Saturday, June 30, 2001
G O O D  M O T O R I N G


Catalytic converters:
Useful allies in fighting pollution
H.Kishie Singh

A catalyst is an agent or substance that speeds up a chemical reaction without itself undergoing any change.

A catalyst is needed to control the poisonous and polluting gases that the internal combustion engine produces. These polluting gases are thrown out from the outlet port into the manifold, which channels them into the exhaust pipe, through the mufflers and out the tail pipe.

The catalytic converter looks like a muffler and is fit on the exhaust pipe. All gases pass through this. Carbon monoxide (CO), Hydro carbon (HC) and Nitrous oxide (N2O) go in and Carbon dioxide (CO2) and water (H2O) come out. Both CO2 and H2O do not harm the environment. The catalytic converter has oxidised/burned the polluting gases without itself being involved in the reaction.

 


Platinum, palladium, rhodium, or a mixture of all three is used in a converter. These materials build up extreme heat, up to 800°C, ignite the polluting gas and turn it into harmless vapour.

Catalytic converters are of various types:

Mini catalytic converter: As the name implies, it is small in size and can be placed close to the engine — the heat source. It heats up rapidly when the engine warms up to minimise polluting emissions. A mini converter is usually used together with a larger converter.

Monolithic-type converter uses small ceramic beads as catalyst.

Two-way catalytic converter is also known as an oxidation-type converter. This reduces only HC only CO emissions. Platinum is usually used in this converter.

Three-way catalytic converter is also known as a reduction converter. This converter reduces emissions of HC, CO and N2O. A three-way converter uses rhodium and platinum as catalyst.

Then there is a dual bed converter. This consists of two separate units, a two-way and a three-way converter, in a simple housing. It also has a mixing chamber. The exhaust gases are forced into this and help to burn harmful emissions.

All catalytic converters have to have the exhaust gases forced through the micro-millimetre holes in the ceramic tile or beads or whatever the manufacturer specifies for a particular engine.

Since there is no free flow of exhaust gases as they have to be forced through the catalytic converter, there is a definite loss of power to the engine.

A catalytic converter needs no maintenance and will last for years and thousands of kilometres. However only unleaded petrol can be used in a vehicle fitted with a catalytic converter. One tank full of the wrong fuel and the catalytic converter can be rendered useless.

Happy Motoring!