Synergistic Effect of N-Doped sp² Carbon and Porous Structure in Graphene Gels toward Selective Oxidation of C–H Bond

Abstract

N-doped carbon materials represent a type of metal-free catalyst for diverse organic synthetic reactions. However, single N-doped carbon materials perform insufficiently in the selective oxidation reaction of C−H bond compared with metal catalysts or multielement co-doped materials. There are a few reports on the application of three-dimensional (3D) carbon materials in such a reaction. Besides, the relationship between the well-developed porous structures, heteroatom doping, and their catalytic performance is unclear. In this study, 3D porous N-doped graphene aerogel catalysts with high activity and selectivity for the C−H bond oxidation under mild reaction conditions have been synthesized through a two-step method. Systematic studies on the dosage of N sources, pyrolysis temperature, and their influences on the catalytic performances have been evolved. Moreover, solid evidence of the synergistic effect of sp 2 C atoms adjacent to the N atoms and porous structure promoting the performance has been provided in this work.

Nitrogen-doped 3D hollow carbon spheres for efficient selective oxidation of C–H bonds under mild conditions

“…3d, the high-resolution C 1s spectrum of N-HCS-900 can be fit well with five peaks at 284.6, 286.0, 287.8, 289.0 and 291.5 eV, corresponding to C-C, C-N/C-O, CQO, COOH and p-p*, respectively. 14,[52][53][54] And the N-HCS-800, N-HCS-1000 and N-HPC have similar characteristic peaks of the C 1s spectra (Fig. S4b, d and f, ESI †).…”

“…The larger SSA of the carbon materials is of benefit to expose more active sites. 14 Furthermore, the pore-size distributions were calculated by the Barrett–Joyner–Halenda (BJH) method (Fig. 2c).…”

“…S8, ESI †), and the characteristic peaks in the FTIR spectra of the N-HCS-900 centered at 1245, 1435 and 1621 cm À1 are assigned to C-O, C-N and CQC, respectively. 14,55,56 After five cycles of reaction, the peaks of CQC and C-O get stronger and the peak of C-N gets weaker. The stronger CQC peak suggests that the substrates are absorbed to the catalysts, and the stronger C-O peak and the weaker C-N peak indicate the partial oxidation of the C-N bond.…”

“…[9][10][11][12] However, the application of metal-free materials is still hampered by low conversion and poor selectivity due to the high dissociation energy of the C-H bond and active side reactions. [13][14][15][16] Hence, the development of efficient metal-free catalysts is urgently required. Heteroatomdoped carbon-based materials have been considered as promising catalysts for the selective oxidation reaction of C-H bonds.…”

A Keggin-type polyoxometalate-based metal–organic complex as a highly efficient heterogeneous catalyst for the selective oxidation of alkylbenzenes

“…4,5 Hence, activating C-H bonds in materials and converting these useless materials into valuable compounds is an important, economic and green step in synthetic chemistry. 6,7 Up to now, a few catalysts such as noble metals (Pd, Ru), 1,8 non-noble metal catalysts, 9,10 earth abundant metal catalysts, 11,12 and organic molecules 13,14 have been selected for the conversion of alkylbenzenes; however, some of these are neither recyclable nor inexpensive. Therefore, an economical and efficient heterogeneous catalyst without any additives is more desirable.…”