Preparation Of Keggin Type Heteropolyacids Supported On Mesoporous Millimeter Alumina Microspheres And The Study Of The Catalytic Performances

Heteropolyacids supported on mesoporous carriers with high specific surface area as a heterogeneous catalyst have been a research hotspot in the field of polyoxometalate catalysis. In this paper, the catalysts HPW-NH2-Al2O3 and HPW-NH2-C8-Al2O3 were successfully synthesized by immobilization of phosphotungstic acid H3PW12O40(HPW) on the surface of amino functionalized millimetre-sized mesoporous γ-Al2O3 beads, and the catalysts HPW@HKUST-1@Al2O3 and HSiW@HKUST-1@Al2O3 were successfully synthesized using hydrothermal method. The catalysts were characterized by FT-IR, XRD, BET, XRF, SEM, NH3-TPD and TG-DTA. The results demonstrate that the heteropolyacids are loaded on the carrier successfully and the catalysts keep their mesoporous structures. The catalytic performances of the above catalysts were also tested. The main results are described as follows:(1) Mesoporous γ-Al2O3 beads were functionalized using two kinds of silane coupling agents-trimethoxy(octyl)silane and (3-aminopropyl)triethoxysilane, and then HPW was loaded on the functionalized mesoporous γ-Al2O3 beads, the products were named as HPW-NH2-C8-Al2O3 and HPW-NH2-Al2O3. The acid catalytic activity of the two kinds catalysts were investigated by the hydrolysis reaction of ethyl acetate. The hydrolysis efficiencies were 4.45% and 8.27% respectively for HPW-NH2-C8-Al2O3 and HPW-NH2-Al2O3 using 0.2 g catalyst under 65℃ and the catalytic activities were 245.4 μmol·gacjd-1·min-1 and 182.0 μmol·gacid-1·min-1 respectively. The solubilization rates were 2.17% and 7.79% respectively for the first use and the catalytic efficiencies after 6 times reuse decreased 13.9% and 62.9% respectively. So catalyst HPW-NH2-C8-Al2O3 prosesses a super reuse ability than HPW-NH2-Al2O3, although the catalyst efficiency of HPW-NH2-Al2O3 is higher than HPW-NH2-C8-Al2O3 for the first use. The results show that the hydrophobic octyl groups formed on the surface of alumina have a protective effect on phosphotungstic acid and the catalyst HPW-NH2-C8-Al2O3 feature high specific surface area, mechanical strength and chemical stability as well as low cost.(2) The catalyst HPW-NH2-Al2O3 was successfully synthesized by immobilization of phosphotungstic acid H3PW12O40 (HPW) on the surface of amino functionalized millimetre-sized mesoporous γ-Al2O3 beads, through the electrostatic force of amino cation. The prepared HPW-NH2-Al2O3 beads exhibited excellent catalytic performance in the oxidative desulfurization of model oil composed of dibenzothiophene (DBT) and n-octane. Under optimal conditions,350 ppmws of sulfur content in 20 mL n-octane can be dropped down to 2.8 ppmws in 2 hours using 60 mg HPW-NH2-Al2O3 catalyst. The catalyst can be conveniently recycled by simple decantation method. After 5 times recycling, the oxidation desulfurization efficiency only dropped down from 99.2% to 98.6%. The results indicate that HPW-NH2-Al2O3 beads can be the excellent catalysts for oxidative desulfurization and can be reused without noticeable efficiency loss.(3) HKUST-1 and heteropolyacids (HPAs) were highly dispersed on the millimetre-sized mesoporous γ-Al2O3 beads through hydrothermal method and two kinds of catalysts HPW@HKUST-1@Al2O3 and HSiW@HKUST-1@Al2O3 were prepared. The complexes are used as the acid catalysts for the synthesis of ethyl acetate and n-butyl acetate, the results show that the catalytic selectivety are 100% for both of the ester synthesizes. For the ethyl acetate synthesis the catalytic efficiency of HPW@HKUST-1@Al2O3 is 92.3% and the catalytic efficiency of HSiW@HKUST-1@Al2O3 is 95.1% using 0.4 g catalyst under 75℃ when the molar ratio of acid to alcohol is 2; for the butyl acetate synthesis the catalytic efficiency of HPW@HKUST-1@Al2O3 is 82.7% and the catalytic efficiency of HSiW@HKUST-1@Al2O3 is 84.9% using 0.4 g catalyst under 110℃ when the molar ratio of acid to alcohol is 2. The results show that the catalyst activity of HSiW@HKUST-1@Al2O3 is higher than HPW@HKUST-1@Al2O3. The catalysts were used repeatedly for 6 times and showed no significant efficiency loss. The mechanical strength of the catalysts increased 60.0% and 57.9% respectively for HPW@HKUST-1@Al2O3 and HSiW@HKUST-1@Al2O3 compared to the barely γ-Al2O3 , which illustrates that the γ-Al2O3 plays a role to stabilize HKUST-1 and HP As structure as well as the carrier, thus prevents its destruction.