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Gold nanoparticles supported on carbon materials for cyclohexane oxidation with hydrogen peroxide

Paper ID Volume ID Publish Year Pages File Format Full-Text
40060 45843 2013 12 PDF Available
Title
Gold nanoparticles supported on carbon materials for cyclohexane oxidation with hydrogen peroxide
Abstract

•Gold was loaded on carbon materials by sol immobilisation and double impregnation.•Au/carbon materials were tested on the oxidation of cyclohexane under mild conditions.•Au on carbon nanotubes prepared by the sol method was the most active catalyst.•Yield values comparable to the industrial process were obtained at room temperature.•High selectivity towards the formation of cyclohexanol and cyclohexanone was achieved.

Gold (1 wt.%) was loaded on several types of carbon materials (activated carbon, polymer based carbon xerogels, multi-walled carbon nanotubes, nanodiamonds, microdiamonds, graphite and silicon carbide) using two different methods (sol immobilisation and double impregnation). Samples were characterised by N2 adsorption at −196 °C, temperature programmed desorption, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectrometry, high-angle annular dark-field imaging (Z-contrast), X-ray photoelectron spectroscopy and atomic absorption spectroscopy. The obtained Au/carbon materials were used as catalysts for the oxidation of cyclohexane to cyclohexanol and cyclohexanone, with aqueous H2O2, under mild conditions. The most active catalyst was prepared by supporting gold nanoparticles on carbon nanotubes by the sol method, achieving an overall turnover number of ca. 171 and an overall yield of 3.6% after 6 h reaction time. These values are comparable to the industrial process (that uses Co catalysts and high temperature), but were obtained at ambient temperature with considerable low loads of catalyst (Au catalyst to substrate molar ratio always lower than 1 × 10−3), which is of relevance for establishing a greener catalytic process for cyclohexane oxidation. Moreover, a very high selectivity towards the formation of cyclohexanol and cyclohexanone was achieved, since no traces of by-products were detected. The promoting effect of pyrazine carboxylic acid was observed and an optimum peroxide-to-catalyst molar ratio was found to be 2 × 104. Further increase of the oxidant amount results in decreased yield due to overoxidation reactions at higher H2O2 amounts. Catalyst recycling was tested up to six consecutive cycles for the most active catalytic system (gold deposited on carbon nanotubes by sol immobilisation), and it was found that the catalyst maintains almost the original level of activity after several reaction cycles (there was only a 6% drop in activity after the sixth cycle) with a rather high selectivity to cyclohexanol and cyclohexanone and with no catalyst leaching. The differences in activity for the other samples can be explained in terms of gold nanoparticle size and the textural properties of the carbon support.

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Keywords
Gold nanoparticles; Carbon materials; Cyclohexane oxidation; Catalysis
First Page Preview
Gold nanoparticles supported on carbon materials for cyclohexane oxidation with hydrogen peroxide
Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 467, 2 October 2013, Pages 279–290
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis