Solvent-Free Production of ε-Caprolactone from Oxidation of Cyclohexanone Catalyzed by Nitrogen-Doped Carbon Nanotubes

摘要

As an important raw material for the synthesis of polycaprolactone, a significant alternative for the non-degradable plastic, epsilon-caprolactone (epsilon-CL) monomer is typically produced through the Baeyer-Villiger oxidation of cyclohexanone (Cy = O). In this work, a solvent-free, highly efficient, and nonmetallic catalytic system was developed to produce the epsilon-CL monomer with dioxygen as the oxidant and benzaldehyde (BEA) as the co-oxidant. Nitrogen-doped carbon nanotubes (NCNTs) as the catalyst boost the catalytic activity (10.09% conversion, 10.06% yield of epsilon-CL), much higher than other carbon catalysts. The normalized specific activity of NCNTs reached 2964.80 mmol/g/h and 20.02 mmol/m(2)/h, which are 2-4 orders of magnitude higher than the state-of-the-art catalysts. The structure-dependent activity result shows that the ratio between pyridine nitrogen (N-P) and graphite nitrogen (N-G) on the surface of NCNTs positively affects the catalytic performance. Oxygen functionalities on the NCNT surface inhibit the activity by suppressing the auto-oxidation of BEA, which unexpectedly increases aldehyde efficiency. Finally, this process could be scaled up to a molar-scale reaction with a similar activity, which lays down the foundation of the industrial application of the solvent-free Baeyer-Villiger oxidation catalyzed by nanocarbons.

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