Tungsten Coordination Structure in Tungsten-Silicon Zeolite and Its Catalytic Performance in Oxidative Cleavage of Methyl Oleate
W-Beta and W-MFI zeolites were prepared by post-synthesis and hydrothermal-synthesis methods,respectively.The coordination structures of tungsten in the zeolites and the ion species in the filtrate were characterized by XRD,low-temperature N2 adsorption-desorption experiments,UV-Vis and CSI-MS.Moreover,the activity and stability of the above W-based zeolites during the catalytic oxidative cleavage of methyl oleate were studied,and further correlated with the catalytic activity of the filtrate.The results reveal that in the W-MFI zeolite synthetized by hydrothermal method,the tetrahedral WO2(OSi)2 structure shows good stability;W-MFI possesses catalytic epoxidation activity,but without catalytic activity in the oxidative cracking of methyl oleate.In contrast,W-Beta zeolite prepared by the post synthesis method shows lower stability but higher catalytic activity in the oxidative cracking of methyl oleate due to the formation of WO3 nanoclusters as a result of the interaction between tungsten species and the silicone hydroxyl produced by dealumination.Peroxytungstate anion species with broad mass to charge ratio distribution,which were generated by the reaction of WO3 and H2O2 over the zeolite,show catalytic activity in the oxidative cracking of methyl oleate.
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