简介:SAPO-34,asilicoaluminophosphatezeolite,hasbeensynthesizedbythehydrothermalmethodwiththeadditionofdifferentmolecularweightsofpolyethyleneglycol(PEG),andhasbeencharacterizedwithXRD,SEM,N2adsorption-desorption,FT-IR,andNH3temperatureprogrammeddesorption(NH3-TPD).WestudiedSAPO-34asacatalystinthemethanol-to-olefins(MTO)reaction,inafixed-bedreactor.TheresultsshowthatthechainlengthofPEGhasagreatinfluenceontheparticlesizeandmorphologyofSAPO-34.PEGactsasinhibitorinthecrystallizationprocess.WiththeincreaseofthechainlengthofPEGusedinthesynthesis,fromarelativemolecularweightof400-6000,themorphologyofSAPO-34changesgraduallyfromcubictonanoplate-likeandthenchangestocubicagain.Theparticlesizedecreasesmarkedlyatfirstandthenincreasestosomeextent.ThecatalyticstabilityintheMTOreactionalsoincreasesfirstandthendecreases,withallthecatalystshavingalmostthesameselectivitytoolefins.WhenthesampleissynthesizedwithPEG800,theparticlesbecomenanoplate-likewithathicknessof46nmonaverage,andthecatalyticstabilityisappreciablyprolonged,whichisattributedtotheshorterdiffusionpathsofthereactantsinthezeolite.