沸石分子筛Word文档格式.docx
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沸石分子筛Word文档格式.docx
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zeolite"
isstillthesubjectofdiscussion[1][2][3][4].Aversion版本ingeneraluseisduetoBARRER[1]andBRECK[5],whichstatesthatzeolites[1318-02-1]arecrystalline结晶的,hydrated含水的aluminosilicateswithaframeworkstructure.Theirthree-dimensional空间的,polyanionicnetworksareconstructedofSiO4andAlO4tetrahedralinkedthroughoxygenatoms.Dependingonthestructuretype,theycontainregular规则的channelsorinterlinked连接voids空间whoseaperture孔diametersareinthemicroporerange.Theseporescontainwatermoleculesandthecations阳离子necessarytobalancethenegativechargeoftheframework.Thecations,whicharemobileandcanbeexchanged,aremainly主要地alkalimetaloralkalineearthmetalions.
Formula分子式1accords符合withthesecharacteristics.Theexpression表达enclosed被附上的inthesquarebrackets括弧showsthecomposition合成物oftheanionic阴离子的frameworkinthecrystallographicunitcell.Mrepresents象征thenonframeworkmetalcation,andnisitscharge.Formula2occursfrequentlyintheliteratureand,unlikeFormula1,simplyrepresentstheoverallchemicalcomposition.
Mx/n[(AlO2)x(SiO2)y]?
zH2O1
M2/nO?
Al2O3?
y?
SiO2?
z?
H2O2
Manysyntheticzeolitesalsooccurnaturallyasminerals.Theobservation观察thatacertainmineralbegantobubble泡沫onstrongheatingledCRONSTEDTin1756togivethename"
zeolites"
tosuchmaterialsfromtheGreekzeo:
toboilandlithos:
stone[6],[7].However,zeolitesonlybecameofindustrialimportanceinthe1950s,whensyntheticexamplesbecameavailableonanindustrialscale等级[8].Sincethen,worldconsumption消费ofsyntheticzeolitesinthefieldsofionexchange,adsorption,andcatalysishasgrowncontinuously连续地.Thetotalfor1993exceeded106t,mainlyaconsequence结果oftheuseofthezeoliteNaAasadetergent洗涤剂builder.Zeolitesarealsoimportantasadsorbentsforseparatingandpurifyingsubstancesandascatalystsinanumberofimportantprocessesinthechemicalandpetrochemicalindustries.
Inaddition,ca.300000t/anaturalzeolitesaresoldworldwide.Theirmainusesareasionexchangersforwatertreatment,insoilimprovement,inanimalfeeds,incatlitter仔,andinpozzolanic凝固性的cement水泥.
Thewiderangeofcommericalapplicationshasstimulated刺激intensive强烈的、精深的investigationofthechemistryandphysicsofthezeolites[5],[9][10][11][12][13][14][15][16][17][18][19].Currentresearchisincreasinglyconcernedwithzeolite-likemolecularsieves,whichhaveexpandedthefieldofzeolitesenormously巨大地duringthelasttwodecades.Inthesenewmaterials,thealuminumandsiliconoftheclassical古典的zeolitesarepartially部分地orcompletelyreplacedbyotherelements[20],[21].Themostimportantgroupsofthesemolecularsievesare:
1)Modificationsofsilica("
zeosils,"
see?
Silica-8.2.1.Zeosils)
2)Metallosilicateswithtri-andtetravalent四价的heteroatoms杂原子inplaceofaluminumasframeworkcomponents,e.g.,boro-andgallosilicates[22],ferrisilicates[23],andtitanosilicates[24]
3)Alumino-andgallophosphatesandcompoundsderived起源fromthem[25][26][27]
Thesecompoundsgenerallyhaveframeworkstructuresanalogous类似的tothoseofthezeolites.Somenewstructureshavebeendiscovered,too.However,withafewexceptions例外,thesecompoundsarestillofratherlimitedeconomicimportance,andarediscussedhereonlybriefly.简要地
2.Nomenclature命名法
Thenamingofzeolitesintheliteratureseldom很少followsascientificsystem.Ifnaturalanalogs类似物exist,thesyntheticzeolitesareoftennamedaftertheminerals(e.g.,faujasite八面沸石,mordenite发光沸石,ferrierite镁碱沸石,andoffretite).Alternatively二者择一地,thenamesgivenbythediscoverersareused.Inthe1950sandearly1960s,newsyntheticzeoliteswerenamedusingthelettersoftheLatinandGreekalphabets.ExamplesincludetheLindemolecularsievesA,L,X,andYofUnionCarbide碳化物andthezeolitesbeta,rho,theta-1,andomega.Acronyms只取首字母的缩写字thatindicatetheindustrialoruniversitylaboratorythatfirstsynthesizedagivenmaterialwerethenincreasinglyused,supplemented补充byaconsecutive连贯的numbering编号方式system.NamessuchasZSM-5(MobilOil),Nu-13(ICI==ImperialChemicalIndustriesLtd英国化学工业公司),LZ-210(UnionCarbide碳化物/UOP==UniversalOilProductsCompany万国油品公司[美]),CSZ-3(Grace人名),andECR-1(Exxon)havegradually逐渐becomegenerallyaccepted公认的.
Zeoliteswithidentical同一的frameworkstructurescanthereforeappearintheliteratureunderdifferentnames.Someorderhasbeenimposed利用bytheintroductionofaclassificationsystemintheAtlas图集ofZeoliteStructureTypes[28],whichindicateswhichdifferentmaterialshavethesamestructuretype.Thestructuretypesthemselvesaredenoted指示bythecombinationofthreecapital大写字母letters.Forexample,thetypeLTAisfoundinzeoliteA,FAUinthefaujasites八面沸石XandY,andMFIintheZSM-5familyofzeolites.
CASnumbersareavailableforonlyafewzeolites.Moreover,asthesearerarely很少地used,theyareoflittlebenefit帮助inliteraturesearches.
3.Structure,Composition,andPropertiesofZeolites
3.1.Framework骨架StructureandPositionsofNonframeworkCations
ThethirdeditionoftheAtlasofZeoliteStructureTypes[28],publishedin1992,describes85differentstructures,includingbothclassicalzeolitesandzeolite-likemolecularsieves.Themajority多数的ofthesestructurescanberepresented描述byFormulas1and2,butafewhavebeenfoundtooccuronlyasalumino-orgallophosphates.
Zeolitesareclassifiedstructurallyastectosilicates网硅酸盐[3].ThebasicelementsoftheirframeworksareTO4tetrahedra(T=Si,Al)linkedthroughoxygenatoms.Thedescriptionandclassificationofthetopology布局ofzeolitesisbasedontheconceptoflargerunitsknownassecondarybuildingunits(SBUs)[28].Thesecanconsist,forexample,ofsimpleringsandprisms棱柱ofvarioussizes.Bycombiningsuchbasicunitstheknownzeoliteframeworkscanbeconstructed构造.Alternative二中选一的conceptsarebasedonmorecomplexchainsorlayer层structuresknownasstructuralsubunits亚层、亚组(SSUs)[29].
Themostreadilyvisualized想象的structuralunitsarepolyhedrasuchasthetruncated切去顶端的octahedraknownassodalite方钠石cages笼orb-cages,foundinthestructureoftheindustriallyimportantzeolitesA,X,andY.Figure
(1)showsthesodaliteunitandtheframeworkstructuresofthezeolites.Inthisrepresentation陈述,thetetrahedrallycoordinatedsiliconandaluminumatomsaresymbolizedbyvertices,andtheoxygenatomsarelocatedbetweenthese.
Theprincipalcharacteristicofallthestructuresisthewell-definedsystemofregular规则的cavities洞orchannelswhichisessential基本的forapplicationofzeolitesasmolecularsieves.InzeoliteA(typeLTA),theb-cages笼arelinkedtogetherviacubic立方体的unitstoformalargercavitywiththeshapeofatruncated切去顶端cubo-octahedron.Theseso-calleda-cages(diameter1.14nm)areinterconnectedbywindowsformedbyringsconsistingof8Tatoms,givingathree-dimensionalporesystem.Iftheb-cagesarelinkedtogetherbyhexagonal六角形prisms棱,thisresultsinthefaujasite八面沸石structure(typeFAU).Inthiscasealso,thelinkingleadstoalargercage.Thisisknownasasupercagebecauseofitslargediameter(ca.1.20nm),andhaswindowsformedby12Tatoms.
Whereas然而thecavitiesintheLTAandFAUstructuretypesarecharacteristicallyintheformofinterlinkedcages,theMORtype(mordenite发光沸石)andtheMFItype(e.g.,ZSM-5)contain包含channelsystems,asshowninFigure
(2).TheMFIstructureiseasiertovisualizeifonlythecavitystructureisrepresented描绘,andnottheframeworkstructure.Linearparallel平行ten-ringchannelsarelinkedtogetherbyzig之字形-zag急转shapedcontinuousporeswithten-ringapertures孔perpendicular垂直tothechannels,resultinginathree-dimensionalcavitysystem.Incontrast,theporesystemofmordeniteistwo-dimensional,the12-ringchannelsbeingineffectonlyone-dimensional.
Thevariouszeolitestructuresdiffernotonlyinthetypeanddimensionalityoftheirporesystems,butalsointhesizeoftheporeapertures.Narrow-pore,medium-pore,andwide-porezeoliteshavedifferentporeaperturesformedbyringsof8,10,or12Tatoms,withcorrespondingcrystallographicdiametersof0.35?
0.45,0.45?
0.60,and0.60?
0.80nm[5],[30].Inthezeolitesthemselves,poreapertureslargerthanthesehavenotsofarbeenobserved,althoughtheydooccurinthealumino-andgallophosphates,inwhichstructurescontaining14-,18-,and20-ringaperturesareknown,withdiametersrangingfrom0.80to1.45nm[31],[32].TheporeaperturesoftheindustriallyimportantsyntheticzeolitesarelistedinTable
(1),togetherwithothercharacteristicdataforthesematerials[5],[30],[33].Itcanalsobeseenfromthetablethattheaperturescandeviatetovaryingextentsfromcircular.Forexample,thecross-sectionofthezig-zagporesinZSM-5isdistinctlyelliptical.
Theregularnatureoftheporesandtheirapertures,whosedimensionsareofthesameorderofmagnitudeasmoleculardiameters,enablesthezeolitestofunctionasmolecularsieves.Thisistheoutstandingpropertyofzeolitesthatgivesthemtheirvalueasselectiveadsorbentsforseparatingsubstancesandasshape-selectivecatalysts(seeSections7.2.Adsorptionand7.3.Catalysis).Dependingonthezeolitetypeanditsporesystem,moleculescanpenetrateintothecavitysystemorbeexcludedfromit(Fig.(3)).
Theconceptsofkineticmoleculardiameterandeffectiveporesizetakeaccountofthefactthattheadsorptivemoleculesandthezeoliteframeworkarenotrigid,butundergothermalvibrations.Therefore,theselectivityoftheexclusionofmoleculeswhosediametersaresimilartothatofthezeoliteaperturesdeterminedcrystallographicallydependso
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