Industrial Catalysis

Controlling exhaust emissions with catalytic converters

There is world wide concern about the emissions from motor vehicles. One attempt to minimise this problem has been the introduction of catalytic converters in car exhaust systems.

Summary of conditions for catalytic converters

temperature

424K

catalyst

platinum/rhodium alloy spread over a ceramic honeycomb type of support

conversion

 

almost complete

The catalyst speeds up reactions within the exhaust system that remove carbon monoxide, unburnt hydrocarbons and oxides of nitrogen.

Reactions

a)

carbon monoxide

 

2CO + O2

2CO2

 

 

 

 

 

 

 

b)

heptane

 

C7H16 + 11O2

7CO2 + 8H2O

 

 

 

 

 

 

 

c)

reduction of
nitric oxide

 

2NO + 2CO

N2 + 2CO2

 

 

 

More on the catalyst

The catalyst is a platinum/rhodium alloy spread over a ceramic honeycomb type of support. It is used in this form because:

  • a platinum catalyst alone would not start working until around 513K, when alloyed with rhodium it starts working at about 424K
  • the honeycomb structure means that the surface of catalyst exposed to the exhaust gases is about the same as two football pitches
Fitting a catalytic converter.
Cut away catalytic converter showing the honeycomb catalyst inside.