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Isomorphously Substituted [Fe,Al]ZSM-5 Catalysts for Methane Dehydroaromatization
ACS Catalysis ( IF 12.9 ) Pub Date : 2023-06-02 , DOI: 10.1021/acscatal.3c00854
Yujie Liu, Aleksei Bolshakov, Marita Ćoza, Victor Drozhzhin, Emiel J. M. Hensen, Nikolay Kosinov

Dehydroaromatization of methane (MDA) under non-oxidative conditions is a promising reaction for direct valorization of natural gas and biogas. Typically, Fe-modified ZSM-5 catalysts display low aromatic productivity and high coke selectivity in the MDA reaction. Herein, we show the benefit of starting from isomorphously substituted Fe-sites in [Fe,Al]ZSM-5 zeolites prepared by direct hydrothermal synthesis. Upon calcination, these samples contain predominantly isolated Fe3+ species, either atomically dispersed within the zeolite framework or anchored at exchange sites inside zeolite channels. In terms of the integral hydrocarbon productivity, [Fe,Al]ZSM-5 catalysts outperform Fe/ZSM-5, prepared by impregnation, as well as Mo/ZSM-5 catalysts with the same Si/Al ratio and molar metal loading. Operando X-ray absorption spectroscopy coupled with mass spectrometry (XANES-MS) demonstrates that the initial tetrahedral Fe3+ within the zeolite framework or at exchange sites are transformed into octahedral extraframework Fe2+ active sites during the MDA reaction and form small Fe2O3 clusters during oxidative regeneration. Combining activity measurements and operando thermogravimetry shows that the duration of the induction period, related to the formation of active hydrocarbon pool intermediates, strongly depends on the Fe dispersion and loading and can be used as a suitable descriptor for the MDA activity of [Fe,Al]ZSM-5. The shorter induction period of [Fe,Al]ZSM-5 in comparison to impregnated Fe/ZSM-5 can be linked to the higher methane conversion rate over highly dispersed Fe-sites and faster formation of active hydrocarbon pool intermediates.

中文翻译:

同晶取代 [Fe,Al]ZSM-5 甲烷脱氢芳构化催化剂

在非氧化条件下甲烷脱氢芳构化 (MDA) 是天然气和沼气直接增值的有前途的反应。通常,Fe 改性的 ZSM-5 催化剂在 MDA 反应中表现出低芳烃生产率和高焦炭选择性。在此,我们展示了从通过直接水热合成制备的 [Fe,Al]ZSM-5 沸石中同晶取代的 Fe 位点开始的好处。煅烧后,这些样品主要含有孤立的 Fe 3+物种,原子分散在沸石框架内或锚定在沸石通道内的交换位点。就整体烃类生产率而言,[Fe,Al]ZSM-5 催化剂优于通过浸渍法制备的 Fe/ZSM-5,以及具有相同 Si/Al 比和摩尔金属负载量的 Mo/ZSM-5 催化剂。Operando X 射线吸收光谱与质谱 (XANES-MS) 相结合表明,在 MDA 反应过程中,沸石骨架内或交换位点的初始四面体 Fe 3+转化为八面体骨架外 Fe 2+活性位点并形成小的 Fe 23氧化再生过程中的簇。结合活性测量和操作热重分析表明,与活性烃池中间体的形成相关的诱导期持续时间在很大程度上取决于 Fe 分散和负载,并且可以用作 [Fe,Al 的 MDA 活性的合适描述符]ZSM-5。与浸渍 Fe/ZSM-5 相比,[Fe,Al]ZSM-5 的诱导期更短可能与高度分散的 Fe 位点上甲烷转化率更高以及活性烃池中间体的形成更快有关。
更新日期:2023-06-02
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