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 H
H H
Catalyst surface

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

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

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

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

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