工业催化原理-英文课件chapter22old

1、2.2 Catalysis by transition metal complexes,Catalysis by transition metal complexes has been widely used in chemical reactions such as polymerization, oxidation, isomerization, hydroxylation, carbonylation 2.2.1 Organometallic complexes Organometallic complex used as catalyst is generally composed o

2、f a metal atom or ion in the center with several atoms or groups of atoms called ligands（配体）bonded around to form a polyhedron,2.2.1 Organometallic complexes,General geometry of complex Octahedral complex with six surrounding ligands, hybridization scheme d2sp3 Tetragonal pyramidal complex with five

3、 ligands and dsp3 hybridization Tetrahedral or square planar complex with four ligands, hybridization scheme is sp3 and dsp2 respectively,2.2.1 Organometallic complexes,Transition metal: Pd, Pt, Ni, Co, Fe, Rh, Ru . 钯、铂、镍、钴、铁、铑、钌. Ligand: NH3, CO, Cl-, C2H4 . The catalytic action of complexes usuall

4、y results from the interaction of ligands in coordination sphere with the central metal to change their chemical bonding activation,Complex of Pt2+ and ethylene - complexing,2.2.2 Samples of complex catalyzed reaction,Catalyzed hydrogenation of ethylene Catalytic complex: square planar structure Rh+

5、Cl(PPh3), triphenyl phasphine Possible mechanism: complex Rh+ClL3 dissociation unsaturated coordinate complex oxide-additive reaction with hydrogen Rh3+ClL2H2 octahedral complex complexing with ethylene desorption of ethane,Mechanism of hydrogenation of ethylene,Advantage of the metal complex cataly

6、sts,In general, molecules of complex catalyst is well dispersed in the solvent so that it usually has very high activity. The central metal ion and the surrounding ligands can be widely selected, especially part of or all the ligands can be specially changed to match the critical requests of the rea

7、ction, leading high product selectivity,2.2.2 Samples with industrial significance,Preparation of aldehyde from ethylene oxidation, Wacker reaction. C2H4 + O2 CH3CHO catalyst: Pd2+Cl4 planar complex Propene polymization with Ziegler-Natta catalyst: TiCl3 Al(C2H5)2 Methanol carbonylation CH3OH + CO C

8、H3COOH catalyst: Rh(CO)2I2,2.2.2 Samples with industrial significance,Methanol carbonylation CH3OH + CO CH3COOH old catalyst: Co2(CO)8 at 475 - 600 atm and 210 - 250 C giving a yield of about 85 % new catalyst: Rh(CO)2I2 complex and HI, developed by Monsanto Co. at 15 atm and 175 C, yield was improv

9、ed to more than 95 ,2.3 Enzyme catalysis,The study of the kinetics of enzyme catalyzed reaction is still in its infancy. Very little is known about the mechanism. Main features specificity. For example, Urease will only catalyze the hydrolysis of urea in a very narrow pH and temperature region. high

10、 efficiency mild reaction condition: room temperature 60 C, near neutral condition pH 7,High efficiency,decomposition of H2O2 at 22 C catalyst k L/mols Ea KJ/mol none 10-7 73.2 Fe2+ 56.0 42.3 catalase 3.5107 7.1 Structure of enzymes proteins such as polymer of -amino acid NH2CHR-CO-(NH-CRH-CO-)n NH-

11、CRH-COOH,2.3.1 Reaction kinetics of enzyme catalysis,Influence of enzyme and substrate concentration: At low substrate concentration, the reactions normally show first order with respect to substrate. While at high substrate concentration the rate often tends to a limiting value which is independent

12、 of substrate concentration zero-th order kinetics,2.3.1 Reaction kinetics of enzyme catalysis,Michaelis mechanism k1 k2 E + S ES E + P k-1 using steady state approximation to complex ES dES/dt = k1 ES - k-1ES - k2 ES = 0 ES + E = Eo ES = k1EoS / (k-1 + k2 + k1S) Then we have the reaction rate: r =

13、dP / dt = k2ES = k2k1EoS / (k-1+k2+k1S) = k2EoS / (km+S) here km = (k-1+k2)/k1 is called as Michaelis constant,2.3.1 Reaction kinetics of enzyme catalysis,r = k2EoS / (km+S) At low substrate concentration S kmr = rmax = k2Eo zeroth order kinetics,2.3.1 Reaction kinetics of enzyme catalysis,Physical

14、meaning of Michaelis constant r = rmax S / (km + S) when S = km get r = rmax / 2 when reaction rate reaches a half of maximum, the concentration of substrate equals Michaelis constant,reaction rate r vs substrate concentration s,rmax rmax/2 km S,2.3.1 Reaction kinetics of enzyme catalysis,Evaluation

15、 of km and k2 by reciprocal form r = rmax S / (km + S) 1/r = km / rmax1/S + 1/rmax Lineweaver-Burk plot: 1/r vs 1/S km = slope / intercept, k2Eo = 1 / intercept also the intercept with X axis is -1/km,Lineweaver-Burk plot,1/r slope = Km/rmax 1/rmax 1/S 1/Km 1/r = km / rmax1/S + 1/rmax,2.3.2 Inhibite

16、d enzyme catalyzed reaction,The existence of some impurity can inhibit catalytic activity and decrease the reaction rate. Competitive inhibition: the inhibitor and substrate competitively combine with enzyme in catalyzed reaction,2.3.2 Inhibited enzyme catalyzed reaction,Mechanism KS k2 E + S ES E +

17、 P KI E + I EI whereKS = ES / ES km KI = EI / EI are equilibrium constants and Eo = E + ES + EI Same as above using steady state approximation to complex ES, then we have r = rmax S / (KS(1 + I/KI) + S) 1/r = KS(1 + I/KI) / rmax 1/S + 1/rmax,2.3.2 Inhibited enzyme catalyzed reaction,Difference of th

18、e rate equations Normal enzyme reaction Inhibited enzyme reaction,2.3.2 Inhibited enzyme catalyzed reaction,Since km = (k-1+k2)/k1 KS = ES / ES = k-1/k1 km In Lineweaver-Burk plot, for normal reaction Slope = km / rmax for inhibited reaction Slope = KS(1 + I/KI) / rmax km slope is increased approxim

19、ately (1+I/KI) times,Lineweaver-Burk plot,1/r slope = Ks(1+I/KI)/rmax slope = Km/rmax 1/rmax 1/S 1/Km,2.3.2 Inhibited enzyme catalyzed reaction,The inhibition effects have other kinds of forms such as non-competitive inhibition and anti-competitive inhibition. Non-competitive inhibition: the inhibit

20、or can combine with the intermediate ES as well as combine with enzyme. Anti-competitive inhibition: the inhibitor can only combine with the intermediate ES but without enzyme,2.3.2 Inhibited enzyme catalyzed reaction,Normal enzyme reaction k1 k2 E + S ES E + P k-1 Inhibited reaction KS k2 E + S ES

21、E + P KI E + I EI,2.3.2 Inhibited enzyme catalyzed reaction,Anti-competitive inhibition KS k2 E + S ES E + P KI ES + I ESI Non-competitive Inhibition KS k2 E + S ES E + P KI E + I EI KI ES + I ESI KS EI + S EI,2.3.3 Influence of pH value,Generally, there exists an optimum pH value which is correspon

22、ding to the highest reaction rate. Very often, the optimum value is pH 7 (neutral). The basic idea is that the active centers of the enzyme, especially these contain amino-acid structures, can exist in three forms of ionization. For example: NH3+-COOH NH3+-COO- NH2 -COO protonated form neutral form

23、deprotonated form,2.3.3 Influence of pH value,Generally, there exists an optimum pH value which is corresponding to the highest reaction rate. Very often, the optimum value is pH 7 (neutral). The basic idea is that the active centers of the enzyme, especially these contain amino-acid structures, can

24、 exist in three forms of ionization. For example: NH3+-COOH NH3+-COO- NH2 -COO protonated form neutral form deprotonated form acidic case basic case,2.3.3 Influence of pH value,the three forms of enzyme are in equilibrium and each of them can react with the substrate. it is postulated that only the

25、neutral form EHS can yield products. In the acidic (or basic) condition, the equilibrium moves towards to the complex EH2S (or ES) which yields little products. This can qualitatively explain why the reaction rate is optimum at pH value around 7,2.3.3 Influence of pH value,K1 K2 EH2 EH E K3 k-1| k1 K4 EH2S EHS ES k2 | | EH + product,2.3.3 Influence of temperature,There is no sim