The cycloaddition of epoxides and carbon dioxide represents a straightforward and atom-efficient method for synthesis of cyclic carbonates and utilization of CO2. So far, homogeneous metal complexes have been mainly a...The cycloaddition of epoxides and carbon dioxide represents a straightforward and atom-efficient method for synthesis of cyclic carbonates and utilization of CO2. So far, homogeneous metal complexes have been mainly applied for such transformations. Here, we describe the synthesis of novel heterogeneous Zn-based catalysts, which were conveniently prepared by pyrolysis of an active- carbon-supported phenanthroline-ligated Zn(OAc)2 complex. Detail structural characterizations proved the existence of single zinc sites in the active material. Compared to a Zn-based nanoparticle (Zn-NP) catalyst, the resulting single metal atom catalyst (SAC) displayed improved activity and stability for the cycloaddition of epoxides. By applying the optimal catalyst, a variety of carbonates were successfully obtained in high yields with good functional group tolerance.展开更多
The development of heterogeneous catalysts with well-defined uniform isolated or multiple active sites is of great importance for understanding catalytic performances and studying reaction mechanisms.Herein,we present...The development of heterogeneous catalysts with well-defined uniform isolated or multiple active sites is of great importance for understanding catalytic performances and studying reaction mechanisms.Herein,we present a CoCu dual-atom catalyst(CoCu-DAC)where bonded Co-Cu dual-atom sites are embedded in N-doped carbon matrix with a well-defined Co(OH)CuN_(6)structure.The CoCu-DAC exhibits higher catalytic activity and selectivity than the Co single-atom catalyst(Co-SAC)and Cu single-atom catalyst(CuSAC)counterparts in the catalytic oxidative esterification of alcohols and a variety of methyl and alkyl esters have been successfully synthesized.Kinetic studies reveal that the activation energy(29.7 kJ mol^(-1))over CoCu-DAC is much lower than that over Co-SAC(38.4 kJ mol^(-1))and density functional theory(DFT)studies disclose that two different mechanisms are regulated over CoCu-DAC and Co-SAC/Cu-SAC in three-step esterification of alcohols.The bonded Co-Cu and adjacent N species efficiently catalyze the elementary reactions of alcohol dehydrogenation,O2activation and ester formation,respectively.The stepwise alkoxy pathway(O-H and C-H scissions)is preferred for both alcohol dehydrogenation and ester formation over CoCu-DAC,while the progressive hydroxylalkyl pathway(C-H and O-H scissions)for alcohol dehydrogenation and simultaneous hemiacetal dehydrogenation are favored over Co-SAC and Cu-SAC.Characteristic peaks in the Fourier transform infrared spectroscopy analysis may confirm the formation of the metal-C intermediate and the hydroxylalkyl pathway over Co-SAC.展开更多
基金supported by the National Key R&D Program of China(2017YFA0403103)the state of Mecklenburg-Vorpommern and the Bundesministerium für Bildung und Forschung~~
文摘The cycloaddition of epoxides and carbon dioxide represents a straightforward and atom-efficient method for synthesis of cyclic carbonates and utilization of CO2. So far, homogeneous metal complexes have been mainly applied for such transformations. Here, we describe the synthesis of novel heterogeneous Zn-based catalysts, which were conveniently prepared by pyrolysis of an active- carbon-supported phenanthroline-ligated Zn(OAc)2 complex. Detail structural characterizations proved the existence of single zinc sites in the active material. Compared to a Zn-based nanoparticle (Zn-NP) catalyst, the resulting single metal atom catalyst (SAC) displayed improved activity and stability for the cycloaddition of epoxides. By applying the optimal catalyst, a variety of carbonates were successfully obtained in high yields with good functional group tolerance.
基金supported by the National Natural Science Foundation of China(22372180 and 22202216)the Natural Science Foundation of Gansu Province and the Major Project of Gansu Province(21JR7RA096 and 21ZD4WA021)+2 种基金the Youth Innovation Promotion Association(2023441)Lanzhou Institute of Chemical Physics(LICP)Cooperation Foundation for Young Scholars(HZJJ21-06)Key Program of the Lanzhou Institute of Chemical Physics(KJZLZD-2)。
文摘The development of heterogeneous catalysts with well-defined uniform isolated or multiple active sites is of great importance for understanding catalytic performances and studying reaction mechanisms.Herein,we present a CoCu dual-atom catalyst(CoCu-DAC)where bonded Co-Cu dual-atom sites are embedded in N-doped carbon matrix with a well-defined Co(OH)CuN_(6)structure.The CoCu-DAC exhibits higher catalytic activity and selectivity than the Co single-atom catalyst(Co-SAC)and Cu single-atom catalyst(CuSAC)counterparts in the catalytic oxidative esterification of alcohols and a variety of methyl and alkyl esters have been successfully synthesized.Kinetic studies reveal that the activation energy(29.7 kJ mol^(-1))over CoCu-DAC is much lower than that over Co-SAC(38.4 kJ mol^(-1))and density functional theory(DFT)studies disclose that two different mechanisms are regulated over CoCu-DAC and Co-SAC/Cu-SAC in three-step esterification of alcohols.The bonded Co-Cu and adjacent N species efficiently catalyze the elementary reactions of alcohol dehydrogenation,O2activation and ester formation,respectively.The stepwise alkoxy pathway(O-H and C-H scissions)is preferred for both alcohol dehydrogenation and ester formation over CoCu-DAC,while the progressive hydroxylalkyl pathway(C-H and O-H scissions)for alcohol dehydrogenation and simultaneous hemiacetal dehydrogenation are favored over Co-SAC and Cu-SAC.Characteristic peaks in the Fourier transform infrared spectroscopy analysis may confirm the formation of the metal-C intermediate and the hydroxylalkyl pathway over Co-SAC.
