Synthesis, Characterization And Catalytic Properties Of MIL-100(Cr)Encapsulated Metal Salen Complexes

Transition metal complexes of Schiff-base exhibited excellent catalytic activity in a variety of chemical reactions and can mimic the active center of enzyme. But the Schiff base metal complexes prone to self-polymerization to form dimers or polymers to reduce the catalytic activity in the reaction process. The encapsulation of metal complexes into porous materials is an effective method to prevent the dimerization of complexes and to get a bionic catalyst which is similar to biological enzyme from structure and function, In the past, zeolites are the most commonly used support. In recent years, metal-organic frameworks(MOFs) were selected as the support to encapsulate metal Schiff-base complexes. Compared with the zeolites, MOFs possess larger specific surface area and richer topological structures. The advantages of these encapsulated complexes include high catalytic activity, easy separation of the product and reusability.In this paper, Cosalen was encapsulated in MIL-100(Cr) metal organic framework by "ship in a bottle" to synthesize a new catalyst, Cosalen@MIL-100(Cr). Its catalytic performance was tested by the oxidation of cyclohexane and electrochemical reduction of oxygen process. The main contents are as follows:The catalytic performance of Cosalen@MIL-100(Cr) was investigated via selective oxidation of cyclohexane in a solvent-free system with oxygen as the oxygen source. Reaction was carried out at130℃for6hours, Cosalen@MIL-100(Cr) exhibit significant catalytic performance:the KA-oil selectivity is above90%and the conversion of cyclohexane is above28%. In this reaction, MIL-100(Cr) plays two roles. As the carrier of encapsulated metal Schiff base complexes, MIL-100(Cr) prevented the polymerization of Schiff base metal complexes. At the same time, framework Cr ions are also effective catalytic sites for cyclohexane oxidation.Cosalen@MIL-100(Cr) modified glassy carbon electrode was prepared and studied on its electrocatalytic properties in the oxygen reduction reaction by electrochemical technology. The Cosalen@MIL-100(Cr) modified glassy carbon electrode exhibited a well-defined reduction peak at the potential of ca.-0.21V toward the oxygen reduction reaction. The catalytic effect is better than bare glassy carbon electrode. During the reaction, Cosalen play the role in accelerating the rate of oxygen diffusion. MIL-100(Cr) has a large surface area and pore volume, which is beneficial to increase the electroactive surface area of modified electrode. The results of cyclic voltammetry showed its electroactive surface area is nearly2times of the geometric surface area of bare GCE. Cosalen@MIL-100(Cr) shows the good electrocatalytic activity because of the synergistic effects of MOF and Cosalen in the cages of MIL-100(Cr). The reduction of O2on Cosalen@MIL-100(Cr) modified electrode involves4electron reduction pathway.