CHAPTER 2-表面和吸附

英文版表面和吸附

CHAPTER2

表面和吸附

SurfacesandAdsorption

ChapterOutline

2.12.22.32.42.52.62.72.82.92.102.112.12

Introduction17

CleanSurfaces清洁表面18

Langmuir’sWorkon

TheLangmuirIsotherm21朗格缪尔等温方程TheChemisorptionofHydrogen25氢气的化学吸附TheChemisorptionofMoreComplexMolecules26

多复杂分子的化学吸附

Non-homogeneousSurfaces26

非均相表面

Non-equilibriumAdsorption非平衡吸附27

TheProcessofAdsorption29吸附过程

SomeGeneralizationsonChemisorption34化学吸附的一些理论PhysicalAdsorption36物理吸附

BehaviourofPhysicalAdsorptionIsothermsatValuesofP/Po 0.341

2.1Introduction

Itisgenerallyconsideredthattherearethreestatesofmatter,solid,liquidandgas,although

精炼细分关心

eachofthesecanbefurtherre nedorsubpided.Asfarasyou,asachemist,areconcerned,manyofthereactionswithwhichyouhavehadexperienceoccurineithergasorliquidphaseeventhoughtherearealsomanyreactionsthatoccurinthesolidphase.However,further

界面思考承认thatoneisveryfamiliarwith发生出现thoughtleadsonetorecognizeoccurrencesattheinterface

形成气泡

betweentwoorevenmorephases:theformationofgasbubblesinaliquid,theactionof

腐蚀表面活性剂asurfactantataliquidesolidinterface,corrosionatasolidegasinterface(orasolide

摩擦不饱和

liquidegasinterface),frictionatasolidesolidinterface.Allsurfacesare“unsaturated”inthat看作切创建大块物体theycanformallybethoughtofasbeingcreatedbyslicingthroughabulkphase(see

不饱和具有surfaceenergy(or,asitisocca-Figure2.1).Theseunsaturatedsurfaces,therefore,possess松表面能悬挂的化合价sionallyratherlooselyput,“danglingvalencies”).Thesurfaceenergycancontributetotheall-overenergychangesoccurringwhenaprocessoccursatthesurfaces,whetherthisprocessis

相互作用purelyaphysicalinteractionorachemicalreaction.Thestudyofthechemicalphenomena纯粹粗略的称为

occurringatsuchinterfacescanbelooselytermed“surfacechemistry”and,asnotedinthe

术语包括

previouschapter,thetermcanalsoembracethestudyoftheadsorptionandreactionsof

HeterogeneousCatalysis.DOI:10.1016/B978-0-444-53363-0.10002-7CopyrightÓ2012ElsevierB.V.Allrightsreserved.

17

英文版表面和吸附

18Chapter2

Gas phase

Bulk

Figure2.1:

Schematicrepresentationofthecross-sectionofasurfacegeneratedbycleavingametalcrystal.

moleculesatsolidsurfaces(normallyadsorbed从气体相吸附fromthegasphasebutsometimesfromthe

liquidphase).Whenareactionatasurfaceleadstoanewsurfaceentity本质thatdesorbs

解吸

togiveproductsandresultsintheregeneration重生ofthesurface,wehaveacatalyticprocessandare

dealingwiththe多相催化

understandheterogeneous多相催化作用phenomenonof“heterogeneouscatalysis”(seeSection1.2).Inorderto

catalysis,weshouldhaveagoodunderstandingofthephenomenaof

adsorptionand,to在较小的程度上alesserextent,desorption.解吸附

Thischapteraimstogivethestudentan

understandingofthefactorsdeterminingthebehaviourofsurfacesduringtheadsorption(anddesorption)processesandofhowonewouldstudytheseprocesses.

2.2CleanSurfaces清洁表面

In实验上的itisessential,基本

rst,tobeinaposition位置ordertostudythephenomenonofadsorptionexperimentally,

togeneratecleansurfaces.Theearliestworkonchemisorption化学吸附coincided和一致withthe

developmentofthevacuum真空技术techniquesnecessarytogenerateandmaintain保持cleanChapter1).TheworkofLangmuirwasdriven驱动bythedevelopmentofthe电灯surfaces开始

(see

stayinNernst’slaboratoryinGo¨ttingen.When,in1909,hejoined加入electriclight,initiated

duringhis能斯特哥廷根

General通用电气ElectricinMurray瑞希尔thelaboratoriesHill,New美国新泽西州Jersey,hestartedtoworkontheuseofincandescent

炽热of

laments灯丝forwhatwenowknowastheelectriclightbulb电灯泡

(Figure2.2).Typically,

很典型these lamentsaremadeofthin细钨丝

tungstenwirewhich,whenheatedtotemperaturesabove2000ometalsthatmelt熔化C,giveoutlightinthevisible可见光波长wavelength.atveryhightemperatures,themelting熔点Tungstenisoneofagroupofrefractory难熔

pointoftungstenTmbeingabout

3410oC(Table2.1).Thesurface运动so-calledTamman塔曼温度atomstemperature,Tt,signi cantly

很明显ofametalcanbecomemobileatatemperature,the

belowthemeltingpoint.TheTammantemperatureisgivenby:

因此

Tty0:6Tm(2.1)Hence,thesurfacemobility迁移率oftungstenatomsisnotexpectedtooccuruntil约

ca.2000oC.

Tungstenmetalcanbeoxidizedinairtogive产生

WO3.Atrelativelylowtemperatures,

the

英文版表面和吸附

SurfacesandAdsorption19

Glass bulb

Filament灯丝

Glass-metal seal

Figure2.2:

Schematicrepresentationofanelectriclightbulb.Table2.1:Themeltingpointsofsomerefractorymetals.

熔点

难熔金属

Source:HandbookofChemistryandPhysics,CRCPress.

钝化氧化物形成oxideformsanon-mobilelayerthatpassivatesthesurfaceagainstfurther

多层layersofoxideareHowever,asthetemperatureisincreasedfurther,multiple

不稳定causing解吸andthentheoxidelayerbecomesvolatile,desorptionofWO3.1As排除灯丝被解析oxygenisexcludedfromthe lament,anysurfacelayerofoxideisdesorbed

easily,resultinginacleanandstabletungstensurface,aslongasnoothergases高真空排除ofoxygenfromthe lamentrequirestheuseofhighTheexclusionvacuaanddevelopmentofthemethodsneededtocreatesuchvacuathatledtothe rstincandescentlightbulbs.

Allearlyvacuumapparatuswasmadeofglassandeverylaboratoryusingsuchequipment

玻璃制造者而且研究生

employedoneormoreprofessionalglass-blowers.Further,allresearchstudentsworkingwithsuchsystemsbecamerelativelypro cientamateurglass-blowers.2Atypicalvacuumsystemwas

移动以免

真空装置

相对熟练的业余玻璃制造者

真空装置

1

2

Desorptionofanysurfaceimpuritiestakesplaceatthesametime;further,somesurfaceoxygenmaydesorbasmolecularoxygenratherthanasWO3.

Inthelate1960s,Iworkedinalabora …… 此处隐藏：24486字，全部文档内容请下载后查看。喜欢就下载吧 ……