Research Of The Novel Metal-organic Frameworks Immobilied Tungsten Oxide Preparation And Its Catalytic Properties

Metal Organic Frameworks(MOFs) are porous crystalline materials which are self-assembled by linking organic ligands with metal ions or metal clusters to form infinite network structures. Due to their outstanding properties, MOFs have been extensively used in catalysis, gas storage, adsorption and separation, et al.In this paper, three different kinds of catalysts were prepared by traditional impregnation method and microwave-assisted synthesis method using Ui O-66 and MIL-101 as the supports, tungstic acid as the active precursor, and boric acid as the active assistant precursor. The catalytic performance of the as-prepared catalysts was investigated for the selective oxidation of cyclopentene(CPE) to glutaraldehyde(GA), using hydrogen peroxide as the oxidant and tert-butanol(TBA) as the solvent. Moreover, the catalysts were characterized by different techniques to further explore the relation between the catalytic performance and the physico-chemical structure of the catalysts. The main work of the paper is as follows:1. The novel heterogeneous WO3/Ui O-66 catalyst was prepared by traditional impregnation method and was systemically characterized by means of XRD, N2 adsorption, TG and FT-IR techniques. The results showed that CPE conversion and GA yield can reach 92.2% and 50.3%, respectively, using 40%(w) WO3/Ui O-66 as the catalyst at the conditions of n(CPE):n(H2O2):n(WO3) = 1:2.5:0.05, V(TBA):V(CPE)=10, reaction temperature = 35 ℃ and reaction time = 24 h. The characterization results illustrated MIL-101 has a high specific surface area, stable skeleton structures, and high load capacity of WO3. Heterogeneous and reusable experimental results showed that the catalyst was a true heterogeneous catalyst and has a good stability. Additionally, WO3 couldn’t be sufficiently activated and the interaction between WO3 and Ui O-66 was not strong because of Ui O-66 being not calcined at high temperature, which led to the lower catalytic performance and reusability of WO3/Ui O-66 catalyst.2. The novel heterogeneous B2O3-WO3/Ui O-66(MW) catalyst was prepared by the microwave-assisted synthesis method and was systemically characterized by different means of techniques. The results showed that CPE conversion and GA yield can reach 100% and 74%, respectively, using 15%(w)B2O3-40%(w) WO3/Ui O-66(MW) as catalyst at the conditions of n(CPE):n(H2O2):n(WO3):n(B2O3) = 1:2.5:0.05:0.065, V(TBA):V(CPE)=10, reaction temperature = 35 ℃ and reaction time = 24 h. All the characterization results showed that the special morphologies and crystalline structure of Ui O-66 could be well kept and its thermal stability was enhanced after WO3 and B2O3 species were introduced into Ui O-66, which were highly dispersed into the micropous cages of Ui O-66. The amount of low condensed oligomeric tungsten oxide species and W6+ species increased because of the interaction of B2O3 molecular and WO3 molecular. Moreover, CO-FT-IR adsorption experiments suggested that the novel moderate intensity of Lewis acid sites were formed upon incorporation of WO3 and B2O3 species into Ui O-66 which were beneficial to their good catalytic performance.3. The novel heterogeneous B2O3-WO3/MIL-101 catalyst was prepared by the microwave-assisted synthesis method and was systemically characterized by different means of techniques. The results showed that CPE conversion and GA yield can reach 100% and 76.1%, respectively, using 15%(w)B2O3-30%(w)WO3/ MIL-101 as catalyst at the conditions of n(CPE):n(H2O2):n(WO3):n(B2O3) = 1 : 2.5 : 0.05 : 0.065, V(TBA):V(CPE)=10, reaction temperature = 35 ℃ and reaction time = 24 h. All the characterization results showed that the special morphologies and crystalline structure of MIL-101 could be well kept and its thermal stability was enhanced after WO3 and B2O3 species were introduced into MIL-101, which were highly dispersed into the mesopous cages of MIL-101. The amount of W6+ species increased because of the interaction of B2O3 molecular and WO3 molecular. Moreover, CO-FT-IR adsorption experiments suggested that the novel moderate intensity of Lewis acid sites were formed upon incorporation of WO3 and B2O3 species into MIL-101 which were beneficial to their good catalytic performance.