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Big effect of a small change: formation of CuO nanoparticles instead of covalently bound Cu(II) over functionalized mesoporous silica and its impact on catalytic efficiency

Abstract

Two different heterogeneous catalysts, one with Cu(II) covalently bonded to functionalized mesoporous silica (FMS-Cu(II)) and another with CuO nanoparticles immobilized over the same silica (FMS-CuO-np), have been synthesized by a common route but with minor alteration of sequence of addition of the reagents. It is interesting to find that by merely changing the order of addition of reagents Cu(II) can be incorporated into the framework in two different forms. In one case Cu(II) binds to the N and O donor centers present in the functionalized material whereas in other CuO nanoparticles are generated in situ. The materials have been thoroughly characterized by powder X-ray diffraction, nitrogen adsorption/desorption, transmission electron microscopy, thermal analysis and FT-IR, solid state MAS-NMR and atomic absorption spectrophotometric studies. The synthesized products have been tested for their catalytic efficiencies in the oxidation of olefins, as a model case. Styrene, α-methyl styrene, cyclohexene, trans-stilbene and cyclooctene have been used as substrates in the presence of tert-butyl hydroperoxide as the oxidant in acetonitrile medium under mild conditions. The products of the catalytic studies have been identified and estimated by gas chromatography and gas chromatography-mass spectrometer. The rate of conversion of the substrates for both the catalysts is high and selectivity is also good. But from comparative studies, it is found that FMS-CuO-np which contains CuO nanoparticles shows better efficiency over FMS-Cu(II). The catalysts have been recycled for five catalytic cycles without showing much drop in their catalytic activity.

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Article information


Submitted
28 May 2020
Accepted
26 Jun 2020
First published
30 Jun 2020

Dalton Trans., 2020, Accepted Manuscript
Article type
Paper

Big effect of a small change: formation of CuO nanoparticles instead of covalently bound Cu(II) over functionalized mesoporous silica and its impact on catalytic efficiency

T. Das, D. Singha and M. Nandi, Dalton Trans., 2020, Accepted Manuscript , DOI: 10.1039/D0DT01922D

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