1. CI 10.4 What is a catalyst?

2. Catalysts Speed up the rate of a chemical reaction Are not chemically changed or used up in the reaction May be specific for a particular reaction – applies especially to enzymes in biological reactions

3. Types of catalysts Homogeneous catalysts – reactants and catalyst in same state Heterogeneous catalysts – reactants and catalysts in different states

4. How do heterogeneous catalysts work? Catalyst is usually a solid H H C C H H H Catalyst surface H

5. H H C C H H H Reactants are adsorbed onto catalyst surface- i.e. weak bonds formed between reactants and catalysts H

6. Bonds within reactant molecules are weakened and break H H C C H H H

7. New bonds form between the reactants H H C C H H H

8. H H H C C H H New bonds form between the reactant molecules H H

9. The product(s) leave the catalyst surface H H C C H H H H H H

10. Catalyst poisoning In heterogeneous catalysis Catalyst poisoned by a chemical binding to surface Poison bonds irreversibly with catalyst Sulphur and lead are two examples of catalyst poisons

11. Cleaning a catalyst Catalysts can sometimes be regenerated by blowing hot air over catalyst – oxidises chemicals on surface Used to remove carbon (soot) after catalytic cracking