Epoxidation of trans-stilbene with molecular oxygen over an eco-friendly heterogeneous cobalt oxide/reduced graphene oxi
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Epoxidation of trans‑stilbene with molecular oxygen over an eco‑friendly heterogeneous cobalt oxide/reduced graphene oxide composite material Surjyakanta Rana, et al. [full author details at the end of the article] Received: 26 April 2020 / Accepted: 10 July 2020 © Springer Nature B.V. 2020
Abstract We report the synthesis of 1, 5, 10 wt% cobalt oxide/reduced graphene oxide (CoO– RGO) composite materials by a simple solvothermal method. We assessed their catalytic activity in liquid phase epoxidation reaction without any sacrificial reductant and fully characterised the prepared catalysts by different techniques, including powder XRD, Raman spectra, scanning electron microscopy, transmission electron microscopy and ICP-MS. 5 wt% Cobalt oxide (CoO–RGO-5) promoted material showed high conversion (57%) of trans-stilbene oxide and excellent selectivity (96%) towards trans-stilbene epoxidation in DMF solvent by using the molecular oxygen as an oxidant. The conversion efficiency of trans-stilbene reaction remained the same for fresh and recycled catalysts after the 4th run. Graphic abstract
Keywords Reduced graphene oxide · Cobalt · Epoxidation · Trans-stilbene · Heterogeneous catalyst
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Introduction Epoxides are the most important intermediates in the preparation of a gamut of chemicals, materials, and pharmaceuticals [1, 2]. Currently, epoxides are mainly produced by using either organic peracid as an oxidant or many chemicals, which are not economical and environmentally friendly [3, 4]. An alternative approach is to use the recyclable heterogeneous solid catalysts together with good oxidants, such as molecular oxygen, TBHP, and hydrogen peroxide [5, 6]. Based on the literature review, cobalt-based materials exhibit excellent catalytic performance for epoxidation reactions [7–10]. Yang et al. have reported 92.6% conversion and 92.6% selectivity towards trans-stilbene epoxide over Co-substituted TUD-1 mesoporous material with molecular oxygen, at 100 °C for 10 h [11]. Tang et al. reported the covalently bonded cobalt(II) acetylacetonate (Co(acac)2) on SBA-15 as a catalyst for the epoxidation of trans-stilbene with molecular oxygen. The reaction at 100 °C for 6 h archived up to 50.1% conversion with 96.7% selectivity towards trans-stilbene epoxide [12]. Farzaneh et al. explored Co(acac)2 complexes within nanoreactors of Al-MCM-41 as the catalyst for epoxidation of trans-stilbene. They observed a 99% conversion and 80% selectivity towards epoxide product in the presence of molecular oxygen at 12 h. Also, Co(bpy)2Cl2 complexes with Al-MCM-41 catalyst were reported to give 87% conversion and 70% selectivity of epoxide products at 12 h [13]. Choi et al. described the epoxidation of trans-stilbene with high yield (0.32 mM) of trans-stilbene oxide with potassium monopersulfate and cobalt-containing polyoxotungstate as a catalyst at pH 5 [14]. Islam et al. reported that Schiff base cobalt complex catalysed reaction gave 62% conversion of trans-stilbene and 70% selectivity towa
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