Design Of Hybrid Catalysts Based On Schiff Base Complexes And Their Oxidation Catalytic Behaviors

The heterogeneous catalysis has received more and more attentions in recent years, and heterogeneous oxidation catalysis is one of the more important research fields. Among the many catalysts, polyoxometalates (POM) and metal-salen (N,N-bis(salicylidine)ethylenediamine) complexes have already been important oxidation catalysts, which are major oxidation catalysts for oxidation (epoxidation) of styrene and other olefin. Although the homogeneous POM and salen-metal catalysts have high activity and selectivity, there are also some shortcomings, such as easy to break down, difficult to recycle. The catalytic performance can be greatly improved through the immobilization, and it's an effective way to achieve their application.In this dissertation, the mesoporous composite catalysts based on transition metal-monosubstituted Keggin-type polyoxometalates and entrapped dimeric Mn(salen) complexes have been prepared, which were further modified with organic silanes (aminepropyltrimethoxysilane or phenyltrimethoxysilane). To evaluate the catalytic performance of the resulting materials, selective oxidation of styrene and olefin epoxidation are picked out to be a model reaction, respectively. Specific contents are as follows:1. In this paper, a series of ordered mesoporous composite materials K10-nXn+MW11O39-Schiff-SBA-15(X = P/Si, M = Co/Ni/Cu/Mn) have been prepared via postsynthetic grafting for oxidation catalytic reaction. The composite materials were well characterized by spectroscopy methods, X-ray diffraction analysis, transmission electron microscopy, and nitrogen sorption analysis. The results confirm the structure integrities of the Keggin unit and Schiff base ligand after the incorporation. The products had highly ordered mesoporous structure. Compared with the Keggin unit, the BET surface area of the composite materials was greatly imoroved. In the composite materials, The Keggin unit and the silica modified Schiff base were firmLy combined by the M-N coordinate bond formed via the coordination of transition metal center in the SiW11M cluster with the nitrogen atoms of imine surface groups in Schiff-SBA-15 silica material.These materials were subsequently utilized as efficient and selective catalysts in the reaction of oxidation of styrene to benzaldehyde using H2O2 as an oxidant. The influences of key reaction parameters, including the molar ratios of H2O2 to styrene, compositions and loadings of the neat mono-TMSPs, solvents, the catalyst amount, and reaction temperatures on the reactivity and selectivity, were also studied. Finally, the reusability of the catalysts was evaluated. 2. In this study, a series of robust and reusable diamine-bridged dimeric Mn(salen) complexes were prepared firstly by the modified ship in a bottle strategy(SIB). A simple and effective methodology for the immobilization of monomeric and dimeric Mn(salen) complexes was developed in our current work. The hybrid materials were well characterized by spectroscopy methods, X-ray diffraction analysis, transmission electron microscopy, and nitrogen sorption analysis. The results confirmed the basic structure of the Mn(salen) complexe did not change. The immobilized dimeric Mn(salen) complexes exhibited a 3D cage-like periodic mesostructure. Compared with homogeneous catalyst, the hybrid catalysts are easy separation and recycling. In the hybrid catalyst, the dimeric Mn(salen) complexes are in the form of non-covalently encapsulated within the nanocages of periodic mesoporous organosilica.These materials were subsequently utilized as efficient and selective catalysts in the reaction of epoxidation of olefins to epoxide using NaClO as an oxidant. The influences of key reaction parameters, including solvents, the molar ratios of NaClO to olefins, compositions and loadings of the neat Mn(salen), the catalyst amount, and reaction temperatures on the reactivity and selectivity, were also studied. Finally, the reusability of the catalysts was evaluated.