#ReducingTheEffectsOfNitrogenOxides

#Chemistry

#ChemistryOfTheEnvironment

Oxides of nitrogen

• These compounds (NO and NO2) are formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces

• Exhaust gases also contain unburned hydrocarbons and carbon monoxide

• Cars are fitted with catalytic converters which form a part of their exhaust systems

• Their function is to render these exhaust gases harmless

Catalytic converters

• They contain a series of transition metal catalysts including platinum and rhodium

• The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction

• A series of redox reactions occurs which neutralises the pollutant gases

• Carbon monoxide is oxidised to carbon dioxide:

2CO + O2 → 2CO2

• Oxides of nitrogen are reduced to N2 gas:

2NO → N2 + O2

2NO2 → N2 + 2O2

• A single reaction can summarise the reaction of nitrogen monoxide and carbon monoxide within a catalytic convertor:

2NO + 2CO → N2 + 2CO2

• Unburned hydrocarbons can also be oxidised to carbon dioxide and water:

C8H18 + 12½O2 → 8CO2 + 9H2O