Modulating the Acidic and Basic Site Concentration of Metal-Organic Framework Derivatives to Promote the Carbon Dioxide Epoxidation Reaction.

Metal-organic framework (MOF) is an ideal precursor/template for porous carbon, and its active components are uniformly doped, which can be used in energy storage and catalytic conversion fields. Metal-organic framework PCN-224 with carboxylporphyrin as the ligand was synthesized, and then Zn and Co ions were coordinated in the center of the porphyrin ring by post-modification. Here, PCN-224-ZnCo with different ratios of bimetallic Zn /Co ions were used as the precursor, and the metal-nitrogen-carbon(M-N-C) material of PCN-224-ZnCo-950 was obtained by pyrolyzing the precursor at 950 °C in Ar. Because Zn is easy to volatilize at 950 °C, the formed M-N-C materials can reflect different Co contents and different basic site concentrations. The formed material still maintains the original basic framework. With the increase of Zn /Co ratio in precursor, the concentration of N-containing alkaline sites in pyrolysis products gradually increase. Compared with the precursor, PCN-224-ZnCo -950 with Zn /Co =1 : 1 has greatly improved basicity and suitable acidic/ alkaline site concentration. It can be efficiently used to carbon dioxide absorption and catalyze the cycloaddition of CO with epoxide. More importantly, the current method of adjusting the acidic/basic sites in M-N-C materials through volatilization of volatile metals can provide an effective strategy for adjusting the catalysis of MOF derivatives with porphyrin structure.