Catalytic epoxidation of propylene over a Schiff-base molybdenum complex supported on a silanized mesostructured cellula
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Catalytic epoxidation of propylene over a Schiff‑base molybdenum complex supported on a silanized mesostructured cellular foam Dawei Chen1 · Xiaoyu Zhang1 · Haoran Jiang1 · Xia Yuan1 Received: 20 June 2020 / Accepted: 3 August 2020 © Springer Nature B.V. 2020
Abstract A Schiff-base molybdenum complex (MoO2–salen) supported on mesostructured cellular foam (MCF) was initially prepared by an in situ synthesis method under acidic conditions. Following silanization modification, a M oO2–salen@MCF-S sample with improved surface hydrophobicity was obtained. The ligand environment of molybdenum within the samples has been analyzed by Fourier-transform infrared spectroscopy, ultraviolet/visible spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, the textural and structural properties of the corresponding materials have been characterized by nitrogen adsorption–desorption isotherms and transmission electron microscopy. Despite of the presence of fewer M oO2 species, the results showed that M oO2–salen@MCF-S has more active Mo centers than MoO2–salen and MoO2–salen@MCF on the basis of maintaining the mesoporous structure. The catalytic performances of the synthesized samples were assessed in the epoxidation of propylene with tert-butyl hydroperoxide (TBHP) as an oxidant, and the mechanism of propylene epoxidation under M oO2–salen@MCF was given. The prepared MoO2–salen@MCF-S material showed the best epoxidation performance with 1,2-dichloroethane as a solvent and a molar ratio of propylene to TBHP of 10:1 at 120 °C, giving a TBHP conversion of up to 100% after 1 h, with selectivities for propylene oxide and tert-butyl alcohol reaching 94.7% and 84.6%, respectively. Keywords Mesostructured cellular foam · Propylene epoxidation · Schiff-base molybdenum complex · Silanization modification
* Xia Yuan [email protected] 1
School of Chemical Engineering, Xiangtan University, Xiangtan 411105, Hunan, China
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Introduction Propylene oxide (PO) is an important industrial raw material for the production of waterproof materials, coatings, and other products [1]. Due to its high potential application value and economic value, the production process is constantly developing and progressing [2–4]. Several methods are used for the conversion of propylene to propylene oxide, including chlorohydrination, co-oxidation, and hydrogen peroxide direct oxidation [5]. The chlorohydrin method has gradually been eliminated due to pollution problems [6]. At present, the main process used in industry is the co-oxidation method, which involves oxidation of a third substance to obtain a predetermined oxygen source, and then, the propylene epoxidation reaction is carried out with this oxygen source to finally form propylene oxide and the corresponding by-product. Compared with the ethylbenzene cooxidation process using ethylbenzene hydroperoxide as the oxygen source, the isobutane co-oxidation process with tert-butyl hydroperoxide (TBHP) as the oxygen source is more mature [7]. The catal
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