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Local structure elucidation and reaction mechanism of light naphtha aromatization over Ga embedded H-ZSM-5 zeolite: Combined DFT and experimental study
Microporous and Mesoporous Materials ( IF 5.2 ) Pub Date : 2020-07-02 , DOI: 10.1016/j.micromeso.2020.110414
Yutthana Wongnongwa , Pinit Kidkhunthod , Usa Sukkha , Sitthiphong Pengpanich , Kaew-arpha Thavornprasert , Jakkrapong Phupanit , Nawee Kungwan , Gang Feng , Tinnagon Keawin , Siriporn Jungsuttiwong

Local structures and mechanisms for n-pentane aromatization on Ga embedded H-ZSM-5 zeolite (Ga/ZSM-5) were elucidated using Synchrotron-based X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations to understand the role of Ga/ZSM-5 zeolite in aromatics synthesis. XAS data suggests that Ga ligates with four oxygen or four hydrogen atoms. Catalytic tests results suggest that conversion by Ga/ZSM-5 catalyst cannot occur via C6–C8 non-aromatic intermediates, while the availability of Ga metal sites promotes the aromatization of C2 and C3 species. Therefore, conversion of n-pentane to benzene or toluene comprises four steps, i) cracking, ii) GaH2 activation, iii) cyclization, and iv) dehydrogenation. Our model predicts the key intermediate in n-pentane aromatization on Ga/ZSM-5 zeolite to be a five-membered Ga-C4 ring structure. The ring undergoes expansion to form a seven-membered Ga-C6 ring. Moreover, we discuss thermodynamics and kinetic results for the benzene and toluene formation pathways. Our results provide new finding for the role of Ga/ZSM-5 zeolites in n-pentane aromatization processes.



中文翻译:

Ga嵌入的H-ZSM-5分子筛上轻石脑油芳构化的局部结构解析和反应机理:DFT与实验研究相结合

使用基于同步加速器的X射线吸收光谱(XAS)和密度泛函理论(DFT)计算来阐明Ga嵌入的H-ZSM-5沸石(Ga / ZSM-5)上戊烷芳构化的局部结构和机理。Ga / ZSM-5沸石在芳烃合成中的作用 XAS数据表明Ga与四个氧或四个氢原子连接。催化测试结果表明,Ga / ZSM-5催化剂不能通过C6-C8非芳族中间体发生转化,而Ga金属位点的可用性促进了C2和C3物种的芳构化。因此,戊烷向苯或甲苯的转化包括四个步骤,i)裂解,ii)GaH 2活化,iii)环化和iv)脱氢。我们的模型预测,Ga / ZSM-5沸石在戊烷芳构化中的关键中间体为五元Ga-C4环结构。该环经历膨胀以形成七元Ga-C6环。此外,我们讨论了苯和甲苯形成途径的热力学和动力学结果。我们的结果为Ga / ZSM-5沸石在戊烷芳构化过程中的作用提供了新发现。

更新日期:2020-07-15
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