Mesoporous HZSM-5 Supported Zn Catalyst for Improved Ethane Aromatization
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Mesoporous HZSM‑5 Supported Zn Catalyst for Improved Ethane Aromatization Xia Xu1,2 · Yan Zhang1 · Xuefa Xia1,2 · Fangyi Liang1 · Heqing Jiang1 Received: 18 November 2019 / Accepted: 1 May 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Ethane aromatization is a promising process to achieve the efficient utilization of abundant ethane into high value-added chemicals. However, rapid coking deactivation has hindered the application of this technique. In this work, to improve catalyst stability, mesopores are introduced into the conventional Zn modified HZSM-5 catalysts. ICP, XRD, N2 adsorption–desorption, HRTEM, NH3-TPD, TG, and XPS are used to study the structure property, acidity, and coke formation of conventional and mesoporous catalysts. For ethane aromatization, upon reacting for 262 min, the yield of main products including benzene, toluene, and ethylene decreased by 48.7% for conv-Zn/HZSM-5 while only 16.6% for meso-Zn/HZSM5. The significantly enhanced catalytic activity and stability of meso-Zn/HZSM-5 is primarily ascribed to the generation of mesopores after alkali treatment. As suggested by TG and N 2 adsorption–desorption, conv-Zn/HZSM-5 exhibited not only faster coke deposition than meso-Zn/HZSM-5, but also major coke formation within the micropores, thus accelerating the catalyst deactivation. In contrast, the introduction of mesopores seems to availably facilitate the diffusion and escape of products from zeolite channels and subsequently suppress the internal coke formation, resulting in improved catalyst stability. In addition, a reaction-regeneration protocol was operated on meso-Zn/HZSM-5, which can effectively remove the deposited coke and extend the life of catalyst. Graphic Abstract
Keywords Mesoporous · HZSM-5 · Ethane aromatization · Coke · Regeneration
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03246-4) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
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1 Introduction Benzene, toluene, and xylenes obtained by aromatization of light alkanes with modified ZSM-5 catalysts have attracted great attention. However, rapid coking deactivation has hindered the application of this technique. Generally, carbon deposition includes internal coke and external coke, among which internal coke is considered as the main cause of catalyst deactivation because internal coke can cover the active acid sites and block the micropores [1]. For conventional zeolite, the presence of micropores restricts the diffusion of reactant and product molecules, and simultaneously limits the removal of coke precursors from zeolite channels, thus accelerating the formation of internal coke. To overcome this problem, nanosized zeolites [2–5], zeolite nanosheets [1, 6–9], and mesoporous zeolites [10–14] have been designed to shorten the diffusion path and improve mass transfer. Especially, the introduction o
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