CatalysisCatalyzedathin layerofReactive sitesonsolidcatalystsupportedsurfaceoftendblockoncheapercarrierelementorcompoundwithmaterialdelectronsororbitalsforboncingtoreactantEEaloweredto32kJmol-1withplatinum catalyst26kJmol-1Other important examples:V,Q, in the Contact processIron in Haber processPlatinum in the oxidation of ammonia and in car exhaust systems
16 Catalysis Catalyzed Other important examples: V2O5 in the Contact process Iron in Haber process Platinum in the oxidation of ammonia and in car exhaust systems
CatalysisHOMOGENEOUS CATALYSISHere the catalyst and the reactants are in the same phase.The catalyst:omight provide a more reactiveattacking speciese.g. CN- in the carbonyl reaction with hydrogen cyanide or thehydroxide ion in the hydrolysis of estersCN-8 better nucleophile and more reactive thanH-C-NO?HQe1better nucleophile and more reactive than water0QO-HHomight enhance the reactive sitee.g. addition of acid in the reaction between ethanol and bromidemore electron deficientcarbonmadeionsCH30-8HCHHGHBr9-?HHH-17betterleavinggroupmade
17 Catalysis HOMOGENEOUS CATALYSIS Here the catalyst and the reactants are in the same phase. The catalyst: ●might provide a more reactive attacking species e.g. CNin the carbonyl reaction with hydrogen cyanide or the hydroxide ion in the hydrolysis of esters better nucleophile and more reactive than better nucleophile and more reactive than water ●might enhance the reactive site e.g. addition of acid in the reaction between ethanol and bromide ions
Catalysismight be able to react with both reactants through having arange of reactive oxidation statese.g. the reaction between peroxydisulphate (VD) and iodide iscatalyzed by both iron (I) and iron (Il)S2O.2-+21→2SO,2-+12slowreactionbetweennegative ionsiron(l)reactswithrapidperoxydisulphatereactions2Fe2++S2O2-→2SO.2-+Fe3+过氧二硫酸根betweenoppositelyiron(ll)reactswithchargediodideions2Fe3++21-→2Fe2++12ions连二亚硫酸发dithionousacid；连二亚硫酸盐 dithionite S,O.2Na2S204，保险品18
18 Catalysis ● might be able to react with both reactants through having a range of reactive oxidation states e.g. the reaction between peroxydisulphate (VI) and iodide is catalyzed by both iron (II) and iron (III) 连二亚硫酸 dithionous acid; 连二亚硫酸盐 dithionite S2O4 2- Na2S2O4 , 保险品 过氧二硫酸根
CatalysisEnzymesMany complex protein molecules have reactive sites that allowreactants to be absorbed onto the surface of the protein because ofthe way the molecular chains are folded.This lowers the activationenergy of bond breaking. Enzymes are usually very specificcatalysts, i.e. each enzyme only catalyses one particular reaction.2H,02→ 2H,0+ 0275.3Activation energy in kJ mot!48.9with platinum23withenzymecatalase（过氧化氢酶）酶IPt催化剂无75~59~50~25E,/kJ.mol-1k催化/k非催化16115X10822500(T=300 K)19
19 Catalysis Many complex protein molecules have reactive sites that allow reactants to be absorbed onto the surface of the protein because of the way the molecular chains are folded. This lowers the activation energy of bond breaking. Enzymes are usually very specific catalysts, i.e. each enzyme only catalyses one particular reaction. Enzymes 5×108 1 611 22500 k催化/k非催化 （T=300 K） Ea /kJ.mol 75 ~59 ~50 ~25 -1 催化剂 无 I－ Pt 酶 Activation energy in kJ mol-1 75.3 with platinum 48.9 with enzyme catalase（过氧化氢酶） 23 2H2O2 → 2H2O + O2