1. 88 ITK-329 Kinetika & Katalisis Introduction to Catalyst & Catalysis Dicky Dermawan www.dickydermawan.net78.net dickydermawan@gmail.com Chapter 5

2. 89 Catalyst: Selectively enhances the rate of a reaction Selectively enhances the rate of a reaction Changes the reaction pathway Changes the reaction pathway Neither consumed nor formed Neither consumed nor formed Does not affect equilibrium Does not affect equilibrium Catalyst (Ostwald): A substance one adds to a chemical reaction to tremendously speed up the reaction without the catalyst undergoing a chemical change itself Actually catalysts do undergo chemical changes during the course of reaction. It’s just that the changes are reversible. Most chemical processes use catalyst at some stage in production process

3. 90 Types of Catalysts Homogeneous Catalyst Acids or bases Acids or bases Metal salt Metal salt Enzymes Enzymes Radical initiators Radical initiators Solvents Solvents

4. 91 Types of Catalysts (cont’) Heterogeneous Catalyst High surface area

5. 92 How Catalysts Work

6. 93 How Catalysts Work (cont’) Catalyst can initiate reactions. The mechanisms are similar to the mechanism without a catalyst, but the initiation process is much faster with the catalyst Radical Initiator in polymerization: peroxides ROOR, AIBN [(CH 3 ) 2 C(CN)N] 2

7. 94 How Catalysts Work (cont’): Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst CH 3 CH 2 HC=CH 2 CH 3 HC=CHCH 3 Acid catalysts:

8. 95 How Catalysts Work (cont’): Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst Enzymatic Reactions: O NH 2 CNH 2 + HOH 2NH 3 + CO 2

9. 96 How Catalysts Work (cont’): Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst Metalic cluster catalyst:

10. 97 How Catalysts Work (cont’): Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst On solid Pt(111) catalysts: 10 8 enhancement factor Gas phase, no catalyst:

11. 98 Ethylene hydrogenation to ethane on Ni catalyst Heterogeneous Catalysis = adsorption – (surface) reaction - desorption How Catalysts Work (cont’) Example in Heterogeneous Catalysis

12. 99 Heterogeneous Catalyst Activity: Turnover Number/Turnover Frequency T n = the rate that molecules are converted per active site in the surface of the catalyst per second.

13. 100 How Catalysts Work (cont’): Configuration Dependent Platinum surface structure

14. 101 typically by 19 – 30 kcal/mol, thus… lower the temperature where a reaction takes place How Catalysts Work (cont’) Catalyst lowers the activation barrier for the reaction,

15. 102 Catalytic Kinetics Various & significantly different from those of uncatalyzed kinetics Effect of Concentration/ Pressure

16. 103 Catalytic Kinetics (cont’) Temperature effect: does not obey Arrhenius law