Evolution of Zn Species on Zn/HZSM‐5 Catalyst under H₂ Pretreated and its Effect on Ethylene Aromatization

Abstract

Aromatization reaction is of importance in producing aromatics, accompanied by the generation of abundant H2, which may influence the reaction by interacting with the catalyst. In this work, Zn‐containing ZSM‐5 prepared by impregnation was treated in H2 atmosphere at different temperatures, and the evolution in structure, acidity, and Zn species distribution were studied. The catalyst's performance in ethylene aromatization was also evaluated. The results show that the H2 atmosphere enabled the reconstruction of ZnO microparticles and the reformation of Brønsted acid sites on Zn/HZSM‐5 below 200 °C. At an elevated temperature (300 °C), Zn+ species were produced by the reduction of [ZnOZn]2+ as confirmed by in‐situ Zn K‐edge extended X‐ray absorption fine structure (EXAFS) study and density functional theory (DFT) calculation. After H2 pretreatment at 300 °C, the increase in the amount of ZnOH+ species increased the selectivity of Zn‐containing ZSM‐5 for aromatics from 62 % to 67 %.

Preserving the Active Cu–ZnO Interface for Selective Hydrogenation of CO2 to Dimethyl Ether and Methanol

“…Noticeably, as the reaction went on, the intensity of both the peaks gradually increased, with their energies moving to the higher direction (from 9670.0 to 9670.7 eV and from 9673.7 to 9674.7 eV, respectively). An increase in the peak intensity and a shift of the peak to higher energies have been interpreted as indicators of the increase in the coordination number of Zn 2+ . − CO 2 and the oxygen-containing reaction intermediates are readily adsorbed on ZnO via their oxygen atom(s). , Thus, the higher energies of the Zn peaks indicated the chemisorption of CO 2 or the oxygen-containing reaction intermediates on the Zn atoms of ZnO under the working conditions. Noticeably, when the reaction gas was replaced by a stream of Ar, the intensities of ZnO peaks were decreased obviously but still higher than those of the reduced catalyst.…”

Aromatics Production via Methanol-Mediated Transformation Routes

“…175,258 Fan et al proposed that the binuclear O− Zn 2+ −O−Zn 2+ −O can be reduced in a reducing atmosphere starting above 300 °C. 258 The formation of Zn + occurring on the Zn 0 and BAS could accelerate the formation of ZnOH + , thus improving the ethene aromatization selectivity at 470 °C, from 62.3% for the nonreduced sample, to 67.4% for the reduced sample. Impregnation followed by drying and thermal treatment (calcination, reduction) is widely applied for preparing industrial supported-metal catalysts, because of its simplicity and scalability.…”

“…Copyright 1998, Elsevier. Panel (c) was adapted with permission from ref (Copyright 2012, Wiley) and ref (Copyright 2019, Wiley). Panel (e) was adapted with permission from ref .…”

“…The surface ZnO and metal–zinc were recently identified as the reactive sites for the undesired conversion of methanol to CO x and H 2 . Actually, the reduction of Zn 2+ can be achieved by the thermal treatment of Zn-ZSM-5 zeolites under hydrogen atmosphere (Figure c). , Fan et al proposed that the binuclear O–Zn 2+ –O–Zn 2+ –O can be reduced in a reducing atmosphere starting above 300 °C . The formation of Zn + occurring on the Zn 0 and BAS could accelerate the formation of ZnOH + , thus improving the ethene aromatization selectivity at 470 °C, from 62.3% for the nonreduced sample, to 67.4% for the reduced sample.…”

Meet the Women of Catalysis

“…To study the interactions between metals ions and zeolites with different crystal sizes and morphologies, an in‐situ method for characterizing the structure of catalysts by synchrotron radiation X‐ray was developed, which can be used for the preparation and activation of zeolite catalysts, and the in‐situ monitoring of their applications in methanol conversion reaction. She has published more than 50 papers in international journals and has authored more than 10 patents …”