表面催化反应模拟课件.ppt

1、 Contents Introduction to surface science Experiment on surface scienceIntroductionCO oxidation on various surfacesEpoxidation of ethylene on Ag(111)surface Today and TomorrowIntroduction to surface science1.What to study Surface of solid state materials;adsorption on surfaces;interfaces of s-g、s-l

2、or s-s;membranes or films;solidmicro-particles and so on2.Surface region Extend to the bulk and vacuum for ca.10-153.Significance Almost all adsorption or reactions take place on surfaces Noble prizes in 1986(physics):G.Binnig and H.Rohrer Experiment on surface science1.Experimental techniques AES、A

3、FM、EXAFS、HREELS、PEEM、SEM、STM、UPS、XANES、XPS and so on2.Recent achievementsFunctionalization of STM tip ChemPhysChem 2001(2)361STM images showing No.“0”formed with eight CO molecules on Cu(211).(a)normal tip;(b)CO-functionalised tip.Gold clusters on titania surfaces Science 1998(281)1647;2004(306)252E

4、xperiment on surface scienceCo oxidation turnover frequencies at 300K vs.the size of Au clusters on TiO2 supportActivity of CO oxidation at room tem-perature vs.Au coverage above the monolayer of Mo(112)-(8x2)-TiOx Identification of intermediates during ethylene epoxidation Angew.Chem.2004(43)2918Ex

5、periment on surface scienceC1s spectra after EO was adsorbed on the Ag(111)crystal plane at 100K(130K),and then heated to the indicated temperatures.C1s spectra after EO was adsorbed on the Ag(111)at 225K(250K).286.2287.1284.3Simulation on surface science1.IntroductionComputer powerCalculation progr

6、am Enormous progress in surface computationMain programs:DMOL3;CASTEP;Siesta;VASP 2.CO oxidation over different surfaces CO+O CO2 Co3O4 J.Catal.2002(210)198 CO adsorbed on sublayer Co3+.CO adsorbed on surface exposed Co3+.O(dark grey);Co3+(light grey);Co2+(black);C(white).Conclusion:The initial CO a

7、dsorption occurs at the exposed Co site with the minimum on the potential energy surface at Co-C=1.8 Simulation on surface scienceThe overall energy diagram for two reaction pathways are shown.(a)The abstracted O experiences weaker crystal field(Ow);(b)The abstracted O experiences weaker crystal fie

8、ld(Os).(a)(b)Comparative exothermicities for reaction paths A and B.IIISimulation on surface science Au nano-particles supported on TiO2 Phys.Rev.Lett.2003(91)266102Optimized structures of O2/Au/TiO2(110).(a)side view at the interface of the Au/TiO2 system;(b)O2 adsorption at the Au/TiO2 interface;(

9、c)The transition state for CO reacting with O2 at the interface.Adsorption energies(Ead)and barriers(Ea)for CO oxidation on Au/TiO2(110)and non-supported Au using SIESTA.CASTEP results are listed in parenthesis for comparison.All energies are in ev.a Energy obtained using the structure born from the

10、 six-layer SIESTA calculation.Simulation on surface science CO oxidation on metals and metal-oxides J.Am.Chem.Soc.2004(126)8Geometrical structures of TS of CO+O CO2 on metals and metal oxides.(a)Top view of TS structure on Rh,Pd,Ir or Pt(the bonds of O-CO on Ru or Os are over fcc hollow sites);(b)Si

11、de view of TS structure on metal oxides(inset:a different view of the TS on the metal oxides).Metal(yellow);C(gray);O(red).Calculated Reaction Barriers of CO+O CO2aa R-barrier refers to reduced barriers as defined in the text.OC-O distances are the bond lengths at the TS.Reaction barrier vs.the tota

12、l chemisorption energy(CO and O)in IS for 4d metals and their oxides(a),and 5d metals and their oxides(b).Simulation on surface scienceCalculated Reaction Barriers of CO+O CO2aa R-barrier refers to reduced barriers as defined in the text.OC-O distances are the bond lengths at the TS.Simulation on su

13、rface scienceCs promotion J.Am.Chem.Soc.2004(126)80862.Epoxidation of ethylene on Ag surfaceCompeting oxametallacycle pathways.The surface oxametallacycle,formed by reaction of ethylene and oxygen,reacts via TS1 to form EO,while reacts via TS2 to form acetaldehyde and then be oxidized.Simulation on

14、surface science(Ea)=E(TS2)-E(TS1)(Ea)=Ea(Cs/Ag(111)-Ea(pureAg(111)(Ea)for various Cs coverages and various distances between Cs and relevant adsorbate.Different configurations with unit cells are also shown;A and B indicate different Cs adsorption sites.(a)Density of states(DOS)projected on atomslab

15、eled 1-3 is shown and compared to DOSprojected onto a Ag atom of pure Ag(111).(b)Ea for Cs/Ag(111)(empty squares)and for pure Ag(111)with artificially induced electric fields(filled circles).Today and TomorrowJ.H.Larsen,Ib Chorkendorff,Surface Science Reports 1999(35)163 One of the main arguments fo

16、r the tremendous amounts of surface science studied over the years has been the desire to make new and better catalysts.Surface science has provided the frame work,which today is forming the fundamental understanding of catalysis and is thus providing the tools for designing catalysts with specific properties instead of the trial and error methods used earlier.Theoretical work