Template-free synthesis of graphene-like carbons as efficient carbocatalysts for selective oxidation of alkanes†
Selective oxidation of aromatic alkanes by C–H activation is one of the key reactions in organic synthesis and the chemical industry. Activation of C–H bonds to obtain high-value added products under mild conditions by using sustainable carbocatalysts is of particular interest. Herein, we report a sustainable, green and template-free strategy towards the fabrication of N-doped and N/S codoped carbon nanosheets by metal-free carbonization of bioprecursors guanine and guanine sulfate. The formation of thin and N/S codoped carbon nanosheets was induced by multiple interactions of the nucleobases. Benefiting from the unique textural structure of the as-synthesized carbons, including ultrathin thickness, optimal porosity, and rich structural defects, and the synergistic coupling effect of multiple dopants, the carbon nanosheets show a high catalytic performance with 85% ethylbenzene conversion and 98% selectivity to acetophenone at 80 °C after 4 h reaction, which outperforms other equivalent benchmarks (e.g. 8.5 times higher conversion and 3.2 times higher selectivity than those of oxidized carbon nanotubes). Density functional theory simulations indicate that the oxidation of ethylbenzene is catalyzed by the synergistic effect of p-N/S and g-N/S catalysts via an OH radical mechanism. This N/S codoped strategy provides guidance for the design of carbon-based catalysts for the selective oxidation of other alkanes.