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Insight into the Formation of CO X By‐Products in Methanol‐to‐Aromatics Reaction over Zn/HZSM‐5: Significantly Affected by the Chemical State of Surface Zn Species
Author(s) -
Li Junhui,
Gong Qing,
Liu Yifei,
Kang Rongrong,
Yang Chengguang,
Qiu Minghuang,
Hu Zhonghua,
Zhu Zhirong
Publication year - 2019
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201901226
Subject(s) - dehydrogenation , catalysis , chemistry , methanol , selectivity , aromatization , inorganic chemistry , steam reforming , metal , zinc , decomposition , photochemistry , organic chemistry , hydrogen production
Several Zn‐modified HZSM‐5 catalysts prepared by impregnation or ion exchange were characterized, and tested in methanol‐to‐aromatics (MTA) reaction. The obviously enhanced output of CO X by‐products (CO & CO 2 ) was observed over these modified catalysts, although they showed the significantly improved selectivity of aromatics. It was found CO X formation is actually determined by the chemical state of surface Zn species. Concretely, both surface ZnO and surface metal‐zinc are the reactive sites for the conversion of methanol to CO X and H 2 . At the initial period of reaction, surface ZnO (no reduction) causes CO X (mainly CO 2 ) formation may almost‐exclusively through methanol steam‐reforming. With the extending of reaction‐time, while it′s partially reduced to metal‐zinc which more violently catalyzes the conversion of methanol to CO X (both CO and CO 2 ) may through the pathway of first dehydrogenation‐decomposition and subsequent Water‐Gas‐Shift reaction. However, the surface ZnOH + species as Lewis acid hardly results in CO X formation, but significantly promotes aromatization due to its interaction‐dehydrogenation effect. As high as possible ratio of the ZnOH + in surface Zn species is conducive to both suppressing the side‐reaction which produces CO X and incubating the high aromatic selectivity even in the time‐on‐stream reaction. Our work may provide a theoretical guidance for developing the elegant catalyst for the MTA process with high carbon atom utilization.