期刊
CHEMICAL ENGINEERING JOURNAL
卷 474, 期 -, 页码 -出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.cej.2023.145918
关键词
Melamine-based polymers; Metal; and halogen -free; Heterogeneous catalyst; CO 2 cycloaddition; Density functional theory
This study investigated the catalytic activity of two melamine-based organic polymers, UM-OP and AM-OP, for the cycloaddition of CO2 with epoxides. The results revealed the mechanism of N sites and -NH- groups in triggering the reaction of epoxides, providing a reference for the design of metal- and halogen-free heterogeneous catalysts.
The development of highly efficient and metal- and halogen-free heterogeneous catalysts for the chemical conversion of CO2 to cyclic carbonates plays a critical role in the reduction of greenhouse gas emissions. Herein, two melamine-based organic polymers namely UM-OP and AM-OP with abundant N sites and -NH- groups were synthesized by a facile method and their activity for cycloaddition of CO2 with epoxides was investigated. The structural analysis shows that the UM-OP and AM-OP catalysts were composed of specially designed urea and amide group linkages, respectively. UM-OP and AM-OP are metal-free, halogen-free, and can efficiently catalyze CO2 cycloaddition under solvent-free and cocatalyst-free conditions. Moreover, the UM-OP catalyst exhibited higher catalytic activity than AM-OP, good structural stability, recyclability, separability from the products, and shown high activity to a series of epoxides. The density functional theory (DFT) calculations revealed the activation of epoxides by -NH- groups and CO2 by N sites in the samples, respectively, and N sites can also act as nucleophiles to realize ring opening of epoxides. Combining the results of experiments and calculations, it was further found that the double -NH- (urea group) is more efficient than single -NH- (amide group) to activate the epoxides. This paper reveals the mechanism of N sites and -NH- groups synergistically catalyzing the CO2 cycloaddition, and further supports the theory that N atoms acts as nucleophile for ring opening, providing a reference for the design of metal- and halogen-free heterogeneous catalysts.
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