Synthesis And Desulfurization Performance Of Polyoxometalates-based TiO₂ Low-dimensional Nanomaterials

Sulfur oxides?SOx?,which were emitted by combusting sulfur-containing fuel,have seriously affected the health of human and developments of social.In order to reduce the emission of SOx,it is urgent to explore catalysts for deep desulfurization to decrease sulfur concentration in fuels.Polyoxometalates?POMs?have been widely studied due to their unique structures and properties.Many environmental problems have been solved using polyoxometalates.However,POMs homogeneous catalysts are not easy to be reused,and restrict its applications.Heterogeneous catalysts forming by loading POMs on solid substrates are good strategies for solving this problem.TiO₂ has been proved excellent desulfurization performance in oxidation desulfurization system.Therefore,POMs loading on TiO₂ will achieve good desulfurization effect.Electrospinning is a simple and effective method to fabricate low-dimension nanomaterials.To date,it has not been reported that POMs-loading TiO₂ nanomaterials are prepared by electrospinning.Hence,it is an important and meaningful subject of study to fabricate POMs-loading TiO₂ nanomaterials by electrospinning and to investigate their desulfurization performance.In this dissertation,Keggin-type POMs and transition metals substituted Keggin-type POMs have been evenly distributed on TiO₂ nanofibers.These catalysts applicating in extraction catalysis oxidation desulfurization system?ECODS?can achieve the purpose of deep desulfurization.1.PW12/TiO₂ nanofibers have been successfully prepared via calcinating off the respective electrospun PVP/[PW12 + Ti?OC4H9?4] composite nanofibers for the first time.PW12/TiO₂ nanofibers were composed of Keggin-type PW12 and anatase phase TiO₂.The diameter of PW12/TiO₂ nanofibers was approximately 100 nm.DBT can be completely removed within 30 min using 0.02 g 40 wt.% PW12/TiO₂ nanofibers as catalysts at70?C and O/S molar ratio 8:1.Compared with 40 wt.% PW12/TiO₂ nanoparticles,40 wt.% PW12/TiO₂ nanofibers exhibit higher desulfurization efficiency at the same condition,because that nanofibers with large surface area can absorb more DBT.In addition,40 wt.% PW12/TiO₂ nanofibers also can efficiently remove BT and 4,6-DMDBT.After 5-times recycling,the result of deep desulfurization was reached for 40 wt.% PW12/TiO₂ nanofibers.Therefore,these novel PW12/TiO₂ nanofibers have potential industrial application.2.PW11Sn/TiO₂?PW11Sn =?OTA?3PW11SnO39,OTA = octadecyl trimethyl ammonium?nanofibers have been successfully prepared via combining with electrospinning and hydrothermal method,and the diameter was about 98 nm.The crystal phase of TiO₂ wasinfluenced by loading of PW11 Sn,and the crystal phases of samples could be tuned by various loading amount of PW11 Sn.The desulfurization efficiency was influenced by the crystal phase,morphology and synthesis method of catalysts.The optimum desulfurization conditions in ECODS was obtained as following: O/S mole ratio value was 6:1 and reaction temperature was at 60 °C,the DBT conversion efficiency can achieve 100% within 20 min using 0.02 g 50 wt.% PW11 Sn /TiO₂ nanofibres as catalysts.Even after at least 7-times recycling,the catalytic activity of 50 wt.% PW11 Sn /TiO₂ nanofibres was not significant decreased.Additionally,50 wt.% PW11Sn/TiO₂ nanofibers also can efficiently remove BT and 4,6-DMDBT.3.?HTA?5SiW9Co3O39/TiO₂ nanofibers have been prepared via electrospinning combined with hydrothermal method.The crystalline phase of TiO₂ was influenced by loading POMs.Compared with Si W9Co3/TiO₂ nanofibers,5 wt.% Si W9Co3/TiO₂ nanoparticles exhibited the higher catalytic activity,96% DBT could be converted within 120 min under the conditions of catalyst dosage 0.02 g at 70 °C and O/S value was 8:1.This is because that the surface area of TiO₂ nanofibers decreased after loading POMs,and the amount of DBT absorbed on samples reduced.For different substrates,the desulfurization efficiencies decreased in the following orders: DBT > 4,6-DMDBT > BT under the same conditions.In addition,the possible desulfurization mechanism of?HTA?5SiW9Co3O39/TiO₂ nanomaterials were also studied.4.A series of amphiphilic Ti-peroxide-containing POMs C[PWy?TiO₂?zO38]?C = DTA,CTA,STA;y = 9,10,11;z = 3,2,1?were obtained via ions exchange method.These catalysts were applicated in ECODS and the results indicated that amony these catalysts,C12PW10?TiO₂?2 showed fast and ultra-deep desulfurization performance: DBT can be completely removed within 10 min using 0.01 g catalysts at 70 °C.Moreover,x wt.%PW10?TiO₂?2/TiO₂?x = 10,28,38 and 50?nanofibers have been prepared via electrospinning combined with hydrothermal method.The crystal phase of TiO₂ was influenced by loading of PW10?TiO₂?2,and the crystal phases of samples could be tuned by various loading amount of PW10?TiO₂?2.Among these nanofibers catalysts,28 wt.% PW10?TiO₂?2/TiO₂ show excellent desulfurization performance,and they have potential application in industrial desulfurization.