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1、Chapter two: Relationship between,surface structures of catalytic materials,and their catalytic properties,(4 credit hours),By Dr. Yejun Qiu,Department of Materials Science and Engineering,Spring, 2011.,?,Electron structure,?,Crystal structure,?,Defect structure,?,Surface,acid,or,base,sites,(importa
2、nt,acid-base catalysis),?,Skeleton structure (Example: zeolite),?,Size effect (Nano effect),for,1.,Electron structure,?,Atomic Orbital Theory (,原子轨道理论,);,?,Molecular Orbital Theory (,分子轨道理论,);,?,Band theory (electron structure of solid).,1.1. Atomic Orbital Theory,?,electron cloud and atomic orbital
3、:,1,s,2,s,2,p,x,2,p,y,2,p,z,2,d,z,d,xz,d,yz,d,xy,2,2,d,x,-y,The,atomic,orbital,model,is,the,currently,accepted,model,of,the,placement,of,electrons,in an atom.,Na:,?,The order of Atomic Orbital Energy:,?,Energy shell (n = 1,、,2,、,3,、,4,、,5,、,6),?,Energy level (s, p, d, f),（,1,）,Same energy shell, nsn
4、pndnf;,（,2,）,Same energy level, 1s,2s,3s,4s,;,（,3,）,Same energy shell, different atomic orbital,2px=2py=2pz, etc.;,（,4,）,Different energy shell and energy level: 1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s,E,n,e,r,g,y,Pauli approximate,energy level diagram,?,Filling of orbital,?,Pauli exclusion
5、principle: “no two electrons in the same atom can,be in the same quantum state.”,One atomic orbital can contain two electrons at most and the spin direction is,opposite.,?,Hunds,rule is an observational rule which states that a greater,total spin state usually makes the resulting atom more stable.,E
6、very orbital in a subshell is singly occupied with one electron before any,one orbital is doubly occupied, and all electrons in singly occupied orbitals,have the same spin.,d-orbital,p-orbital,?,Stable electron configuration:,A,stable,electron,configuration,refers,to,an,atom,in,which,the,outer,elect
7、ron,shell is unoccupied, half-full or full.,24Cr,：,Ar3d,5,4s,1,(3d,4,4s,2,),29Cu,：,Ar3d,10,4s,1,(3d,9,4s,2,),Generally,more,unoccupied,d-orbitals,are,beneficial to catalytic reactions.,1.2. Molecular orbital theory,?,One of chemical bonding theories,?,Molecular orbitals are obtained by combining the
8、 atomic orbitals on the,atoms in the molecule.,Example: the formation of H-H bond.,This diagram suggests that the energy of an,H,2,molecule,is,lower,than,that,of,a,pair,of,isolated atoms. As a result, the H,2,molecule,is more stable than a pair of isolated atoms,.,Examples: O,2,and F,2,Examples:B,2,
9、 C,2, and N,2,Molecular orbitals of benzene,?,delocalized molecular orbital: In the benzene ring, the,bonds are delocalized,and form around the entire ring, forming a torus (doughnut-shaped) orbital above,and below the sigma bond.,Examples: CH,2,=CH-CH=CH,2,1.3. Energy band structure,Why bands occur
10、 in materials?,The electrons of a single isolated atom occupy,atomic orbitals, which,form,a,discrete,set,of,energy,levels.,If,several,atoms,are,brought,together into a molecule, their atomic orbitals split, as in a,coupled,oscillation,.,This,produces,a,number,of,molecular,orbitals,proportional to th
11、e number of atoms. When a large number of atoms,(of order,1020 or more) are brought together to form a solid, the,number,of,orbitals,becomes,exceedingly,large.,Consequently,the,difference,in,energy,between,them,becomes,very,small.,Thus,in,solids,the,levels,form,continuous,bands,of,energy,rather,than
12、,the,discrete,energy,levels,of,the,atoms,in,isolation.,However,some,intervals of,energy contain,no orbitals, no,matter,how,many atoms,are aggregated, forming,band gaps,.,Metal: Fe, Co, Ni,;,Semiconductor:,Ge(0.66eV), Si(1.12eV),TiO,2,(3.23eV),ZnO(3.3eV),GaAs(1.42eV),GaN(3.44eV), ,Insulator: rubber,c
13、eramics,Comparison of the band gaps,for,a,metal,a,semiconductor,and an insulator.,Energy Band Structure,Density of States (DOS),1.4. Effect of electron structure on catalysis,Example: Photocatalysis,is the acceleration of a photoreaction in the,presence of a,catalyst,.,Band gap:3.23 eV, 387.5 nm,E(e
14、V) =1240 /,（,nm,）,Visible light (400-760nm):,50%;,Infrared light(760nm):,43%;,UV-light(400nm): 7%.,In photogenerated catalysis, the photocatalytic activity (PCA) depends on the ability,of the catalyst to create,electron,hole pairs, which generate,free radicals,(,hydroxyl,radicals,: ,OH) able to unde
15、rgo secondary reactions.,Eigen value (,E,) of the outer orbital of the BO,6,9-,(B = Ti - Ni) clusters,Photocatalytic activity,文献：桑丽霞,傅希贤,白树林,杨秋华,王俊珍,曾淑兰,.,感光科学与光化学, 2001,19(2):109-115,2.,Crystal structure,To be continued,！,Chapter two: Relationship between,surface structures of catalytic materials,a
16、nd their catalytic properties,(4 credit hours),By Dr. Yejun Qiu,Department of Materials Science and Engineering,Spring, 2011.,3. Defect,structure,?,point defect,?,linear defect (dislocation),Impurity,Conductive mechanism of ZrO,2,electrolyte.,(a) Atomically resolved STM image of a defective FeO isla
17、nd (15 nm,15 nm) (,V,b =,100,mV,I,= 0.02 nA); (b) Zoomed O vacancy clusters in (a); (c) Schematic drawing of missing O,atoms (the blue balls with dotted lines) at fcc sites; (d) STM image from a perfect 1.0 ML,FeO film (10 nm,10 nm) (,V,b = 800 mV,I,= 0.6 nA).,马腾,傅强,姚运喜,崔义,谭大力,翟润生,包信和,.,催化学报, 2010,
18、31(8): 1013-1018.,Temperature,of,the,top,of,catalyst,bed,(,T,b,),and,furnace,temperature (,T,f,),4. Surface acid or base sites,?,A Lewis acid is defined to be any species that accepts lone pair electrons.,?,A Lewis base is defined to be any species that donates lone pair electrons.,Example: H,+,is a
19、 Lewis acid, since it can accept a lone pair, while OH,-,and,NH,3,are Lewis bases, both of which donate a lone pair.,Me,3,B + :NH,3, Me,3,B:NH,3,Me,3,B,-NH,3,-,?,BF,3,+ F, BF,4,3,d,2,?,2?,sp,SiF,4,+ 2 F, SiF,6,RCl +AlCl,3, R,+,+ AlCl,4,?,Lewis,diagrams,showing,the,formation of the ammonium ion.,IR,C
20、CN spectra of pyridine (Py)-,adsorbed species established on the,various,test,magnesias,following,thermoevacution,at,10,-5,Torr,and,the,temperatures,indicated,for,5,min.,Desorption Thermogravimetry and Calorimetry of Room-Temperature,Adsorbed Pyridine (Py) and CO,2,Molecules on the Test Magnesias,Ex
21、ample of acid catalysis,Esterification mechanism,Acid and base catalyzed aldol mechanism,Aldol condensations are irreversible.,Acid catalyzed dehydration,Base catalyzed dehydration,5. Skeleton structure,Zeolites,are,microporous,crystalline,aluminosilicates,composed,of,TO,4,tetrahedra,(T,=,Si,Al),wit
22、h,O,atoms,connecting,neighboring,tetrahedra.,For,a,completely,siliceous,structure,combination,of,TO,4,(T,=,Si),units,in,this,fashion,leads,to,silica,(SiO,2,),which,is,an,uncharged,solid.,Upon,incorporation of Al into the silica framework, the +3 charge on,the,Al,makes,the,framework,negatively,charge
23、d,and,requires,the presence of extraframework cations (inorganic and organic,cations can satisfy this requirement) within the structure to keep,the overall framework neutral. The zeolite composition can be,best described as having three components:,The amount of Al within the framework can vary over
24、 a wide range with Si/Al,= 1 to,.,Table: The Evolution of Molecular Sieve Materials,Comparison of pore sizes of different framework structures.,The,construction,of,four,different,zeolite,frameworks,with,sodalite,or,h,cages.,A,pair,of,TO,4,tetrahedra,is,linked,to,a,single,sodalite,cage,by,T-O-T,bonds
25、.,In,a,less,cluttered,representation, the oxygen atoms,are omitted and straight lines are,drawn connecting the tetrahedral,(T) atoms. The sodalite cage unit,is,found,in,SOD,LTA,and,FAU,-EMT frameworks.,The cooperative templating effect of amine in the ionothermal synthesis (here the amine is n-DPA).
26、,裴仁彦,徐云鹏,魏,莹,温国栋,李科达,王,磊,马怀军,田志坚,林励吾,.,催化学报, 2010, 31(8): 1083-1089.,Effect of pore diameter on molecular diffusivity, showing that intrazeolitic diffusion (,晶体内,的扩散,) can span more than 10 orders of magnitude.,In,the,range,of,porosity,typically,found,in,zeolites,the,intracrystalline,diffusivities,c
27、an,change,by,12,orders,of,magnitude,depending,on,the,pore,size and the size and shape of the molecule diffusing through the zeolite,Reactant,selectivity,Product,selectivity,Restricted,transition-,state,selectivity,6. Size effect (Nano effect),?,Specific surface area increases greatly;,?,Melting poin
28、t decreases obviously;,?,Energy levels split.,Example: Au,?,BET: bulk materials (0.1 m,2,/g); 2nm (300 m,2,/g).,?,Melting point: bulk materials (1064,o,C); 2nm (327,o,C).,Example: Growth of carbon nanotubes,(a),Typical,SEM,and,(b),AFM,images,of,the,as-,grown,SWNTs,on,Si/SiO,2,substrate covered with
29、a 30-,nm-thick,sputtering,deposited,SiO,Raman,spectra,2,film.,(c),of,the,same,sample,acquired,at,three,positions,with,the,peaks,at,303,cm-1,originating,from,Si/SiO,2,substrate,and,used,for calibration. (d) HRTEM,image,of,three,individual,SWNTs,(indicated,by,arrows).,Raman,spectra,of,(A),SWNTs,within,the,circle,trace,area,and,(B),MWNTs,or,carbon,filement,inside,the,circle,trace.,SEM,images,of,aligned long SWNT arrays from (C),SiO,2,(D),Al,2,O,3,(E),TiO,2,and,(F),Er,2,O,3,Random SWNTs from TiO,2,NPs (a), Al,2,O,3,NPs (b) and rare earth oxides Er,2,O,3,NPs,
