivity of chemisorbed and lattice oxygen species on these two classes of catalysts. Supported vanadia catalysts, unlike molybdena ones, carry oxygen species with similar reducibilities, resulting in highly contrasting trends in dynamic and steady state ODH properties for the two catalysts. Whereas in the case of VO_x/Al₂O₃, oxygen speciation affects the nature of the hydrocarbon activated (ethane or ethylene), in the case of MoO_x/Al₂O₃, it affects the type of product formed (ethylene or CO_x). Metal oxide loading is shown to be a key parameter impacting dynamic enhancement, with the FDO enhancement of higher loading molybdena samples converging toward that of the vanadia catalyst. The preferential depletion of chemisorbed oxygens is revealed to be a key determinant of the extent of dynamic enhancement, with an asymmetry in modeled O_*/O_L ratios under dynamic conditions relative to SS ones helping rationalize the effect that modulation frequency has on FDO enhancement. Collectively, the results presented here establish a quantitative, molecular-level basis for dynamic enhancement noted during the ODH of ethane, and point to considerations relating to the reactivity of chemisorbed and lattice oxygens as well as their dynamic and steady state ratios as levers for mitigating side-product formation through FDO.

中文翻译：

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乙烷氧化脱氢强制动态操作过程中提高选择性的动力学要求

具体来说，烷烃氧化脱氢(ODH)过程以及更一般的催化部分氧化反应的可行性常常受到不需要的深度氧化产物(例如CO和CO _{2 )}的形成的限制。催化反应器的强制动态操作（FDO）已被提议作为提高所需烯烃或含氧化合物选择性和产率（相对于CO和CO ₂的选择性和产率）的手段，但对所观察到的动态增强的精确机械基础的阐明仍然是回避的。 。在这项工作中，我们解释了乙烷 ODH 在负载型 MoO _x催化剂而非 VO _x催化剂上的动态增强程度，这一解释基于对这两种催化剂上化学吸附和晶格氧物种的密度和反应性的定量分析催化剂类别。与钼催化剂不同，负载型氧化钒催化剂携带具有相似还原性的氧物质，导致两种催化剂的动态和稳态 ODH 性质呈现出截然不同的趋势。而在 VO _x /Al ₂ O ₃的情况下，氧形态会影响活化烃（乙烷或乙烯）的性质，而在 MoO _x /Al ₂ O ₃的情况下，它会影响形成的产物类型（乙烯或乙烯）。二氧化碳_）。金属氧化物负载量被证明是影响动态增强的关键参数，较高负载量的钼样品的 FDO 增强趋向于氧化钒催化剂的增强。研究表明，化学吸附氧的优先耗尽是动态增强程度的关键决定因素，动态条件下模拟的 O _* /O _L比率相对于 SS 比率的不对称性有助于合理化调制频率对 FDO 增强的影响。总的来说，这里提出的结果为乙烷 ODH 过程中注意到的动态增强建立了定量的分子水平基础，并指出了与化学吸附氧和晶格氧的反应性以及它们的动态和稳态比率作为缓解杠杆的考虑因素通过 FDO 形成副产物。