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Novel environmentally benign urea derivative-based ILs were successfully prepared and characterized, and displayed exceptional performances for both CO2 capture and CO2 catalytic conversion under metal-, cocatalyst- and solvent-free conditions.

A novel Lewis acid–base bifunctional Zn­(II)-based MOF-Zn-1 [Zn2L2MA·2DMF] (MA = melamine, H2L = 2,5-thiophenedicarboxylic acid), with abundant micropores and free -NH2 groups was facilely assembled by incorporating zinc­(II) ion with nitrogen-rich melamine and 2,5-thiophenedicarboxylic acid ligands. The constructed MOF-Zn-1 presented an excellent affinity toward CO2 molecules due to the Lewis-base property together with abundant micropores. The Zn active sites could be used for epoxide activation. The acid–base synergistic effects facilitated CO2 conversion into cyclic carbonates under ambient temperature using the porous MOF-Zn-1 as a heterogeneous catalyst. Moreover, the MOF-Zn-1 exhibited satisfied stability and versatility, and it was easy to recycle with no obvious decrease of catalytic activity. Then the feasible synergistic mechanism of MOF-Zn-1/Bu4NBr catalysts for CO2 conversion was proposed.

The development of efficient and green protocol for recycling of waste plastics is of great significance in terms of “sustainable society” and “green chemistry” concepts. Several ionic liquids (ILs) with different acidity–basicity and structures were one-step synthesized and characterized. They were applied to alcoholysis of polycarbonate (PC) without metal and solvent. The IL structures and reaction conditions were optimized. Moreover, the alcohol scopes and catalyst reusability were evaluated. The results showed that 100% PC conversion and 99% bisphenol A (BPA) yield were obtained by using [HDBU]­[LAc] catalyst, and the [HDBU]­[LAc] could keep high-activity after using for six times under the optimized conditions. Finally, the possible reaction mechanism was proposed via the FT-IR and NMR analysis technique.

Polyester wastes have caused a series of environmental issues, and it has became imperative to promote recycling of polyester wastes. Herein, a novel protocol for polyester depolymerization to recover the corresponding monomers or chemicals catalyzed by imidazole-anion-derived ionic liquids (ILs) was developed. The catalytic behavior, catalyst recyclability, and versatility for alcoholysis of polyester were studied in detail under mild and green conditions. A comparison of the activity with the reported catalysts was provided, which indicated the unparalleled activity of [HDBU][Im] for the polyester alcoholysis. An in-depth study of the feasible alcoholysis mechanism was given assisting with in situ analysis technique. The developed protocol realized the highly efficient chemical recycling of polyesters via alcoholysis method with unparalleled activity, avoided the pollution caused by toxic transition metal ions and organic solvents, indicating a green and promising alternative for practical recycling of polyester wastes.

Abstract:The combination of metal modified SBA-15 catalyst with potassium iodide was developed as heterogeneous dual catalysts for chemical fixation of CO2 to cyclic carbonates. It was observed that the binary Zn-SBA-15/KI catalysts were the most efficient among various metal modified SBA-15/KI catalysts and showed excellent synergetic effect in promoting the reaction under mild conditions. Moreover, the effects of reaction parameters on cycloaddition of CO2 with propylene oxide (PO) to propylene carbonate (PC) were optimized. Under the optimal conditions determined, Zn-SBA-15/KI catalytic system was also versatile to CO2 cycloaddition with other epoxides.Additionally, the mechanistic details for the fixation of CO2 into cyclic carbonate catalyzed by SBA-15/KI and Zn-SBA-15/KI were also contrastively elucidated using the density functional theory (DFT) method. The DFT results suggested that zincmodified and unmodified catalysts showed different coupling modes of CO2, and the ‡ These authors contributed equally to this work. -2-ring-opening reaction was the rate-determining step in the SBA-15/KI catalyzed cycloaddition reaction, but the zinc-modified SBA-15/KI catalysts could enhance the CO2 cycloaddition as the formation of a stable complex which was beneficial to CO2 trapping. As a result, the ring-closing reaction became the rate-determining step in the Zn-SBA-15/KI catalyzed cycloaddition reaction, which were promising results to guide the catalyst design for CO2 conversion.

Catalytic coupling of carbon dioxide with epoxides to obtain cyclic carbonates is an important reaction that has been receiving renewed interest. In this contribution, the cycloaddition reaction in the presence of various hydrogen bond donors (HBDs) catalyzed by hydroxyl/carboxyl task-specific ionic liquids (ILs) is studied in detail. It was found that the activity of ILs could be significantly enhanced in the presence of ethylene glycol (EG), and EG/HEBimBr were the most efficient catalysts for the CO2 cycloaddition to propylene oxide. Moreover, the binary catalysts were also efficiently versatile for the CO2 cycloaddition to less active epoxides such as styrene oxide and cyclohexene oxide. Besides, the minimum energy paths for this hydrogen bond-promoted catalytic reaction were calculated using the density functional theory (DFT) method. The DFT results suggested that the ring-closing reaction was the rate-determining step in the HEBimBr-catalyzed cycloaddition reaction but the EG addition could remarkably reduce its energy barrier as the formation of a hydrogen bond between EG and the oxygen atom of epoxides led this process along the standard SN2 mechanism. As a result, the ring-opening reaction became the rate-determining step in the EG/HEBimBr-catalyzed cycloaddition reaction. The work reported herein helped the understanding and design of catalysts for efficient fixation of CO2 to epoxides via hydrogen bond activation.

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