作为原子经济的反应,通过CH3OH和碳酸亚乙酯(EC)的酯交换直接生成碳酸二甲酯(DMC)和乙二醇(EG)具有多种应用前景,但是,探索具有高比表面积的载体和具有更多基本位点的新型多相催化剂仍然是一个长期的研究挑战。为此,在这里,氮掺杂的中孔碳(NMC,439m2/g)基K-O2路易斯碱催化剂(K-O2/NMC),具有良好分散的强碱性位点(2.23mmol/g,84.5%)进行了设计和合成。通过傅里叶变换红外光谱对NMC和K-O2/NMC的组成和结构进行了全面的研究,X射线衍射,X射线光电子能谱,扫描电子显微镜,透射电子显微镜,N2吸附-解吸,CO2程序升温解吸,和接触角测量。使用第一性原理计算模拟了K-O2/NMC催化剂的最佳结构构型和电子云分布。电子转移主要表现为从K-O到C-O/C-N的流动,每个原子之间的原子间相互作用增强,并在重新分布后表现出更稳定的状态。此外,CH3OH在K-O-O和K-O-N位点的吸附能(Eads)分别为-1.4185eV和-1.3377eV,分别,CH3OH中的O原子在K-O-O位点对K原子表现出较强的吸附趋势。在最优条件下,EC转换,DMC/EG选择性,周转次数/频率为80.9%,98.6%/99.4%,和40.5/60.8h-1,分别为反应速率常数(k)为0.1005mol/(L·min)。结果表明,本文制备的非均相K-O2/NMC催化剂在保证催化效果的同时,大大降低了反应成本,整个系统需要较低的反应温度(65°C),较短的反应时间(40分钟),和较低的催化剂量(2.0wt%的EC)。因此,K-O2/NMC可以在不同的酯交换反应中用作催化剂。
As an atom-economical reaction, the direct generation of dimethyl carbonate (DMC) and ethylene glycol (EG) via the
transesterification of CH3OH 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 m2/g) based K-O2 Lewis base catalyst (K-O2/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-O2/NMC were comprehensively investigated via Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, CO2 temperature-programmed desorption, and contact angle measurements. The optimal structural configuration and electron cloud distribution of the K-O2/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 (Eads) of CH3OH at K-O-O and K-O-N sites were -1.4185 eV and -1.3377 eV, respectively, and the O atom in CH3OH 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-O2/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-O2/NMC can be used as a catalyst in different
transesterification reactions.