Catalysts
Catalyst
A catalyst increases the rate of reaction by providing an alternative
reaction pathway lowering the activation energy. They are economically
important and allow chemicals to be formed cheaper, faster and safer.
A Maxwell-Boltzmann distribution showing the effect of a catalyst
Types of catalysts
Homogeneous
Catalysts in the same phase (same physical state) as the reactants and
products.
Examples:
Examples
Esterification
Hot concentrated sulphuric acid catalyst
Break down of ozone
Cl• catalyst The breakdown of ozone can lead to increased risks
of skin cancers due to a lack of protection from UV light
Cl• formation from chloro-fluoro carbons (CFCs)
Reaction stages
Heterogeneous
Catalysts in a different phase as the reactants and products (different physical state, usually a solid).
These react of a series of steps:
1. Adsobtions (not absorption) of gaseous molecules to the catalyst surface
2. Reaction – bonds weakened on the catalyst surface lowering the
activation energy
3. Desorption of product molecule from surface
Examples
· Haber process with an iron catalyst – used to make ammonia for fertilisers
N2 + 3H2 
2NH3
· Isomerisation of petrol with a platinum catalyst
· Hydrogenation of vegetable oils to manufacture margarine with a nickel catalyst
CH2=CH2 + H2
CH3CH3
Car exhausts
Catalytic converters include platinum and rhodium catalysts. They are used to remove toxic carbon monoxide which is formed from the incomplete combustion of petrol, oxides of nitrogen which can lead to acid rain formed from nitrogen and oxygen reacting from the air and unburnt hydrocarbons which can lead to photochemical smog and low-level ozone.
Reaction
2NO + 2CO 2CO2
+ N2