| WO3/ZrO2 type solid superacids,have attracted much attention recently,because they are noncorrosive,environmentally friendly and reusable at high temperatures. The typical feature of these solid superacids is highly acidic and stabile.Compared with those traditional solid acid catalysts,they make up the deficiency in acid strength, meet the requirement for the strong acid-catalyzed reactions and catalyze the reaction at relatively low temperatures.As a result,energy can be saved and side reactions are decreased.Compared with SO42-/ZrO2 type solid superacids,despite of a bit weaker acid strength,they present much better stability in H2,O2 and H2O atmosphere during the heterogeneous catalysis.Therefore,they are recognized as a kind of novel catalytic materials which are green and have potential applications.Recently,with the increasing of environmental constrains,the environmentally unfriendly catalysts used in petrochemical industry,such as HF,H2SO4,H3PO4 and AlCl3,are urgent to be substituted by new clean catalysts.WO3/ZrO2 type solid superacids are non-halogen,environmentally friendly,simply-sythesized,incorrosive, strong acidic,thermalstable and reusable.They are possible to become the substitute of those environmentally unfriendly catalysts,and thus a number of environmentally friendly processes may be established.In the present study,we focus on the effects of synthesis methods and the secondory promoter on the structure and catalytic behavior of WO3/ZrO2 catalysts onα-pinene isomerization and n-heptan hydroisomerization.In the third chapter of this thesis,impregnation,refluxing impregnation and coprecipitation methods were used to synthesize the WO3/ZrO2 catalysts.The hydrothermal treatment can stabilize the tetragonal phase of ZrO2 and prevent the growth of ZrO2 crystallites.Comparing three series of catalysts,samples prepared by refluxing impregnation exhibited the best activity forα-pinene isomerization which is probably due to the relatively large surface area and more acid sites.The most active sample is IH-18WZ with the isomerization conversion of 76.2%and selectivities to camphene and limonene of 85.8%at 90℃after 5 h on stream.The conversion ofα-pinene kept at 68.6%after 3 times of recycles,which shows a good reusability. Moreover,the selective poisoning experiment and the pyridine-absorbed IR showed that Brφnsted acid sites apparently contribute most of the activity and the weak Brφnsted acid sites should be active for theα-pinene isomerization.In the forth chapter of this thesis,Ga2O3 was doped in the Pt/WO3/ZrO2 catalysts through coprecipitation method.Incorporation of small amounts of Ga2O3 into Pt/WZ increases the activity substantially and improves the isomerization selectivity to some extent.The isomerization activity achieved the highest value on Pt/WO3/Ga2O3-ZrO2 catalyst when the WO3 concentration is 15 wt%,the Ga/Zr atom ratio is 0.02 and the calcination temperature is 800℃.When it undergos reaction at 200℃with the WHSV at 0.9 h-1,the catalyst exhibits a constant n-heptane hydroisomerization performance with high n-C7 conversion(76.7%) and C7 isomer selectivity(93.9%) for at least 80 h,which shows good prospects for industrial applications.The promoting role of Ga2O3 may be attributed to an enhancement of Brφnsted acidity, variation in the ratio of Brφnsted acidity to Lewis acidity and increased H storage capacity. |
