Synthesis And Performance Studies Of Polyoxometalate-based Metal-organic Framework Nanocrystalline Catalysts

Polyoxometalates（POMs）have strong Br?nsted acidity,reversible redox performance and stable structure,which make them have vigorous application prospects in the field of catalysis.Nevertheless,the dissolution of pure POMs in polar solvents makes POMs catalyst difficult to be recycled,and their agglomeration in non-polar solvents reduces the specific surface area of POM catalyst.Encapsulating POMs in metal-organic frameworks（MOFs）to obtain POMs-based metal-organic frameworks hybrids（POM@MOFs）is an effective strategy to solve the circulation and agglomeration problems of POMs catalyst,which has important scientific significance for the practical application of POMs catalyst.The main content and innovative work of this paper are as follows:1.The Keggin-type polyoxometalate H₅PMo₁₀V₂O₄₀（HPMo V）was encapsulated into Cu₃（BTC）₂ framework（H₃BTC=1,3,5-benzenetricarboxylic acid）via liquid-assisted grinding（LAG）method to obtain nanocrystalline POM@MOF,i.e.NENU-9N.A series of methods including powder X-ray diffraction（PXRD）,Fourier infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）,thermogravimetric analysis（TG）,nitrogen adsorption-desorption analysis were performed on the synthesized materials.The characterization results show that the prepared NENU-9N has good crystallinity,excellent thermal stability,permanent porosity and uniform particle size.The catalytic performance of NENU-9N for epoxidation of styrene with oxygen was studied,and the mechanism of NENU-9N catalyzed epoxidation of styrene was explored through free radical quenching experiments.Due to the synergistic catalytic effect between HPMo V and Cu^II,NENU-9N exhibits excellent catalytic performance.The conversion of styrene and the selectivity to styrene oxide can reach 97.2%and 93.5%,respectively.NENU-9N catalyzes the epoxidation of styrene with a high TOF value(156h^-1),which is one of the reported catalysts for the epoxidation of styrene with a high TOF value.2.The oxidative detoxification performance of NENU-9 to the sulfur mustard simulant（2-chloroethyl ethyl sulfide,CEES）was studied.Both oxygen and hydrogen peroxide can be used as oxidants to oxidize CEES.However,the peroxyacid produced in the oxygen/isobutyraldehyde oxidation system made the oxidation product of CEES was mainly toxic 2-chloroethyl ethyl sulfone（CEESO₂）.In the hydrogen peroxide system,NENU-9N as catalyst can completely convert CEES and produce non-toxic 2-chloroethyl ethyl sulfone（CEESO）with a selectivity>98%,indicating that NENU-9N can effectively purify mustard gas.