催化功能材料_4.经典实例

1、Chapter four: Classic example analysis in homogeneous and heterogeneous catalysis, electrocatalysis and photocatalysis.,By Dr. Yejun Qiu,Department of Materials Science and Engineering Spring, 2011.,(12 credit hours),Homogeneous catalysis; Heterogeneous catalysis; Electrocatalysis; Photocatalysis.,C

2、ontents:,Part I. Homogeneous catalysis.,Example 1: Wilkinsons catalyst RhCl(PPh3)3 tris(triphenylphosphine) rhodium chloride 三-三苯基膦氯化铑,Example 2: Supported aqueous phase catalyst (SAPC),1. Wilkinsons catalyst RhCl(PPh3)3,Brief introduction; Structures of RhCl(PPh3)3; Reaction mechanism; Synthesis of

3、 RhCl(PPh3)3; Characterizations; Expansion: HRh(CO)(PPh3)3, RhCl(CO)(PPh3)2,Brief introduction,RhCl(PPh3)3 is the first highly active homogeneous hydrogenation catalyst (hydrogenation of olefins). Interestingly, the catalytic discovery was made independently and nearly simultaneously by Wilkinson (N

4、obel prize winner for Ferrocene,1973) and Coffey in 1964. Wilkinson fully explored the selectivity, and mechanism by which the complex catalyzes the hydrogenation of olefins and thus the compound is now commonly referred to as “Wilkinsons catalyst.”,Red solid; Soluble in benzene, but insoluble in wa

5、ter; Melting point is bout 245-250 oC; ,Hydrogenation is the addition of H2 to a multiple bond (C=C, CC, C=O, C=N, CN, N=O, N=N, NN, etc) to reduce it to a lower bond order. The most common and simple type of hydrogenation is the reduction of a C=C double bond to a saturated alkane:,Hydrogenation,Th

6、ere are three different ways that transition metal catalysts can activate H2 for performing hydrogenation catalysis:,A metal with d electrons (d2 or higher).,Transition metals with d0 counts.,Ru(+2) is the most common metal.,氢解,异裂,Structures of RhCl(PPh3)3,The compound is a square planar complex;,Th

7、e compound is a 16-electron complex.,Tolmans rule: When the total number of valence electrons of coordination center and ligands is 18 or close to 18 (16), the complex is stable. Such as: Ni(CO)4, Fe(CO)5, Cr(CO)6, Ag(NH3)4+ , Co(NO2)63-, etc.,Ag(NH3)4+: Ag (d9S2d10S1) , Ag+ (d10S0) . :NH3, 24 (coor

8、dinate number) =8. The total number of valence electrons=10+8=18.,RhCl(PPh3)3: Rh (d8S1) Cl, so Rh (d8S0) + and Cl-; Cl-: 2 PPh3: 23=6 The total number of valence electrons=8+2+6=16,Reaction mechanism of RhCl(PPh3)3 catalyst,The mechanism of this reaction involves the initial dissociation of one or

9、two triphenylphosphine ligands to give 14- or 12-electron complexes, respectively, followed by oxidative addition of H2 to the metal. Subsequent -complexation of alkene, intramolecular hydride transfer (olefin insertion), and reductive elimination results in extrusion of the alkane product.,Synthesi

10、s of RhCl(PPh3)3,It was very simply prepared by reacting RhCl3H2O with excess PPh3 in refluxing ethanol. Triphenylphosphine or ethanol serve as the reducing agent.,The reaction temperature is important. To avoid the formation of RhCl3(PR3)3 complex, the relatively high temperature is preferred.,(1)

11、RhCl33(H2O) + 4 PPh3 RhCl(PPh3)3 + O=PPh3 + 2 HCl + 2 H2O; (2) RhCl33H2O + 3 PPh3 + CH3CH2OH RhCl(PPh3)3 + CH3CHO + 2 HCl + 3 H2O.,Characterization,FTIR; Nuclear magnetic resonance (NMR); Electrospray ionization mass spectrometry (ESI-MS).,Infrared Spectroscopy of a Wilkinson Catalyst in a Room-Temp

12、erature Ionic Liquid,NMR,Using NMR and ESI-MS to Probe the Mechanism of Silane Dehydrocoupling Catalyzed by Wilkinsons Catalyst,(硅烷脱氢偶联),1. Rh(PPh3)3Cl; 2. Rh(PPh3)2(Cl)(H) Si(nHex)2H; 3.Rh(PPh3)3H; 4. Rh(PPh3)3(Cl)(H)2; 5. Rh(PPh3)4H.,Variable temperature 145.8 MHz 31P1H NMR spectra.,Reaction profi

13、le showing the evolution of the six most abundant Rh-containing species observed over time by ESI-MS. Each trace is generated by summing the intensities of all related entities and normalizing to the total ion current. Inset: lnRhHP3 vs. time for the decay of this species, demonstrating first-order

14、behavior.,Expansion of Wilkinsons catalyst,RhCl(CO)(PPh3)2; RhCl2(PPh3)2; HRhCl(PPh3)3; HRh(CO)(PPh3)3 HRuCl(PPh3)3; . Anchored Wilkinsons Catalyst.,(RhCl(PPh3)3),RhCl(CO)(PPh3)2,RhCl(PPh3)3 reacts with CO or HCHO to give trans-RhCl(CO)(PPh3)2: RhCl(PPh3)3 + HCHO RhCl(CO)(PPh3)2 + H2 + PPh3; RhCl(PP

15、h3)3 + CO RhCl(CO)(PPh3)2 + PPh3.,HRhCl(PPh3)3,Note that there is no change in oxidation state of the Ru(+2)!,HRuCl(PPh3)3,Osborn later discovered that cationic complexes 阳离子络合物 like Rh(cod)(PPh3)2+ were considerably more active for hydrogenations relative to Wilkinsons catalyst. The reason for this

16、 is that the cationic metal center is more electrophillic and this favors alkene coordination, which is often the rate determining reaction step. Also by only having 2 PPh3 ligands present one could keep the catalyst on the far more reactive catalytic cycle.,cod=1,5-cylcooctadienyl 1,5-环辛二烯, Cy=Cycl

17、ohexyl, py = pyridine, Me=methyl.,Dendritic SBA-15 supported Wilkinsons catalyst for hydroformylation of styrene,Anchored Wilkinsons Catalyst,(APTES: 3-氨丙基三乙氧基硅烷),Structural Characterization, Optical Properties, and Improved Solubility of Carbon Nanotubes Functionalized with Wilkinsons Catalyst,2. S

18、upported aqueous phase catalyst (SAPC),Brief introduction; Basic principles; Several typical processes catalyzed by SAPC; Synthesis of SAPC Characterization; Catalytic activity evaluation.,Brief introduction,This was first referred to as supported aqueous-phase catalysis (SAPC) by Davis in an articl

19、e published in Nature in 1989. In SAPC, a hydrophilic support such as silica is contacted with a water-soluble organometallic complex by aqueous-phase impregnation. After evacuation of the water phase, the organometallic complex becomes distributed on the support. Exposure to water vapor for a fixed

20、 time allows precise amounts of water to condense on the solid surface. The solid, coated by an aqueous film of catalyst, is placed in an immiscible organic phase that contains the reagents. The reactants diffuse from the organic phase into the porous solid, where they react at the water-organic int

21、erface, and the products diffuse back to the bulk organic phase. Along with the advantage of immobilization of the organometallic species, SAPC offers a high surface area for support, which translates into a high interfacial area, and the possibility of selectivity variations from bulk equilibrium p

22、roduct distribution through the effect of the interface.,Supported aqueous phase (SAP),Catalyst: water-soluble transition metal complexes; Support: hydrophilic; (SiO2, controlled pore glass); Catalysts can flow in the surface water film; The surface water content is very important; (excessive water

23、results in lower catalyst concentration; while scant water leads to the poor fluidity of catalyst.),(Basic principles),Chapter four: Classic example analysis in homogeneous and heterogeneous catalysis, electrocatalysis and photocatalysis.,By Dr. Yejun Qiu,Department of Materials Science and Engineer

24、ing Spring, 2011.,(12 credit hours),Part II. Heterogeneous catalysis.,Examples: 1. Ziegler-Natta catalyst; 2. Catalysts for oil refinery; 3. Catalysts for NH3 synthesis; 4. Shape-selective catalysis: Zeolites; 5. Catalytic materials in environmental protection; 6. Uniform, eggshell-type and yolk-typ

25、e catalysts.,1. Ziegler-Natta catalyst,Brief introduction; Structures; Reaction mechanism; Synthesis; Characterizations; Other things.,Brief introduction,Ziegler (18981973) A German chemist who won the Nobel Prize in Chemistry in 1963, with Giulio Natta, for work on polymers.,Natta (19031979) An Ita

26、lian chemist. He won a Nobel Prize in Chemistry in 1963 with Karl Ziegler .,Ziegler-Natta Catalysts are structured by transition metals of groups IV-VIII and metal alkyl with metal of groups I-III.,A Ziegler-Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes (-olefins, CH2=C

27、HR ).,The general expression is:,Major catalyst components：TiCl4， TiCl3，VCl3，VOCl3，ZrCl3，and etc. (TiCl3 is commonly used)； Co-catalyst components: The alkyl compounds of some metals, Such as Be，Mg，Al , and etc.，and among them, AlEt3 and AlEt2Cl are commonly used.,Three types of Ziegler-Natta cataly

28、sts are currently employed: Solid and supported catalysts based on titanium compounds used in combination with cocatalysts (organoaluminum compounds). Metallocene catalysts, combination of various mono- and bis-metallocene, in particular ansa- (or bridged) metallocene complexes of Ti, Zr or Hf. They

29、 are usually used in polymerization reactions in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). Post-metallocene catalysts 后茂金属催化剂 based on complexes of various transition metals with multidentate oxygen- and nitrogen-based ligands. These complex

30、es are also activated with MAO.,The catalyst systems can be homogeneous or heterogeneous.,Structures,TiCl4 and TiCl3 have four crystal structures (， and -type）. Except of type , other three types are octahedral layer structure.,The transition metal is reduced from high oxidation state to low oxidati

31、on state.,Metal alkyl plays important roles in Ziegler-Natta catalyst system.,Reaction mechanism,Coordination polymerization (Complexing polymerization, insertion polymerization: is a form of addition polymerization in which monomer adds to a growing macromolecule through an organometallic active ce

32、nter.,The polymers tend to be linear and not branched and have much higher molar mass.,Elementary reactions of Coordination polymerization,（1）Chain initiation,（2）Chain growth,（3）Chain transfer,（i）Transfer to monomer,（ii）Transfer to monomer metallorganics,（iii）Transfer to H2（H2 is molecular weight mo

33、difier）,（iv）Intramolecular transfer,（4）Chain termination,(ii) O2、CO2、CO，ketones can also result in chain termination.,(i) Chemicals containing reactive hydrogen (Alcohols, arboxylic acids, amines, water, etc.) can react with active sites and thus make them deactivate:,全同立构体 Isotactic,间同立构体 Syndiotac

34、tic,无规立构体 Atactic,Synthesis,A typical process: (MgCl2-supported ZieglerNatta catalyst),support preparation,Dealcoholation treatment,Adding titanium tetrachloride,Washed with hexane,An internal electron donor (ID) and/or an external electron donor (ED) is added simultaneously with co-catalyst.,Charac

35、terization,XRD; XPS; NMR; FTIR; Raman; TEM; BET; etc.,Journal of Molecular Catalysis A: Chemical 278 (2007) 127134,Other things,1. Matters need attention: The polymerization system needs to keep dry; All used chemicals should experience dewatering and deoxidation treatment; The solvents can not cont

36、ain active hydrogen and detrimental impurities; The polymerization should be carried out under the protection of N2 atmosphere; The catalyst residues can be removed by H2O, alcohols or chelons 螯合剂.,2. Methods to further improve the catalytic activities: ultrafine grinding; (to obtained more -type Ti

37、Cl3 and improve surface area) To disperse active components on support surface. Commonly used supports, such as MgC12, Mg(OH)2 , ; The BET value increases from 15m2/g to 75200m2/g; The polymer products contain small amount of catalyst residues.,2. Catalysts for petroleum refining,Catalytic cracking;

38、 catalytic reforming; Hydrogen refining; Hydrocracking; Isomerization; Alkylation; ,Catalytic cracking,Cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon

39、bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts.,Catalysts for Catalytic cracking,Matrix: kaolin; Clay: as adsorbent; Binder: aluminum sol; Additive: ZSM-5.,(SiO2/Al2O3:36),Chain mechanism involves three elementar

40、y steps: initiation, propagation and termination. The initiation step is represented by the attack of an active site on the reactant molecule to produce the activated complex that, in the gas phase or when using liquid superacids, would correspond to the formation of a carbocation 碳阳离子. The chain pr

41、opagation is represented by the transfer of a hydride ion from a reactant molecule to an adsorbed carbenium ion. The termination step corresponds to desorption of the adsorbed carbenium ion to give an olefin whilst restoring the initial active site.,Catalytic cracking mechanism,The initiation step:,

42、Chain propagation:,The chain transfer is terminated when the sur face carbenium ions are desorbed and the Brnsted acid site of the catalyst is regenerated. This step is just the reverse of the adsorption of one olefin and could be written as: With this simple step, the cracking chain mechanism is completed.,Chain termination:,Product distribution and conversion of catalytic cracking for 1C6=,Analyzed by GC. Ag ilent 6890 g as chromatograph; SP-3420 gas chromatograph.,Carbon numbe