催化功能材料 4經(jīng)典實(shí)例

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

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

3、h3)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 (Nobel pr

4、ize 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 water; Me

5、lting 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:HydrogenationThere are thr

6、ee 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. 氫解異裂 Structures of RhCl(PPh3)3 The compound is a square planar complex; The compound is

7、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 (coordinate number) =8

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

9、 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. Synthesis of RhCl(PPh3)3It was

10、 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) RhCl33(H2O) + 4 PPh3 RhC

11、l(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-Temperature Ionic Liquid NMRUs

12、ing NMR and ESI-MS to Probe the Mechanism of Silane Dehydrocoupling Catalyzed by Wilkinsons Catalyst(硅烷脫氫偶聯(lián))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.Electrospray ionization mass spectrometry (ESI-

13、MS).電噴霧串聯(lián)質(zhì)譜Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized. Reaction profile showing the evolution of the six most abu

14、ndant 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 behavior. Expansion of Wilkinsons catalyst R

15、hCl(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)2RhCl(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(PPh3)3 + CO RhCl(CO)(PPh3)2 + PPh3.HRhCl(PPh3)3Not

16、e that there is no change in oxidation state of the Ru(+2)!HRuCl(PPh3)3Osborn later discovered that cationic complexes 陽離子絡(luò)合物 like Rh(cod)(PPh3)2+ were considerably more active for hydrogenations relative to Wilkinsons catalyst. The reason for this is that the cationic metal center is more electroph

17、illic 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-環(huán)辛二烯, Cy=Cyclohexyl, py = pyridine, Me=methyl.Dendritic SBA-15 sup

18、ported Wilkinsons catalyst for hydroformylation of styreneAnchored 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 Catalyst2. Supported aqueous phase catalyst (SAPC) Brief introductio

19、n; 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 article published in Nature in 1989. In SAPC, a hydrophilic su

20、pport 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 time allows precise amounts of water to condense on the

21、 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 interface, and the products diffuse back to the bulk organi

22、c 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 product distribution through the effect of the interface.

23、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 results in lower catalyst concentration; while scant wate

24、r 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 QiuDepartment of Materials Science and EngineeringSpring, 2011.(12 credit hours)Part II. Heterogeneous catal

25、ysis.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-type catalysts.1. Ziegler-Natta catalyst Brief introduction; Structures; R

26、eaction mechanism; Synthesis; Characterizations; Other things. Brief introductionZiegler (18981973) A German chemist who won the Nobel Prize in Chemistry in 1963, with Giulio Natta, for work on polymers. Natta (19031979)An Italian chemist. He won a Nobel Prize in Chemistry in 1963 with Karl Ziegler

27、. 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=CHR ). MtIV-VIIIX + MtI-IIIRMajor catalystCo-catalyst The general expressio

28、n 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 catalysts are currently employed:

29、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 are usually used in polymer

30、ization reactions in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). Post-metallocene catalysts 后茂金屬催化劑 based on complexes of various transition metals with multidentate oxygen- and nitrogen-based ligands. These complexes are also activated with M

31、AO. 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 oxidation state. Metal alkyl plays

32、important roles in Ziegler-Natta catalyst system. Reaction mechanismCoordination polymerization (Complexing polymerization, insertion polymerization: is a form of addition polymerization in which monomer adds to a growing macromolecule through an organometallic active center.The polymers tend to be

33、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 modifier）（iv）Intramolecular transfer（4

34、）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:全同立構(gòu)體Isotactic間同立構(gòu)體Syndiotactic無規(guī)立構(gòu)體Atactic SynthesisA typical process:

35、 (MgCl2-supported ZieglerNatta catalyst)support preparationDealcoholation treatmentAdding titanium tetrachlorideWashed with hexaneAn internal electron donor (ID) and/or an external electron donor (ED) is added simultaneously with co-catalyst. Characterization XRD; XPS; NMR; FTIR; Raman; TEM; BET; et

36、c.Journal of Molecular Catalysis A: Chemical 278 (2007) 127134 Other things1. Matters need attention: The polymerization system needs to keep dry; All used chemicals should experience dewatering and deoxidation treatment; The solvents can not contain active hydrogen and detrimental impurities; The p

37、olymerization should be carried out under the protection of N2 atmosphere; The catalyst residues can be removed by H2O, alcohols or chelons 螯合劑. 2. Methods to further improve the catalytic activities: ultrafine grinding; (to obtained more -type TiCl3 and improve surface area) To disperse active comp

38、onents 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; catalytic reforming; Hydrogen refining; Hydrocracking

39、; 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 bonds in the precursors. The rate of cracking and the en

40、d 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 elementary steps: initiation, propagation and termination. The ini

41、tiation 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 碳陽離子. The chain propagation is represented by the transfer of a hydride ion

42、 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 mechanismThe initiation step:Chain propagation:The chain transfer is terminated when the

43、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