Ga/ZSM-5 is widely used to catalyze propane dehydrogenation (PDH). For the harsh operation conditions, the detailed active species, and the plausible reaction pathways that are responsible for the observed superior PDH performance remain unresolved for Ga/ZSM-5. Reduced extraframework Ga hydride species trapped at zeolite framework Al-pairs, including b[GaH]2+, [Ga]+-BAS, [GaH2]+-BAS, etc. are an important kind of Ga species known as active species for PDH. In this work, the PDH pathways these over these Ga species were investigated theoretically at temperatures and pressures relevant to experiments. We showed that dynamically generated undercoordinated b[GaH]2+ would exhibit significantly higher catalytic activity at PDH conditions as compared with other Ga hydride species. The most plausible PDH pathway over b[GaH]2+ is the carbenium pathway. The Ga species and BAS act in concert in promoting the H2 elimination and β-H transfer, and in turning PDH efficient. Ga hydride species may also form as intermediates along the PDH pathways as active sites for subsequent activation and conversion of propane, suggesting the evolution of Ga hydride species trapped by Al-pairs in Ga/ZSM-5 at operation conditions. The findings are expected to pave the way for better understanding of the experimentally observed operation condition dependent PDH performance of Ga/ZSM-5.

中文翻译：

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MFI 分子筛中 Al-对物处捕获的框架外 Ga 氢化物物种丙烷脱氢的理论研究


Ga/ZSM-5 广泛用于催化丙烷脱氢 （PDH）。对于恶劣的操作条件，详细的活性物质和导致 Ga/ZSM-5 观察到的卓越 PDH 性能的合理反应途径仍未解决。被困在沸石框架 Al-对上的还原框架外 Ga 氢化物物质，包括 b[GaH]2+、[Ga]+-BAS、[GaH2]+-BAS 等，是一种重要的 Ga 物质，被称为 PDH 的活性物质。在这项工作中，在与实验相关的温度和压力下，从理论上研究了这些 Ga 物种上的 PDH 途径。我们发现，与其他 Ga 氢化物物种相比，动态生成的配位不足的 b[GaH] 2+ 在 PDH 条件下将表现出显着更高的催化活性。b[GaH]2+ 上最合理的 PDH 通路是碳鎓通路。Ga 物种和 BAS 协同作用，促进 H2 消除和 β-H 转移，并提高 PDH 的效率。Ga 氢化物物质也可能作为 PDH 途径的中间体形成，作为随后丙烷活化和转化的活性位点，这表明在操作条件下被 Ga/ZSM-5 中的 Al-对捕获的 Ga 氢化物物质的进化。这些发现有望为更好地理解实验观察到的 Ga/ZSM-5 依赖于运行条件的 PDH 性能铺平道路。