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A catalyst is a substance which affects
the rate of a chemical reaction without
being chemically changed itself.
Heterogeneous catalyst
The catalyst is in a different phase to the
reactants (eg solid catalyst with liquid
For example
Fe in the Haber process
Ni in margarine production
Pt and Rh in a catalytic converter
Heterogeneous catalysts
The Haber process
Hardening of fats
Incomplete combustion of fuels leads to products
such as CO and NO.
These react in the presence of UV rays (from
sunlight) to produce low level ozone, aldehydes and
PAN (peroxyacetylnitrate CH3CO-OO-NO2)
collectively known as photochemical smog.
Ozone causes breathing difficulties, headaches, fatigue and can aggravate
respiratory problems. PAN can irritate the eyes, causing them to water and sting.
In a catalytic converter, a rhodium
catalyst is used to break NO into
N2 and O2
Homogeneous catalyst
The catalyst is in the same phase as the
For example
Cl radicals in the destruction of ozone
H+ in Esterification
Homogeneous catalysts
• Ozone O3 forms a layer around the
atmosphere which acts as a shield preventing
too much UV radiation from reaching earths
• CFCs decompose in the upper atmosphere
producing chlorine free radicals.
• These radicals act as a catalyst for the
reaction O3 + O
Homogeneous catalysts