A new approach to tailoring edge active groups of graphitic carbon nitrides for catalytic conversion of CO2 into cyclic carbonates was proposed in this work. To improve the catalytic performance, boron-doped melamine-derived graphitic carbon nitrides (MCNB) with numerous exposed edge defects were prepared by using 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) as the soft template and boron source. Different mass ratios of BmimBF4 to melamine were explored for MCNB preparation, MCNB(x) (x is the mass ratio) with different polymerization degree, pore structure and boron doping content were obtained, and the relationship between MCNB properties and the corresponding catalytic activity was then investigated. With low polymerization degree, abundant meso-macroporous structure and small amounts of boron (<1.59 atm%) doped in the skeleton, MCNB(0.01) exhibited better catalytic performance and could be suitable for various epoxide substrates with the yield of cyclic carbonates up to 89.0% at 130 °C in 6 h. According to the XPS analysis and DFT calculation results, the active centers were confirmed to be the partially-condensed amino groups in edge defects, which were enhanced by moderate doping of boron in the skeleton.

In order to overcome existing solid catalysts' disadvantages of low stability and activity, urea-derived graphitic carbon nitrides (u-g-C3N4) with higher stabilities and more active centers were prepared under different temperatures (550–450 °C). With a decrease in preparation temperature from 550 °C to 480 °C, a u-g-C3N4 of lower crystallinity with a smaller polymerization degree was obtained and found to have a higher catalytic activity for CO2 conversion into propylene carbonate. The higher activity of the u-g-C3N4 caused by decreasing the temperature might be ascribed to the lower crystallinity and polymerization degree, which led to more edge defects, wherein the incompletely-coordinated nitrogen atoms served as the main active sites in the cycloaddition reaction. Among all the prepared catalysts, that prepared at 480 °C (u-g-C3N4-480) showed the highest catalytic activity for CO2 conversion and exhibited great suitability for other epoxide substrates.

A series of hydroxyl-functionalized poly(ionic liquids) (PILs) were synthesized and employed as catalysts for the synthesis of cyclic carbonates from CO2 and epoxides without the use of any co-catalyst or organic solvent. It was demonstrated that hydroxyl and bromide anion had an excellent synergetic effect on promoting the reaction, and the PILs catalysed co-polymerization of 1-vinyl-3-carboxyethylimidazolium bromide with the cross-linker divinylbenzene (DVB) was observed to be the most efficient, with nearly a 99% yield of propylene carbonate and 100% selectivity. The effects of temperature, pressure and reaction time on the reaction were also investigated. Moreover, the catalysts can be easily recovered and reused more than five times with only a slight decline in catalytic activity. This process carries huge industrial applications due to the reactions high efficiency and the ease of catalyst separation and recycling, which could be profitably applied to the development of fixed-bed continuous flow reactors.

Polystyrene-bound diethanolamine based ionic liquids (PS-DHEEAB and PS-THEAB) were synthesized and applied for the chemical fixation of CO2 into cyclic carbonates without any additional co-catalyst and solvent. The effect of the catalysts with different number of hydroxyl group in the cation of the IL on the reaction was systematically investigated. Highest activity and selectivity were achieved in the presence of polystyrene supported diethanolamine ethyl bromide (PS-DHEEAB) in comparison with other catalysts employed. The catalyst was tough in stability and also found to be extended to a variety of terminal epoxides and aziridines. The relationship between high catalytic reactivity and the –OH functional groups was proposed.

We systematically screened binary catalysts for synthesis of dimethyl carbonate (DMC) from CO2, CH3OH and ethylene oxide (EO) in the presence of H2O by two-step transesterification process, and found the commercial quaternary ammonium salts/K2CO3, pyridinium salts/K2CO3 and KI/K2CO3 were effective binary catalysts for two-step synthesis of DMC with no need for separation of ethylene carbonate (EC). Near 100% conversion of EO and 82% yield of DMC were obtained under mild reaction conditions. However, the imidazolium salts were not compatible with inorganic alkaline possibly because of the reactive C(2)–H in the imidazolium ring. Furthermore, the KI/K2CO3 could be easily recovered and reused 12 times without obvious loss of its catalytic activity. The process avoids EC separation, and represents a simple, ecologically safer, cost-effective and energy-saving route for synthesis of DMC with high product quality, as well as easy catalyst recycling.

We compared the efficacies of urea + hydrogen peroxide (U+HP) and hydrogen peroxide (HP) as an oxidizing agent in the epoxidation of propylene catalyzed by a titanium silicate-1 (TS-1) molecular sieve. The TS-1 catalyst exhibited good performance and stability in the TS-1/(U+HP) system. EPR results showed that more active Ti-superoxo species led to better performance of TS-1 in the TS-1/(U+HP) system than in the TS-1/HP system.

In order to overcome existing solid catalysts' disadvantages of low stability and activity, urea-derived graphitic carbon nitrides (u-g-C3N4) with higher stabilities and more active centers were prepared under different temperatures (550–450 °C). With a decrease in preparation temperature from 550 °C to 480 °C, a u-g-C3N4 of lower crystallinity with a smaller polymerization degree was obtained and found to have a higher catalytic activity for CO2 conversion into propylene carbonate. The higher activity of the u-g-C3N4 caused by decreasing the temperature might be ascribed to the lower crystallinity and polymerization degree, which led to more edge defects, wherein the incompletely-coordinated nitrogen atoms served as the main active sites in the cycloaddition reaction. Among all the prepared catalysts, that prepared at 480 °C (u-g-C3N4-480) showed the highest catalytic activity for CO2 conversion and exhibited great suitability for other epoxide substrates.