LDH的制备、表征及醋酸的丙酮化VIP专享VIP免费

Ž.JournalofMolecularCatalysisA:Chemical1512000185–192www.elsevier.comrlocatermolcataMgrAlhydrotalcites:preparation,characterisationandketonisationofaceticacidKulamaniParida),JasobantaDasRegionalResearchLaboratory,Bhubaneswar751013,Orissa,IndiaReceived28October1998;receivedinrevisedform14May1999;accepted14May1999AbstractMgrAlhydrotalciteswithdifferentMg:AlratioswerepreparedandcharacterizedbyPXRD,FTIR,TGrDTA,basicsitesandnitrogenadsorption–desorptionmethods.ItisconfirmedfromPXRDthatthematerialshavehydrotalcitestructure.ThebasicsitesofthesamplesweredeterminedspectrophotometricallybyirreversibleadsorptionofacidshavingdifferentpKavalueswhichshowedthatthebasicsitesincreaseswithincreaseinMg:Alratio.Thespecificsurfaceareaofallsamplesliesintherange170–231m2rg.Allthesampleswerepredominantlymesoporousinnatureandporediameterslieintherange˚Ž.40–70A.ThesamplewithMg:Alratioof4:1showedhighestspecificsurfaceareaandconversion)86.5%ofaceticacidtoacetonewithhighselectivityat3508C.q2000ElsevierScienceB.V.Allrightsreserved.Keywords:Hydrotalcite;Characterisation;Ketonisation;Aceticacid;Yield1.IntroductionAnionicclays,particularlyhydrotalcites,areclassoflayeredmaterialsofcurrentinterest.Hydrotalciteshavebrucite-likepositivelychargedlayerofmagnesiumandaluminiumhydroxideoctahedrasharingedgestoforminfi-nitesheetsstackedontopofeachotherandareheldtogetherbyhydrogenbonding.DuetoŽ.isomorphoussubstitutionofmetalIIIions,thepositivechargethusgeneratedonthebrucitesheetiscompensatedbytheanionspresentintheinterlayerregion.TheyarerepresentedwŽ.Ž.bythegeneralformulaMIIMIII-1yxxŽ.xxqwnyxŽ.OHA,YHO,whereMIIand2xrnxy2)Correspondingauthor.Tel.:q91-674-481636;fax:q91-674-581637;E-mail:root@csrrlbhu.ren.nic.inŽ.MIIIaredivalentandtrivalentcationssuchasMg2q,Mn2q,Co2q,Ni2q,Cu2q,Zn2qandAl3q,Fe3q,Cr3q,respectively,AnyistheinterlayeranionsuchasCly,NOy,CO2yorany33othermacrocyclicmultivalentanions,etc.,andwxxs0.1–0.331,2.Thermaldecompositionofthesematerialsat4508Cresultsintheformationofhighsurfacearea,basicmixedmetaloxidesduetotheremovalofsurfacialandphysisorbedwater,andcarbondioxidemoleculeswhicharefoundtobepromisingcatalystforbasecat-alyzedreactions.Theactivityandselectivityofthesesolidshavebeenestablishedforseveralreactionssuchasaldolcondensation,olefiniso-merisation,alkylationofketones,etc.Catalyticketonisationbydirectsynthesismethodissimple,economicalandversatile.Ox-wxwxwxidesofthorium3,cerium4,manganese5,1381-1169r00r$-seefrontmatterq2000ElsevierScienceB.V.Allrightsreserved.Ž.PII:S1381-11699900240-X()K.Parida,J.DasrJournalofMolecularCatalysisA:Chemical1512000185–192186wxwxzirconium6,rareearthmetals7aswellaswxalkalineearthmetals8andmetaloxidessup-portedoninorganiccarrierssuchasalumina,silicaortitaniaarefoundtobeactivecatalystforthisreaction.ThepresentworkdealswithasystematicstudyonMgrAlhydrotalcitewithdifferentMg:Alratiosforthevapourphaseconversionofaceticacidtoacetonewhichpro-ceedsaccordingtothegeneralequation:2RCOOHs2RCORqCOqHO1Ž.222.Experimental2.1.MaterialsandmethodsHydrotalciteswithvariousMg:Alratioswerepreparedbycoprecipitationatlowsupersatura-wxtionmethod9.Inthismethod,twosolutions,Ž.AandB,wereaddedatthesamerate50mlrhtoabeakercontaining100mlofdeionisedwaterwhilestirring.SolutionAwaspreparedbymixinganequimolarsolutionsofMgandAlŽ.metalnitrates200mlinthedesiredmolarratios.SolutionBwaspreparedbyd...