The-hydroxylation-of-benzene-to-phenol-over-hetero

ShortCommunicationThehydroxylationofbenzenetophenoloverheteropolyacidencapsulatedinsilicaYanLi,ZhiWang,RizhiChen,YongWang,WeihongXing,JunWang,JunHuang⁎StateKeyLaboratoryofMaterials-OrientedChemicalEngineering,CollegeofChemistryandChemicalEngineering,NanjingTechUniversity,Nanjing210009,ChinaabstractarticleinfoArticlehistory:Received26March2014Receivedinrevisedform2June2014Accepted16June2014Availableonline23June2014Keywords:HydroxylationPhenolVanadiumHeteropolyacidHeterogeneousThevanadium-substitutedheteropolyacid(H5PMo10V2O40nH2O)(PMoV2)wasencapsulatedinsilicaasanimmobilizedcatalyst(PMoV2@SiO2)forthehydroxylationofbenzenetophenolwithH2O2.ThePMoV2@SiO2waspreparedbytheone-pothydrolysisoftetraethylorthosilicate(TEOS)withPMoV2andPluronicP123,andthentheP123wasremovedbypyrolysisat500°[e-mail]2@SiO2wasfoundtobehighlyporouswithmicropores,mesoporesandmacropores,andthePMoV2@SiO2washighlyactiveandselectiveforthehydroxylationofbenzeneundermildconditions.Moreover,thecatalystcanbereusedatleast5timeswithoutobviousdeactivation.©2014ElsevierB.V.Allrightsreserved.1.IntroductionAsanimportantintermediateforsynthesizingphenolresins,capro-lactam,fibers,andmanyotherchemicals[1],phenolisindustriallymainlyproducedbythethree-stepcumeneprocesswithhighenergyconsumption,lowyields(ca.5%basedontheinitialbenzene),andenvi-ronmentpollution[2,3].Fromtheviewpointsofeconomyandtheenvi-ronment,theone-stephydroxylationofbenzenetophenolishighlyattractive[4]comparedtothethree-stepcumeneprocessandothermethodsfortheproduceofphenol,suchasnucleophilicsubstitutionofarylhalidesandchlorination/sulfonationprocessesofbenzene[5,6].Recently,theoxidantsforthedirecthydroxylationofbenzenetophenolhavebeeninvestigatedextensively,includingnitrousoxide[7,8],hy-drogenperoxide[4,9],molecularoxygen[2,10],aswellasamixtureofoxygenandhydrogen[1].Amongtheseoxidants,hydrogenperoxideisawisechoicesinceitischeapandefficientwithnontoxicwaterastheonlyby-product.Althoughthedirecthydroxylationofbenzenetophenolwithhydro-genperoxideinliquidphasehasbeenexploredextensively,theprocessisassociatedwithapoorselectivity,namely,asubstantialoveroxidationofphenoloccurs,formingvariousby-products,suchascatechol,hydro-quinone,andbenzoquinone[11].Theone-stephydroxylationofben-zenetophenolwithH2O2isstillaninterestingtopic,andefficientcatalystsarethemainresearchobjectives.TransitionmetalcatalystshavebeendevelopedfortheoxidationofbenzenewithH2O2,includingTi,Fe,CuandV[12–15],butthecatalystswerelimitedinlowselectivityorbadreusability.Tanevetal.[4]Investigatedthecatalytichydroxyl-ationofbenzeneoverTi-MCM-41,whichshowed68%conversionand98%selectivitytowardsphenolundermildreactionconditions.Con-trastingly,theconversionofbenzenewasabout31%with95%selectiv-itytophenolovertitaniumsilicalite-1(TS-1)forthehydroxylationofbenzenewithhydrogenperoxide.CuonMCM-41wasreportedtobeac-tiveforthehydroxylationofbenzene,whichgave21%conversionofbenzeneand94%selectivitytophenol[16].Fe-MCM-41wasalsofoundtobegoodcatalystforthehydroxylationofbenzenetophenol[17].Inaddition,V-containingcatalystswerestudiedextensivelysinceVwasanactivecenterforthehydroxylationofbenzenetophenolundermildconditions.VanadiumoxideonclaywasreportedascatalystforthehydroxylationofbenzenetophenolwithhydrogenperoxidebyXuetal.[18],and14%conversionand94%phenolselectivitywereob-tained.Vanadylacetylacetonatecomplexgraftedtoperiodicmesopo-rousorganosilicawasreportedasacatalystforthehydroxylationofbenzene,whichshowedhighselectivitytowardsthephenolandgoodrecyclability[19].KeggintypephosphovanadomolybdicacidsupportedonaminefunctionalizedSBA-15wasdevelopedandappliedforthehy-droxylationofbenzenewith20%conversionofbenzeneand95%selec-tivitytowardsphenol[20].Thedrawbackofthetransitionmetalcatalystsisthelowselectivity,andtheheteropolyacidcatalystswerelimitedinthereusability.Thusthedevelopmentofefficientandreus-ablecatalystsishighlydesirableforthehydroxylationofbenzenetophenol.Recently,immobilizedheteropolyacidcatalystsweredevelopedandappliedforrelatedreactions,andthusthecatalystswererecycledeasily[21,22].Wehaddevelopedthepolyoxometalate(POM)–ionichybridcatalystsandusedasefficientandreusablecatalystsfortheCatalysisCommunications55(2014)34–37⁎Correspondingauthor.Fax:[phone].E-mailaddress:[e-mail](J.Huang).©2014ElsevierB.V.Allrightsreserved.ContentslistsavailableatScienceDirectCatalysisCommunicationsjournalhomepage:[23].Furthermore,theencapsulatedheteropolyacid(HPA)H3PW12O40wasreportedtobehighlyactivefortheesterification[22].Andhere,wedevelopedanewstrategyforsynthesizingtheV-containingcatalystPMoV2@SiO2byhydrolyzationoftetraethylorthosilicate(TEOS)withKeggintypePMoV2andnonionic(PluronicP123).Andthentheprecatalystwaspyrolyzedat500°[e-mail]2@SiO2wascharacterizedbyFouriertransforminfraredspectra(FT-IR),X-raydiffraction(XRD),andN2ad-desorption,andthePMoV2@SiO2wa