Features of the Mechanism of the Dimethyl Ether to Light Olefins Conversion over MgZSM-5/Al 2 O 3 : Study by Vibrational
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Features of the Mechanism of the Dimethyl Ether to Light Olefins Conversion over MgZSM‑5/Al2O3: Study by Vibrational Spectroscopy Experimental and Theoretical Methods G. N. Bondarenko1 · A. S. Rodionov1 · N. V. Kolesnichenko1 · T. I. Batova1 · E. N. Khivrich1 · A. L. Maximov1 Received: 20 July 2020 / Accepted: 17 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Features of the mechanism of dimethyl ether (DME) conversion to olefins over ZSM-5 zeolite catalysts were studied using experimental and theoretical methods of vibrational spectroscopy. A catalytic activity comparison of the catalysts Mg l2O3 (by weight) as a binder in HZSM-5 without a binder and Mg-HZSM-5/Al2O3 containing 1% Mg (by weight) and 33% A the DME conversion was carried out. Using high-temperature diffuse reflectance IR (DRIR) spectroscopy in situ combined with quantum-chemical simulations in the temperature range of 25–450 °C in a stream of dry Ar and DME, the bands corresponding to OH bonds, including BAS and H 3O+, were interpreted. Depending on the temperature and the presence of magnesium and a binder in the catalyst composition, the intensity and position of these bands maxima vary greatly. The intermediates of the catalytic DME conversion were discovered and identified. At low temperatures (below 200 °C), in a DME stream, methoxy groups ( CH3O-Al-), ketene ( CH2 =C=O), and a carbocation ( CH3 +) were formed on the surface of the catalysts. As the temperature rises (above 300° C), the bands from ketene completely disappear in the spectra of catalysts, and bands from oxonium cations or ylide particles appear, leading the process of DME conversion by the oxonium-ylide mechanism. In the presence of H3O+, the conversion of DME on the zeolite catalyst surface was more effective; however, selectivity for olefins was lower.
* T. I. Batova [email protected] 1
Russian Academy of Sciences A.V.Topchiev Institute of Petrochemical Synthesis, Leninsky Prospect, 29, Moscow 119991, Russia
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Graphical Abstract
Keywords Dimethyl ether · Light olefins · Mechanism · Experimental and theoretical methods of vibrational spectroscopy · Zeolite catalysts
1 Introduction The synthesis of light olefins like ethylene and propylene from natural gas through intermediate production of oxygenates opens up still more possibilities for industrial application. The conversion of natural gas into light olefins usually includes the stage of synthesis-gas obtaining, followed by the conversion of synthesis-gas into hydrocarbons via methanol. This process is brought to commercial use and is now being actively introduced into the industry by a number of firms and allows to obtain ethylene and/or propylene with high yields; as to the efficiency, it surpasses the traditional industrial pyrolysis of light oil fractions, due to the lower temperature used at the stage of synthesis of olefins and higher selectiveness on ethylene and propylene. Along with the commercial technolo
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