Graphene Oxide: A Convenient Metal-Free Carbocatalyst for Facilitating Aerobic Oxidation of 5-Hydroxymethylfurfural into 2, 5-Diformylfuran

Abstract

By thermal treatment in vacuum, graphite oxide prepared from Hummers' method was exfoliated and partially reduced. This procedure imparts the graphene oxide (GO) the high reactivity with 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) as co-catalyst for selective oxidation of 5-hydroxymethylfrufural (HMF) to 2, 5-diformylfuran (DFF) under certain conditions (100% HMF conversion with HMF selectivity 99.6% at 80 wt.% GO loading, 1 atm air pressure). This study found that GO could function as an oxidant for anaerobic oxidation of HMF during which carboxyl groups in GO were reduced. Importantly, the partially reduced GO material could continue activate molecular oxygen during aerobic oxidation. Further study showed that oxygen functionalities in GO material had a crucial effect on the catalytic oxidation of HMF.By control experiments and molecular analogues tests, a plausible mechanism was proposed in which the high reactivity was attributed to the synergistic effect of the carboxylic acid groups and unpaired electrons at GO edge defects, with TEMPO as the co-catalyst and oxygen as the terminal oxidant.

Carbon Catalyzed Hydroxylation of Benzene with Dioxygen to Phenol over Surface Carbonyl Groups

“…The I D /I G values of NOC‐m are in the range of 0.83∼0.88, suggesting that their defects density is close to each other . ESR spectra (Figure S7) showed a broad peak attributable to the unpaired spins at the edges of graphitic carbon network ,…”

“…Various factors affect the catalytic performance of carbons, such as the surface area, chemical composition (e. g. N, P or B substitution), defects (e. g. zig‐zag and armchair edges), and surface groups (e. g. oxygen groups) ,,,. Correlation of the structural information and the activities of the carbons above suggest that the surface area, N content and defects are not the determining parameters for the activity (Table and Figure S21).…”

“…By virtue of these, we propose a possible reaction route for the present hydroxylation reaction (Scheme d): O 2 is chemosorbed on the surface of carbon and then activated by the surface O species (mainly carbonyl groups) to produce the reactive hydroxyl radicals, which oxidize the benzene to furnish the product phenol. Previously, several active sites such as defects, edge sites (zig‐zag and armchair edges), heteroatoms and surface functional groups have been proposed for O 2 activation via the following mechanisms: 1) O 2 was reduced to peroxo and superoxide species by carbon π electrons and this activation mode was enhanced after incorporating heteroatoms; 2) superoxide species was formed through the O 2 reduction by the edge sites with unpaired electrons and acted as the oxidant; 3) the surface oxygen groups such as quinone were the active sites to react with the substrate and then regenerated by O 2 ,. In our hydroxylation reaction, O 2 was activated by the surface O species rather than carbon π electrons to generate the hydroxyl radicals as the reactive oxygen species; superoxide species was not involved in the reaction, as illustrated by the radical quenching experiment; the inert activity in the anaerobic reaction excludes the inclusion of the surface O species in the first step of the reaction.…”

Benzoic Acid/TEMPO as a Highly Efficient Metal‐Free Catalyst System for Selective Oxidation of 5‐hydroxymethylfurfural into 2, 5‐diformylfuran

“…[1][2][3][4][5][6] One of the most attractive directions in biorefinery developmenti sd evotedt ot he production of furan derivatives, such as furfural and 5-hydroxymethylfurfural (HMF). [7,8] HMF,w hich is ap roduct of C6-based carbohydrates,i s widely considered as av ersatilep latform chemical for the productiono fabroad range of fine chemicals, [9] pharmaceuticals, [10] and liquid transportation fuels. [10][11][12] Selective oxidation of HMFi so ne of the most essential transformations in the biorefinery.…”

Cr‐MIL‐101‐Encapsulated Keggin Phosphomolybdic Acid as a Catalyst for the One‐Pot Synthesis of 2,5‐Diformylfuran from Fructose

“…MIL-101 has been widely used in the oxidation of hydrocarbons, such as cyclohexene,i ndane, and dibenzothiophene. [31] In addition, it was reported that the acids formed by the thermolysis of DMSO may act as catalysts in the oxidation of HMF. [31] In addition, it was reported that the acids formed by the thermolysis of DMSO may act as catalysts in the oxidation of HMF.…”