ITK-329 Kinetika & Katalisis

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

2. Most chemical processes use catalyst at some stage in production process 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. • Catalyst: • Selectively enhances the rate of a reaction • Changes the reaction pathway • Neither consumed nor formed • Does not affect equilibrium

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

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

5. How Catalysts Work

6. 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 [(CH3)2C(CN)N]2

7. How Catalysts Work (cont’):Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst Acid catalysts: CH3CH2HC=CH2 CH3HC=CHCH3

8. O NH2CNH2 + HOH 2NH3 + CO2 How Catalysts Work (cont’):Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst Enzymatic Reactions:

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

10. How Catalysts Work (cont’):Intermediate Stabilization Reactant + Catalyst  Stable Complex  Products + Catalyst On solid Pt(111) catalysts:108 enhancement factor Gas phase, no catalyst:

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

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

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

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

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

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