CI 10'4

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

Catalyst surface
5

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

H H C CH
H
H H

6

• Bonds within reactant molecules are weakened and
  break

7

• New bonds form between the reactants

H H

8

• New bonds form between the reactant molecules

H
9

• The product(s) leave the catalyst surface

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