8 10.5 Catalytic reactions Catalyzed reactions Out-class extensive reading Levine, p.577 17.16 Catalysis 1717 Enzyme catalysis
§10.5 Catalytic reactions Catalyzed reactions Out-class extensive reading: Levine, p.577 17.16 Catalysis 17.17 Enzyme catalysis
10.5 Catalytic reactions 414催化化学 知识点: 1)催化剂催化作用催化反应特征助催化剂催化剂载体催化剂的选择性催化活性 抑制剂*转换频率(tum- over frecμ uency)催化剂中毒催化剂再生自催化*化学振荡 (2)均相催化酸碱催化布朗斯特( Bronsted)定律配位催化 (3)多相催化催化活性位表面反应速率表面反应历程朗缪尔-里迪尔( Langmuir- Idea) 机理朗缪尔-欣谢尔伍德( Langmuir- Hinshelwood)机理 (4)酶酶催化底物米氏( Michaelis- Menten)机理米氏方程米氏常数竞争性抑制 (5)光催化电催化光电催化 能力:(1)能够说明均相催化、多相催化、酶催化的一般机理,推导相关动力学方程,进行相 关计算和讨论;(2)能够从机理角度说明催化反应的动力学特征。 素质:(1)能够概括和分析催化剂和催化反应的主要特征:(2)能够从微观角度说明催化剂中毒 的机制和再生的原理和方法;(3)能够从结构与性能关系的角度,说明酶催化的特异性以及反应机 理多样性的原因;(4)能够从热力学角度说明化学吸附强度与催化活性的关系
10.5 Catalytic reactions
10.5 Catalytic reactions 5.1 Catalysts and catalysis Cataly Catalyst a substance that can increase the rate of The phenomenon of acceleration or a chemical reaction without changing the retardation of the rate of a chemical total gibbs free energy reaction by addition of small amount of foreign substances to the reaction system Catalyst: Pt-Rh all Catalyzed reaction 4NH, +50=4NO +6HO
5.1 Catalysts and catalysis Catalyst A substance that can increase the rate of a chemical reaction without changing the total Gibbs free energy. Catalysis The phenomenon of acceleration or retardation of the rate of a chemical reaction by addition of small amount of foreign substances to the reaction system. 10.5 Catalytic reactions Catalyst: Pt-Rh alloy Catalyzed reaction: 4NH3 + 5O2 = 4NO + 6H2O
10.5 Catalytic reactions 5.1 Catalysts and catalysis 大亭化季 Uni: Chem. 2020, 35( 0009 知识介绍 doi:10.3866 PKU.DXHX202002046 www.dxhx.pku.edu.cn 催化剂相关概念的辨析 凌晨,张树永 山东大学化学与化工学院,济南250100 IUPAC A substance that increases the rate of a reaction without modifying the overall standard gibbs energy change in the reaction; the process is called catalysis. The catalyst is both a reactant and product of the reaction
5.1 Catalysts and catalysis 10.5 Catalytic reactions IUPAC: A substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction; the process is called catalysis. The catalyst is both a reactant and product of the reaction
10.5 Catalytic reactions 5.1 Catalysts and catalysis 表1主要教材和专著给出的催化剂定义和特征分析的比较 用量速度质量数量化学性质参与反应反应途径活化能化学平衡反应物条件计量关系文献 改变 不变 不变 改变 改变△G不变 改变 不变 不变 参与 改变 改变 不变 条件 改变 不变 不变 参与 改变 降低 不变 条件 [7 少量加快 不变 不变 任意 不变 不变 参与 改变 降低 △G不变 条件 不存在 加快 不变 改变 降低 加快 不变 加快不消耗 加速 参与 △G不变 反应物 带底色的是催化反应特征而非定义内容 NEW DEFINITION: A substance that alter the reaction pathway and increases the rate of a reaction without modifying the overall standard Gibbs energy change of the reaction
5.1 Catalysts and catalysis 10.5 Catalytic reactions NEW DEFINITION：A substance that alter the reaction pathway and increases the rate of a reaction without modifying the overall standard Gibbs energy change of the reaction
10.5 Catalytic reactions 5.2 type of catalysis ypes Definition Examples )Homogeneous The catalyst is present Hydrolysis of sucrose with inorga in the same phase as acid catalysis the reactant NO2 catalyzes the oxidation of so2 2)Heterogeneous The catalyst constitutes Haber s process for ammonia synthesis catalysis a separate phase from contact oxidation of sulphur dioxide the reaction system ydrogenation of alkene, aldehyde, etc Reaction catalyzed 3)Biological/ Hydrolysis of starch in stomach with with biological enzyme catalysis the aid of diastase catalysts: enzyme
5.2 type of catalysis Types Definition Examples 1) Homogeneous catalysis The catalyst is present in the same phase as the reactant. Hydrolysis of sucrose with inorganic acid. NO2 catalyzes the oxidation of SO2 2) Heterogeneous catalysis The catalyst constitutes a separate phase from the reaction system Haber’s process for ammonia synthesis; contact oxidation of sulphur dioxide; Hydrogenation of alkene, aldehyde, etc. 3) Biological / enzyme catalysis Reaction catalyzed with biological catalysts: enzyme Hydrolysis of starch in stomach with the aid of diastase 10.5 Catalytic reactions
10.5 Catalytic reactions 5.3 General characteristics of catalyzed reactions 1)Catalyst takes part in the reaction (CH3)3COH-)(CH3)2C=CH2+H2o without catalyst: k=4.8 x 10 4 exp(-32700/msI with HBr(g) as catalyst: k=9.2 x 10 2 exp(-15200/T)dm3 mol-ls-I 15200 92×102expl k 32700)41×103 48×104exp T
5.3 General characteristics of catalyzed reactions 1) Catalyst takes part in the reaction. (CH3 ) 3COH ⎯→ (CH3 ) 2C=CH2 + H2O without catalyst: k = 4.8 1014 exp(-32700/T) s -1 with HBr (g) as catalyst: kc = 9.2 1012 exp(-15200/T) dm3 mol-1 s -1 23 14 12 4.1 10 32700 4.8 10 exp 15200 9.2 10 exp = − − = T T k kc 10.5 Catalytic reactions
10.5 Catalytic reactions with HBr serving as catalyst: A+c A-C 1)t-Bu-OH+ HBr t-Bu-Br+H2O 2)t-Bu-Br->(CH3)2C=CH2 HBr A-C+b-k2A-B+C hkAb kAlB A B k E.,+E a.2 E A B c By altering reaction path, catalyst can lower A+B+C activation energy of the overall reaction AC+B significantly and change the reaction rate dramatically
with HBr serving as catalyst: 1 2 1 [A][B] [A][B] k k r k k− = = Ea,app = Ea,1 + Ea,2 − Ea,−1 By altering reaction path, catalyst can lower activation energy of the overall reaction significantly and change the reaction rate dramatically. 1 1 2 A C A C A C + B A B + C k k k − + − − ⎯⎯→ − 10.5 Catalytic reactions
10.5 Catalytic reactions 2) No impact on the thermodynamic features of the reaction (1) Catalyst cannot start or initiate a thermodynamically non-spontaneous reaction (2)Catalyst can change the rate constant of forward reaction and backward reaction with the same amplitude and does not alter the final equilibrium position x Catalyst can only shorten the time for (k, +k_)t= kt (x-x) reaching equilibrium (3)Catalyst is effective both for forward reaction and backward reaction 2NH3、N2+3H Study on the catalyst for formation of ammonia can be done with easy by making use of the decomposition of ammonia
2) No impact on the thermodynamic features of the reaction (1) Catalyst cannot start or initiate a thermodynamically non-spontaneous reaction; (2) Catalyst can change the rate constant of forward reaction and backward reaction with the same amplitude and does not alter the final equilibrium position. Catalyst can only shorten the time for reaching equilibrium. e e ln ( ) ( ) x k k t kt x x = + = + − − (3) Catalyst is effective both for forward reaction and backward reaction. Study on the catalyst for formation of ammonia can be done with easy by making use of the decomposition of ammonia. cat. 3 2 2 2NH N 3H + 10.5 Catalytic reactions
10.5 Catalytic reactions 3)Selectivity of catalysts (1) The action of catalyst is specific. Different reaction calls for different catalyst Hydrogenation? Isomerization through carbonium? (2)The same reactants can produce different products over different catalysts CH,=CH,+ CH2—CH2 2 200~3009C O PdCl- CuCl CH,=CH,+ CH3—C、 200~3000C H
3) Selectivity of catalysts (1) The action of catalyst is specific. Different reaction calls for different catalyst. Hydrogenation? Isomerization through carbonium? (2) The same reactants can produce different products over different catalysts. CH2 Ag 200~300 o C CH2 CH2 O + 2 1 CH2 O2 CH2 200~300 o C + 2 1 CH2 O2 PdCl 2 CuCl 2 CH3 C O H 10.5 Catalytic reactions