6.2.4 Catalytic Converters

Exhaust fumes major source of pollution CO [poisonous] NO [forms acid rain / poisonous] NO2 [forms acid rain / poisonous] [Oxides of nitrogen often referred to as NOx] Unburned hydrocarbons e.g. C2H4 [poisonous / carcinogenic / form smog] Need to reduce pollution as much as possible Catalytic converter changes these into harmless gasses [ CO2, H2O and N2] Compulsory since 1993

Looks just like any other silencer box

Removal of Pollutants CO reacts with oxides of nitrogen to form CO2 and N2 CO + NOx = CO2 + N2 Umburned hydrocarbons react with oxides of nitrogen to form CO2, N2 and H2O C2H4 + NOx = CO2 + H2O + N2

CO + NOx = CO2 + N2 C2H4 + NOx = CO2 + H2O + N2 CO2 N2 H2O Pt, Pd, Rh Catalysts Pollutants NO NO2 CO Cross-section C2H4

Calalysts are Pt, Pd, Rh Coated on a ceramic honeycomb to give large surface area [2-3 soccer pitches] Good example of heterogeneous catalysis [ i.e. reactants and catalyst in different states] Work best at high temperatures [300oC]

Destruction of Converter Last about 50000 miles Ceramic breaks down due to high temperature and vibration Catalysts Poisoned by Pb and other heavy metals Using leaded petrol destroys catalysts at once Most of the catalysts can be recovered

Catalytic Converters Reduce Pollution Acid rain Photochemical smog