Coupled Lewis Acid-base Synergetic Interface Of Cu/NC For CO₂ Fixation

Excessive emission of carbon dioxide has triggered numerous environmental problems,such as global warming,rising sea level,melting polar ice and so on.Efficient reuse of CO₂,which is an inexpensive,abundant and nontoxic gas,is consistently considered a promising green chemistry process.However,the high chemical stability of CO₂ makes its conversion difficult.Current strategies for chemical fixation of CO₂ mainly focus on the conversion of CO₂ into useful organic carbonates,carbamates,ureas and carboxylic acids.Cycloaddition of CO₂ to epoxides is an important method for the synthesis of cyclic carbonates,which are of great interest in industry as lithium battery electrolytes,nonprotic polar solvents and monomers used for generating polycarbonates.Recently,metal-organic frameworks（MOFs）and porous ionic polymers have been developed as reusable heterogeneous catalysts for the coupling reaction.This pioneering work has clearly demonstrated the importance of Lewis acid and/or base groups in facilitating the fixation of CO₂ and the activation of epoxides,even though the expensive and complex method for the synthesis of MOF materials will limit their practical applications.In principle,electron-rich and electron-deficient areas at the boundary of a Mott-Schottky heterojunction could also function as Lewis base and acid pairs,e.g.,in metal-semiconductor nanocomposites.Modification of the electron distribution within the metal-semiconductor nanocatalyst is an alternative and straightforward way to trigger a possible cycloaddition reaction without involving expensive ligands.The results are summarized as follows:（1）Two-dimensional carbon material with high surface area was synthesized by soft template method.The final catalyst Cu/NC material was synthesized with high-nitrogen doping and low-copper loading.With high surface area,high nitrogen content and low copper content,Cu/NC catalyst showed excellent performance on the coupling of CO₂ with styrene oxide into styrene carbonate under mild conditions.After optimization,the optimal catalytic conditions were determined.（2）It was confirmed that Cu played an important role as the electron donor to enhance the Lewis basicity of the carbon supports.Instead,the interfacial Schottky contact enabled the further enhancement in the acidity of the Cu species by introducing additional N heteroatoms to the carbon supports.The optimal Cu/NC-0.5 catalyst exhibited a remarkably high turnover frequency（TOF）value of 615 h^-1 at 80℃,which is 10 times higher than that of the state-of-the-art metal-based heterogeneous catalysts in the literature.