Synthesis And Characterization Of Keggin-type Double Cobalt Polyoxometalate/amino Modified SBA-15 Hybrid Material

Polyoxometalates(POMs)have been widely used as catalyst which has an excellent performance.At catalytic reactiori,It was often used in acid catalytic,oxidative catalytic and photocatalytic reaction.Due to having relatively good acid and oxidative catalytic performance,POMs containing Co have been applied in catalysis,such as oxidation of benzyl alcohol,and olefins,acetals reaction.However,POM directly used in catalysis can be soluble polar solvent such as water,and after the completion of the reaction catalyzed,POM can not been easily recycled.In the present situation,it caused the high cost and the product was too difficult to separate.And insoluble POM which has small specific surface area of the sample had low catalytic activity.So here we used SBA-15 which have high specific surface area as a carrier-supported to load POM,so as to solve the difficulties of POM sample recovery and the problems of small specific surface area.The common method which loaded POM to carrier was impregnation method,and hybrid material obtained in this method relys on physical force make POM adsorbed on the surface of the carrier,and because a more solid chemical force between the carrier and POM was not fomied,the POM loaded at carrier was easily eluted and lost at the catalytic reaction process.At here we used the APTES grafting SBA-15 aminopropyl into the bore,thereby obtaining amino-modified NH2-SBA-15,and then through the second grafting,anchor POM to NH2-SBA-I5 within the channel,thereby obtaining POM/NH2-SBA-15 mesoporous hybrid materials,make POM solid load in the carrier chamnel,we investigated the effect of synthesis conditions on the composition and structure of hybrid materials,and investigated which way to load.1.Synthesis and characterization of Co-containing polyoxometalateWe used Na2WO4 and Co(OAc)2 as raw materials in an aqueous solution with glacial acetic acid to adjust pH,and then synthesized several polyoxometalates:K7Co?W11Co?(H2O)O39,K8Co?W11Co?(H2O)O39,K6Co?W12O40,Na5PW11Co?(H2O)O39.They were characterized by IR,UV-visible spectroscopy,and TG-DTA.And the results showed that the four POMs was successfully synthesized and they had typical Keggin structure.2 Synthesis and characterization of POM/NH2-SBA-15 hybrid materialsFirstly,we synthesized mesoporous molecular sieve SBA-15,and then used(3-aminopropyl)triethoxysilane(APTES)grafting aminopropyl at the channels of SBA-15 to form NH2-SBA-15.and then re-grafted in aqueous solution obtained POM/NH2-SBA-15 mesoporous hybrid sample series.They were charcterized by IR.UV-vis/DRS,ICP,N2 adsorption isotherms and XRD.The results showed that POM successfully grafted to the NH2-SBA-15 surfaces.And POM remain Keggin type structure,the sample mesoporous hexagonal symmetry of the carrier would be kept.The effect of synthetic hybrid materias between POM/NH2-SBA-15 and the ratio of SBA-1 5 had been investigated,as well as the impact of the different way to remove template to form hybird material,the results showed:(1)POM and the ratio would affect the NH2-SBA-1 5 loading the POM,the number of POM loaded at carrier would increase in pore,but when the ratio of POM and amino was over 1:12,the load of amount would be remained.(2)POM loading in carriers would affect hybrid material pore parameters,and with the load increased,the amount of POM added to walls would increase,and clogged pores,pore volume and surface area of the sample material would become smaller.3.Study of loading method mesoporous hybrid materialsDifferent POMs loaded in carriers had been investigated.At this part,different POMs but the same molar K7Co?W11Co?(H2O)O39,K8Co?W11Co?(H2O)O39,K6Co?W12o40,Na5PW11Co?(H2O)O39 was put at same chemical environment,and then added same carriers,stirred 24 h and stopped the reaction.And after washed and dried,the hybrid materials were characterized by UV-vis/DRS and FT-IR.Besides,we used n-butylamino reacted with POMs as comparison to investigate wheather POMs coordinated with amino or not.The results showed(1)K7Co?W11Co?(H2O)O39 coordinated with amino at carriers and loaded in NH2-SBA-15,but it can not been loaded in carriers that weren't grafted by the aminopropyl,and K8Co?W11Co?(H2O)O39,Na5PW11Co?(H2O)O39 can also be coordinated with amino(2)K6Co?W12O40 also can been loaded in NH2-SBA-15 pore,but it can't confirm which way to load.