Preparation And Properties Study Of Polyoxometalate-based Heterogeneous Catalyst

Polyoxometalates (POMs) are a large group of anionic metal oxides of V, Mo, W and Nb etc. in their highest state. In comparison with organic complex, POMs possess excellent thermal stability and oxidation stability. POMs have many unique properties, such as redox, acidity, fast electron transfer and solubility, which endows POMs with outstanding catalytic activity and broad application in the field of catarysis. To realized the application of POMs-based catalyst to the industrial production, the heterogenization of pure POMs has been the primary target in the development POMs catarysis. At present, two strategies have attracted lots of interest, that is immobilization and solidification of POMs. One of the effective strategies that can achieve the aim of the immobilization of POMs is to intercalate POMs anions into the gallery of the layered double hydroxides (LDHs). The composite material of POMs-intercalated LDHs (POMs-LDHs) own a variety of properties, including the host-guest interaction, the confinement effect in the gallery of LDHs and the synergetic effect between LDHs layer and the POMs anions. As a result, POMs-LDHs as a heterogeneous catalyst have been applied to the synthesis of organic fine chemicals, oxidative desulfurization of oil and degradation of organic pollutants in the waste water, etc. The traditional synthesis methods of preparation of POMs-LDHs material including co-precipitation, calcination-rehydration and ion exchange, etc. These methods have some drawbacks in intercalating large size POMs anions into the gallery of LDHs, such as Dawson POMs anions. Besides, the intercalation of POMs anions into LDHs can not be achieved in the air condition (with the existence of CO32-). Thus the condition of the preparation is very harsh and the synthesis process is last a long time. To solve these problem, it is required to develop some new methods for preparation of POMs-LDHs.1. By using organic anions pillaring method, we intercalated Dawson POMs anions into the gallery of Mg3Al-LDHs and fully study the structure and catalytic properties of the as-prepared POMs-LDHs. The detailed works is as follow. Through two times ion exchange, a series of different transition metal-substituted Dawson POMs anions were intercalated into the gallery of Mg3Al-LDHs and composite materials of Mg3Al-P2W17X were obtained (X= Mn, Fe, Co, Ni, Cu and Zn). The catalyst Mg3Al-P2Wi7Zn was applied to the sulfoxidation of various sulfides, which can be easily separated and recovered. The catalyst shows high catalytic activity and selectivity, especially the selectivity can up to 99%.2. By using Tris to modification of the layer of LDHs, the strong interaction between the host layer and POMs anions was weakened to a lot, so that we can intercalate POMs anions into the gallery of LDHs under the condition of air. By using this method, we have successfully prepared a new POMs-LDHs of Tris-LDH-La(PW11)2. Application of as a heterogeneous catalyst to N-oxidation of pyridines-based derivatives shows high efficiency and easy separation of the catalyst. Moreover, the catalyst can also achieve 99% deep denitrogenation of the model oil.