Self-catalyzed cycloaddition of CO2 and epoxides over covalent organic frameworks without adding solvent and co-catalyst
Authors: Jingwen Yang, Zhengyan Qu, Jiuxuan Zhang, Hong Jiang, Zhenchen Tang, Weihong Xing, Rizhi Chen
The cycloaddition of CO2 and epoxides to synthesize cyclic carbonates is a key strategy for CO2 utilization, though heterogeneous catalysts often suffer from instability. Covalent organic frameworks (COFs) present a compelling alternative due to their excellent textural properties and abundant Lewis basic sites. Herein, triazine-based COFs (PC-COFs) were synthesized by optimizing reaction time and temperature and were applied to catalyze the CO2 cycloaddition with epichlorohydrin (ECH) under solvent-free conditions, Instead of necessity of adding homogeneous co-catalyst, this study reveals a synergistic self-catalysis mechanism, where the carbonate product adsorbed on the Lewis basic PC-COF surface forms catalytic pairs with Lewis acidic carbonates, significantly accelerating the reaction. After five cycles, catalytic activity increased by 35% from 56.2% to 91.4%, and stabilizing over seven cycles. Under optimal reaction conditions, PC-COF-50-30 demonstrated outstanding catalytic performance, with a 98.7% ECH conversion, 97.6% selectivity to ECH carbonate and a CO2 conversion rate of 9.0 g‧g−1·h−1. This work provides a valuable example of high-performance CO2 cycloaddition catalysts and a strategy to achieve enhanced catalytic efficiency through product-catalyst synergy.
