The dehydrocyclization of naphtha is a process of great significance in the petrochemical industry, as it enables the production of valuable aromatics. While experimental studies have demonstrated the catalytic activity of H-ZSM-5 zeolite in converting alkanes to aromatics, there is a notable absence of theoretical investigations into the reaction mechanisms involved in the dehydrocyclization of naphtha. Herein, the conversion of n-heptane to toluene over H-ZSM-5 zeolite was examined using first-principles density functional theory (DFT) calculations. The dehydrocyclization process of n-heptane involves several key steps, including dehydrogenation, isomerization, and cyclization. Specifically, the dehydrogenation of n-heptane produces 1-heptene, 2-heptene, and 3-heptene, which then undergo various dehydrocyclization pathways leading to the formation of toluene: (i) C1-C5 ring closure of 1-heptene; (ii) C1-C6 ring closure of 1-heptene; (iii) C2-C6 ring closure of 2-heptene; (iv) dehydrogenation of 3-heptene to heptadiene, with C1-C5 ring closure; and (v) dehydrogenation of 3-heptene to heptatriene, with C1-C6 ring closure, followed by sequential ring expansion and/or dehydrogenation to toluene. The DFT results indicate that the dehydrogenation steps are energetically demanding, with the conversion of n-heptane to toluene via 1-heptene identified as the most favorable cyclization route. This theoretical investigation provides valuable insights into the fundamental mechanisms underlying the dehydrocyclization of naphtha for the production of aromatics, with potential implications for the development of more efficient catalytic processes in the petrochemical industry.

中文翻译：

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破译H-ZSM-5沸石正庚烷脱氢环化反应机理网络


石脑油脱氢环化在石化工业中是一个具有重要意义的过程，因为它可以生产有价值的芳烃。虽然实验研究已经证明了 H-ZSM-5 沸石在将烷烃转化为芳烃方面具有催化活性，但对石脑油脱氢环化反应机理的理论研究却明显缺乏。在此，使用第一原理密度泛函理论 (DFT) 计算检查了 H-ZSM-5 沸石上正庚烷向甲苯的转化。正庚烷脱氢环化过程涉及几个关键步骤，包括脱氢、异构化和环化。具体来说，正庚烷脱氢产生1-庚烯、2-庚烯和3-庚烯，然后它们经历各种脱氢环化途径，形成甲苯： (i) 1-庚烯的C1-C5闭环； (ii) 1-庚烯的C1-C6闭环； (iii) 2-庚烯的C2-C6闭环； (iv) 3-庚烯脱氢为庚二烯，C1-C5闭环； (v) 3-庚烯脱氢为庚三烯，C1-C6闭环，随后连续扩环和/或脱氢为甲苯。 DFT 结果表明，脱氢步骤需要大量能量，其中通过 1-庚烯将正庚烷转化为甲苯被认为是最有利的环化路线。这项理论研究为石脑油脱氢环化生产芳烃的基本机制提供了宝贵的见解，对石化工业中更有效的催化工艺的开发具有潜在影响。