Synthesis of three-dimensional nitrogen doped meso/macroporous carbon beads for heterogeneous catalytic solvent-free oxidation of ethylbenzene

Abstract

A series of nitrogen doped 3D hierarchically porous carbon beads with size of 0.6–0.9 mm are successfully prepared by one-step pyrolysis of dicyandiamide and macroporous resin under different ratio. Dosage of dicyandiamide can effectively control shrinkage of resins during pyrolysis, and favor to create 3D interconnected pore channels and abundant nitrogen doped sites as a self-sacrificing dopant and activating-like agent. The beads display excellent conversion for ethylbenzene to acetophenone as opposed to only calcinating pristine IRA resins (83.5% vs 12.1%), when the ratio reach 1:1. At initial reaction period, linear relationships between concentration of reactants and products are established to evaluate whether the beads are provided with diffusion limitation in mentioned reaction. Structural characterization and reaction kinetic studies indicate that the larger mesoporous pore volume and more meso/macro-pore structure of the beads can expose more accessible active sites and lower diffusion limitation, significantly affecting the initial rates, thereby improving the catalytic performance. In addition, macro-beads in size of millimeter scale can effectively exert the advantages of easy separation and recovery. A new strategy is provided which can keep the diversity of pore scale in porous carbonous precursors during pyrolysis, thereby more effectively applying in heterogeneous catalysis.