Design of nitrogen-doped graphitized 2D hierarchical porous carbons as efficient solid base catalysts for transesterification to biodiesel

Abstract

Two-dimensional (2D) nanomaterials usually show good mass transportation and enhanced accessibility of located active sites in the areas of adsorption, separation and heterogeneous catalysis. We herein report nitrogen-decorated 2D hierarchical nanoporous carbonaceous (N-HPC-Ts) solid bases synthesized by one-step carbonization of a solid mixture of urea and chitosan. The N-HPC-Ts have large BET surface areas (202–641 m² g⁻¹) and a partially graphitized carbon framework and show good hydrophobicity and enhanced wettability for organic compounds such as sunflower oil, methanol and benzaldehyde. Moreover, N-HPC-Ts have nitrogen concentrations up to 15.9 mmol g⁻¹ with a high ratio of pyridinic nitrogen (∼68.7%). Therefore, the N-HPC-Ts can be used as highly efficient and reusable solid bases in base-catalyzed reactions such as transesterification to produce biodiesel and Knoevenagel condensation to produce fine chemicals, and their activities are much better than many reported solid acid and base catalysts such as H₃PW₁₂O₄₀, commercial Amberlite-400 base resin, hydrotalcite and CaO. To the best of our knowledge, there are still few reports on the direct use of 2D carbonaceous solid bases in catalyzing biodiesel production. The excellent activities of N-HPC-Ts benefit from their structural characteristics such as high concentrations of base sites, good wettability for various reactants and unique 2D hierarchical porous structures.