Conversion of carbon dioxide (CO2) to value-added products is imperative to combat global warming. In this regard, herein we report a metal-free heterogeneous catalyst, boron-doped graphitic carbon nitride for effective conversion of CO2 to cyclic carbonates at atmospheric pressure under solvent-free conditions. The developed catalyst possesses acid-base dual functionality as active sites, which activate both epoxides as well as CO2 simultaneously to carry out the cycloaddition reaction. The catalyst showed a maximum yield up to 99 % with a turnover number of 173. Detailed optimization studies have been performed to find out the best doping content of boron and best conditions by varying the reaction time, temperature and catalysts amount. Furthermore, the ease of catalyst recovery and excellent recyclability demonstrate the sustainability and versatility of the catalyst for selective and efficient conversion of CO2 to cyclic carbonates at mild conditions.

Atmospheric pressure conversion of carbon dioxide to cyclic carbonates using a metal-free Lewis acid-base bifunctional heterogeneous catalyst

Synthesis and structural depiction of two new metal-organic frameworks (MOFs), namely, [{Zn(L)(oba)}·4H2O]α (Zn-MOF-1) and [{Cd1/2(L)1/2(nipa)1/2(H2O)1/2}·(DMF)1/2(H2O)]α (Cd-MOF-2) (where L = N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide, 4,4'-H2oba = 4,4'-oxybisbenzoic acid, and 5-H2nipa = 5-nitroisophthalic acid) are reported. Both Zn-MOF-1 and Cd-MOF-2 have been prepared by reacting ligand L and coligand 4,4'-H2oba or 5-H2nipa with the respective dihydrates of Zn(OAc)2 and Cd(OAc)2 (OAc = acetate). Crystal structure X-ray analysis discloses that Zn-MOF-1 displays an overall 2D → 3D interpenetrated framework structure. The topological analysis by ToposPro suggests a (4)-connected uninodal sql topology with a point symbol of {44·62} having 2D + 2D parallel polycatenation. However, crystal packing of Cd-MOF-2 adapted a porous framework architecture and was topologically simplified as (3,4)-connected binodal 2D net. In addition, both Zn-MOF-1 and Cd-MOF-2 were proved to be multifunctional materials for the recognition of organic amines and in the fixation of CO2 to cyclic carbonates. Remarkably, Zn-MOF-1 and Cd-MOF-2 showed very good fluorescence stability in aqueous media and have shown 98 and 97% quenching efficiencies, respectively, for 4-aminobenzoic acid (4-ABA), among all of the researched amines. The mechanistic study of organic amines recognition proposed that fluorescence quenching happened mainly through hydrogen-bonding and π-π stacking interactions. Additionally, cycloaddition of CO2 to epoxide in the presence of Zn-MOF-1 and Cd-MOF-2 afforded up to 96% of cyclic carbonate within 24 h. Both Zn-MOF-1 and Cd-MOF-2 exhibited recyclability for up to five cycles without noticing an appreciable loss in their sensing or catalytic efficiency.

Metal-Organic Framework-Based Selective Molecular Recognition of Organic Amines and Fixation of CO2 into Cyclic Carbonates.

The efficient conversion of carbon dioxide (CO2) to the valuable chemicals is of great significance but the development of robust catalyst is still an interesting and challenging issue. Four novel ionic liquids are facilely synthesized with the ability to adsorb carbon dioxide (CO2). [BZTMA+][−O2EEPZ+][Br−] and [DBUH+][−O2EEPZ+][Br−] could catalyze the cycloaddition of CO2 into cyclic carbonates under atmospheric pressure at 50 °C with 99.3 % and 97.5 % yields in the absence of co-catalyst and solvent. Moreover, the [DBUH+][−O2EEPZ+][Br−] could be reutilized by 11 times with a slightly decreased product yield. A new mechanism is proposed by the density functional theory (DFT). The excellent catalytic performance is mainly attributed to the ability of ionic liquids to adsorb CO2. After the CO2 is adsorbed, the formed intermediate would push the electrons towards the Br- anion leading to the stronger nucleophilic activation. This work introduces a new pathway to explore the ionic liquids for the chemical fixation of CO2.

“Responsive” ionic liquids to catalyze the transformation of carbon dioxide under atmospheric pressure

Selective Conversion of CO2 into Cyclic Carbonate on Atom Level Catalysts

Recent progress of catalysts for synthesis of cyclic carbonates from CO2 and epoxides

A series of rare-earth (RE) metal complexes (Y, Sm, Nd, and La) stabilized by polydentate N-methylethylenediamine-bridged tris(phenolato) ligands was synthesized and characterized. Lanthanum comple...

Haiwen Shan

Papers

Conversion of CO2 into Cyclic Carbonates under Ambient Conditions Catalyzed by Rare-Earth Metal Complexes Bearing Poly(phenolato) Ligand