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Selectively oxidized carbon nanocatalysts for the oxidation of cis-cyclooctene

Abstract

In this work, selectively oxidized carbon nanotubes and graphene flakes were used as carbocatalysts in the mild oxidation of cis-cyclooctene. Firstly, the multi-walled carbon nanotubes and graphene flakes were oxidized through three different oxidation procedures: (i) nitric acid treatment; (ii) nitric acid followed by thermal treatment at 400 C; (iii) gas phase oxidation with O2 and subsequently characterized by several techniques. Both oxidized nanomaterials showed an overall increase in the oxygen content and revealed that the different oxidation procedures promoted different superficial chemical compositions: nitric acid treated carbon nanotubes and graphene flakes (respectively, MWCNTh and GFh), presented increased amounts of carboxylic acids, anhydrides and phenols up to 552, 84, and 648 µmol g-1, respectively, for material MWCNTh, and 612, 120, and 1392 µmol g-1, respectively, for material GFh; the nanomaterials treated with nitric acid followed by thermal treatment at 400 ˚C (MWCNTht and GFht), presented a loss of carboxylic acids and an increase in carboxylic anhydrides content (36 and 132 µmol g-1, respectively, for material MWCNTht, and 36 and 156 µmol g-1, respectively, for material MWCNTht), when compared to the nitric acid treated materials MWCNTh and GFh; and finally the gas phase treated nanomaterials, MWCNTo and GFo, presented an increase in the amounts of phenols, carbonyls/quinones, and lactones up to 720, 216, and 144 µmol g-1, respectively, for material MWCNTo, and 804, 420, and 144 µmol g-1, respectively, for material GFo. The carbon nanocatalysts showed to be active in the selective oxidation of cis-cyclooctene to epoxycyclooctane using mild conditions: hydrogen peroxide as oxidant at 80 ˚C. The modifications introduced in the pristine materials, through nitric acid followed by thermal treatment at 400 ˚C, originated the nanocatalysts with best activity and selectivity: MWCNTht presented 47% of substrate conversion and 79% epoxycyclooctane selectivity whereas GFht showed 57% conversion and 85% epoxycyclooctane selectivity. Reusability experiments revealed no loss of catalytic activity up to three catalytic cycles. The results indicate that the fine tuning of the carbon nanomaterials through appropriate oxidation procedures, is crucial in achieving metal-free carbocatalysts with enhanced performance and selectivity in selective oxidation reactions.

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Publication details

The article was received on 28 Sep 2017, accepted on 07 Jan 2018 and first published on 08 Jan 2018


Article type: Paper
DOI: 10.1039/C7NJ03706F
Citation: New J. Chem., 2018, Accepted Manuscript
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    Selectively oxidized carbon nanocatalysts for the oxidation of cis-cyclooctene

    C. Freire, B. Jarrais and A. Guedes, New J. Chem., 2018, Accepted Manuscript , DOI: 10.1039/C7NJ03706F

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