Cucurbiturils:Synthesis And Applications In CO₂ Adsorption And Catalytic Conversion To 2-imidazolidone

The rapid development of industrial civilization has led to severe environmental problems,for example,the global warming problem.CO₂ storage and transformation are of significant for its negative effect on climate change.In recent years,the new application of supermolecules in gas capture and selective separation is becoming attractive.Macrocyclic supramolecular compounds can not only adsorb CO₂ but also improve its chemical conversion due to their unique cavity structure and molecular recognition capability.Unlike other macrocyclic supramolecular compounds such as crown ethers,cyclodextrins and calixarene,few study reported the application of cucurbituril family in CO₂ adsorption and chemical conversion.Following the reported ways in literature,a series of cucurbiturils were synthesized by the one-step syhthesis and purification method.The products were characterized by element analyzer,differential scanning calorimeter and nuclear magnetic resonance spectrometer for confirming the products of cucurbit[6]uril,cucurbit[7]uril,and cucurbit[8]uril.The high-pressure quartz spring method was employed to study the adsorption of CO₂ by using the as-synthesized cucurbituril compounds.Results showed that the amount of CO₂ adsorption of cucurbit[6]uril was better than those of cucurbit[7]uril and cucurbit[8]uril.The adsorption of cucurbit[6]uril to CO₂ reached 0.345 g/g at 298.2 K and 5.0 MPa,revealing a potential CO₂ adsorbent.Therefore,the isothermal adsorption curves of cucurbit[6]uril to C2 were obtained at 298.2 K,303.2 K,308.2 K and 313.2 K.Results showed that cucurbit[6]uril has good CO₂ adsorption from 0.1 to 8.0 MPa.It also exhibited better selectivity for CO₂ over CO and H2.The CO₂ cyclic adsorption-desorption study showed that cucurbit[6]uril had good stability and regeneration.From the pressure swing adsorption device when using cucurbit[6]uril as the adsorbent at 8.0 MPa,it was found that CO₂ concentration in the H2/CO/CO₂ mixture was greatly reduced and almost 100%syngas?H2+CO?could be achieved after the adsorption column,indicating potential role of cucurbit[6]uril in CO₂ separation.CeO₂ was prepared for activation of CO₂,and then the bifunctional composite catalyst,cucurbit[6]uril@CeO2 which bears both adsorption and catalytic activity,was prepared.It was applied to the catalytic conversion of ethylenediamine and CO₂ to 2-imidazolidone.It demonstrated that the molar ratio of CeO₂ to cucurbit[6]uril had significant effect on the catalytic activity,and the catalyst CBCe-8-250C showed the best catalytic activity?both the conversion and selectivity were close to 100%?with good reuse performance,which is superior to the catalysts reported in the literature.