Ga/ZSM-5 is highly efficient for the direct dehydrogenation of propane (PDH) and binuclear Ga-oxo species were recently proposed to account for the observed PDH performance. However, it is still challenging to determine the active sites and reaction mechanisms at the harsh operation conditions. In this work, the thermodynamic stability and PDH mechanisms of binuclear Ga-oxo species stabilized by paired Al- sites in Ga/ZSM-5, including [GaO], [GaOH], [HGaOGaOH], [GaOGa], [Ga]-[Ga(OH)], etc. were investigated with extensive first-principles based calculations. [Ga] not only exists stably when isolated but also interacts with neighboring oxidized Ga species to stabilize them. This enhanced stability can be attributed to the change of Ga coordination and formation of Ga-O-Ga bridge. The most plausible PDH mechanisms over these Ga-oxo species are all alkyl mechanisms. The calculated free energy barriers for PDH steps can all be correlated with the thermodynamic stability of the Ga-oxo species. Further to these, [HGaOGaOH] would exhibit superior performance in PDH for the fine balance between the thermodynamics stability and activity. Intermediate Ga-oxo species with better thermostability may form during PDH over these Ga-oxo species, making the regeneration of the active sites demanding. However, some of these intermediate Ga-oxo species are also eligible as active sites for PDH, such as [HGaOGaOH]. We expect the findings would help to rational the knowledge on PDH over Ga-oxo species, as well as the operation condition driven evolution of reaction sites for catalysis in harsh conditions and pave the way for design and fabrication of Ga-based catalysts of superior performance for conversion of light alkanes.

中文翻译：

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Ga/ZSM-5 中配对 Al 位点稳定的双核 Ga-氧物种上的丙烷脱氢：第一性原理研究


Ga/ZSM-5 对于丙烷直接脱氢 (PDH) 非常有效，最近提出了双核 Ga-oxo 物种来解释观察到的 PDH 性能。然而，确定恶劣操作条件下的活性位点和反应机制仍然具有挑战性。在这项工作中，Ga/ZSM-5 中成对 Al-位点稳定的双核 Ga-氧物种的热力学稳定性和 PDH 机制，包括 [GaO]、[GaOH]、[HGaOGaOH]、[GaOGa]、[Ga]- [Ga(OH)]等通过基于第一原理的广泛计算进行了研究。 [Ga]不仅在孤立时稳定存在，而且还与邻近的氧化Ga物种相互作用以稳定它们。这种稳定性的增强可归因于Ga配位的变化和Ga-O-Ga桥的形成。这些 Ga-氧物种中最合理的 PDH 机制都是烷基机制。计算出的 PDH 步骤的自由能垒都可以与 Ga-oxo 物质的热力学稳定性相关。除此之外，[HGaOGaOH] 在 PDH 中表现出优异的性能，实现热力学稳定性和活性之间的良好平衡。在 PDH 过程中，可能会在这些 Ga-oxo 物质上形成具有更好热稳定性的中间 Ga-oxo 物质，从而对活性位点的再生提出要求。然而，其中一些中间 Ga-氧物种也适合作为 PDH 的活性位点，例如 [HGaOGaOH]。我们希望这些发现将有助于理顺对 Ga-oxo 物种的 PDH 的了解，以及操作条件驱动的恶劣条件下催化反应位点的演变，并为设计和制造高性能的 Ga 基催化剂铺平道路用于轻质烷烃的转化。