Methanol Conversion on MFI Zeolites Obtained in Fluoride Medium: Effect of Silicon Source
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thanol Conversion on MFI Zeolites Obtained in Fluoride Medium: Effect of Silicon Source V. S. Pavlova, *, D. V. Brutera, S. V. Konnova, and I. I. Ivanovaa, b a
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia b Faculty of Chemistry, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received March 11, 2020; revised April 6, 2020; accepted April 10, 2020
Abstract—The work is aimed at a fundamental study of the formation of acid sites in MFI zeolites obtained in a fluoride medium using Aerosil, silica gel, and silica sol as sources of silicon. The synthesized samples have been characterized by a set of instrumental methods and tested in the reaction of methanol conversion to hydrocarbons. It has been shown that the synthesis of MFI zeolite in a fluoride medium leads to the insertion of aluminum into the tetrahedral positions of the zeolite framework to form isolated acid sites. Moreover, the type of amorphous source of silicon affects both the amount of incorporated aluminum and the size of the product crystals. It has been established that the use of silica sol as a silicon source leads to an increase in the catalyst time-on-stream stability and a decrease in the selectivity for ethylene. The obtained result is explained by an increase in the proportion of Al atoms localized in zeolite channels. Keywords: conversion of methanol to hydrocarbons (MTH), zeolite synthesis, zeolite catalysis, MFI zeolite DOI: 10.1134/S0965544120080095
The conversion of methanol to hydrocarbons (MTH, methanol-to-hydrocarbons) is the main process for synthesizing lower olefins for the polymer industry, fuel components, and aromatic hydrocarbons from feedstock other than petroleum refining products. The study of this process began with its discovery in 1977 by Mobil researchers using an MFI zeolite catalyst [1]. The implementation of this process is especially important for regions remote from large oil fields (New Zealand, South Africa) and countries with significant reserves of coal and gas (Bahrain, China). An increase in the importance of this process in the future is likely for other countries in view of the depletion of oil reserves. Currently, Shenhua Baotou Coal Chemical is actively implementing the MTH technology on the industrial scale in China under scientific supervision by the Dalian Institute of Chemical Physics of the PRC Academy of Sciences [2]. Investigations of the MTH process using various zeolite and zeolite-like materials showed that mesoporous zeolites with the MFI and MEL structure have their time-on-stream stability one to two orders of magnitude longer than that of both microporous (CHA, AEI, etc.) and macroporous (FAU, BEA, etc.) structures [3]. Moreover, the detailed mechanism of their deactivation and its relation with the structure and localization of active sites remains under debate and is still poorly understood. In particular, based on
the study of the catalytic properties of a large number of samples, Barbera et al. [4] showed that it
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