多酸结构对纳米钛硅TS-1沸石催化氧化脱硫性能的影响

Effect of Polyoxometalate Structure on Catalytic Oxidative Desulfurization Performance of Nano Titanium Silicalite-1 Zeolite

采用浸渍法合成了纳米钛硅TS-1沸石负载的钼系列多金属氧酸盐(POM)复合催化剂,采用扫描电子显微镜(SEM)、傅里叶红外光谱(FT-IR)、固体紫外漫反射(UV-Vis)、X-ray粉末衍射(XRD)、氮气吸附脱附(BET)、^31P和^29Si魔角核磁共振(MAS-NMR)等对催化剂的结构进行表征。研究结果表明,在低温焙烧或烘干条件下,负载后催化剂多酸的结构保持,钼酸铵高温(550℃)焙烧后转变为三氧化钼。以有机硫化物噻吩(TH)、苯并噻吩(BT)和二苯并噻吩(DBT)的正辛烷溶液为模拟油品评价了催化剂的氧化脱硫性能。实验结果表明,纳米TS-1沸石载体上不同结构多酸作为脱硫催化剂对硫化物的脱除活性顺序为:Keggin型Mo-POM>Anderson型Mo-POM>Dawson型Mo-POM>Mo-金属氧化物。以上述负载的多酸为催化剂,在反应条件为:V(模拟油)=V(乙醇)=10.0 mL,m(催化剂)=0.2 g,n(H2O2)∶n(S)=10∶1,温度60℃,硫化物按照由易到难的脱除顺序为TH>DBT>BT,与常规的TS-1沸石或者多酸催化剂的脱除顺序存在明显差异。这是纳米TS-1沸石对于有机硫分子氧化反应的择形效应和POM催化氧化脱硫的电子云密度影响综合作用的结果。Keggin型Mo-POM催化剂具有良好的循环使用性能,是一类制备方法简单、催化活性高且稳定性好的绿色环保型催化剂。

Nano titanium silicalite-1(TS-1) zeolite catalysts loaded with a series of molybdenum-containing polyoxometalate(POM) were synthesized by the impregnation method. These catalysts were characterized by SEM, UV-vis, BET, XRD, 31P MAS-NMR and 29Si MAS-NMR spectroscopy. The characterization results show that the Keggin structure in the catalysts can be remained after calcination or drying under the low temperature, but ammonium molybdate changed into molybdenum trioxide after calcination at 550 ℃. A model of oil(n-octane solution of thiophene, benzothiophene and dibenzothiophene) was used to value catalytic oxidation desulfurization performance of these catalysts. It is found that the oxidative desulfurization efficiencies decrease in the order of Mo-POM(Keggin type)>Mo-POM(Anderson type)>Mo-POM(Dawson type)>molybdenum trioxide. When the reaction conditions are the model of V(simulated oil)=V(ethanol)=10.0 mL, m(catalyst)=0.2 g, n(H2O2)∶n(S)=10∶1, temperature=60 ℃, the desulfurization activity order of sulfur compounds is thiophene>dibenzothiophene>benzothiophene, which is obviously different from that of either TS-1 zeolite or POM. This may be derived from the synergy of the shape selectivity of nano-TS-1 zeolite and the electron cloud density of POM on the oxidation activity of organic sulfur molecules. Furthermore, the Keggin type Mo-POM-TS-1 catalysts show excellent recycling stability. All of which cause Mo-POM(Keggin type)-TS-1 catalysts to become a kind of environmental-friendly catalysts with simple preparation method, high catalytic activity and good stability.