Selectively oxidized carbon nanocatalysts for the oxidation of cis-cyclooctene

• Type: Article in International Scientific Journal
• Date: 2018

Authors

Jarrais, B (Author) Other; Guedes, A (Author) FCUP; Cristina Freire (Author) FCUP

Journal

Title: New Journal of Chemistry

Vol. 42

Pages: 2306-2319

ISSN: 1144-0546

Publisher: Royal Society of Chemistry

Indexing

ISI Web of Knowledge - 8 Citations

Scopus - 7 Citations

Other information

Authenticus ID: P-00N-JKE

DOI: 10.1039/c7nj03706f

Abstract (EN): 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 using three different oxidation procedures: (i) nitric acid treatment; (ii) nitric acid followed by thermal treatment at 400 degrees C; (iii) gas phase oxidation with O-2, 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 mu mol g(-1), respectively, for material MWCNTh, and 612, 120, and 1392 mu mol g(-1), respectively, for material GFh; the nanomaterials treated with nitric acid followed by thermal treatment at 400 degrees C (MWCNTht and GFht) presented a loss of carboxylic acids and an increase in carboxylic anhydride content (36 and 132 mu mol g(-1), respectively, for material MWCNTht, and 36 and 156 mu mol 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 mu mol g(-1), respectively, for material MWCNTo, and 804, 420, and 144 mu mol g(-1)1, respectively, for material GFo. The carbon nanocatalysts showed activity in the selective oxidation of cis-cyclooctene to epoxycyclooctane using mild conditions: hydrogen peroxide was used as oxidant at 80 degrees C. The modifications introduced in the pristine materials through nitric acid followed by thermal treatment at 400 degrees C originated the nanocatalysts with the 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 14