Application of Mesoporous Carbon-Based Highly Dispersed K–O₂ Strong Lewis Base in the Efficient Catalysis of Methanol and Ethylene Carbonate

Abstract

As an atom-economical reaction, the direct generation of dimethyl carbonate (DMC) and ethylene glycol (EG) via the transesterification of CH 3 OH and ethylene carbonate (EC) has several promising applications, but the exploration of carriers with high specific surface areas and novel heterogeneous catalysts with more basic sites remains a long-standing research challenge. For this purpose, herein, a nitrogen-doped mesoporous carbon (NMC, 439 m 2 /g) based K−O 2 Lewis base catalyst (K− O 2 /NMC) with well-dispersed strongly basic sites (2.23 mmol/g, 84.5%) was designed and synthesized. The compositions and structures of NMC and K−O 2 /NMC were comprehensively investigated via Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N 2 adsorption− desorption, CO 2 temperature-programmed desorption, and contact angle measurements. The optimal structural configuration and electron cloud distribution of the K−O 2 /NMC catalyst were simulated using first-principles calculations. The electron transfer predominantly manifested as a flow from K−O to C−O/C−N, and the interatomic interactions between each atom were enhanced and exhibited a tendency for a more stable state after redistribution. Furthermore, the adsorption energies (E ads ) of CH 3 OH at K− O−O and K−O−N sites were −1.4185 eV and −1.3377 eV, respectively, and the O atom in CH 3 OH exhibited a stronger adsorption tendency for the K atom at the K−O−O site. Under the optimal conditions, the EC conversion, DMC/EG selectivity, and turnover number/frequency were 80.9%, 98.6%/99.4%, and 40.5/60.8 h −1 , respectively, with a reaction rate constant (k) of 0.1005 mol/(L•min). Results showed that the heterogeneous K−O 2 /NMC catalyst prepared herein greatly reduced the reaction cost while guaranteeing the catalytic effect, and the whole system required a lower reaction temperature (65 °C), a shorter reaction time (40 min), and a lower catalyst amount (2.0 wt % of EC). Therefore, K−O 2 /NMC can be used as a catalyst in different transesterification reactions.