Catalytic Converters

The number of vehicles has grown significantly over the last decade . Owning a vehicle has become a status symbol. The roads in the cities remain flooded with the vehicles 24×7. The trend shows that these numbers would further shoot up exponentially in near future. The increasing number of vehicles is causing huge  amount of vehicle smoke to be produced. This smoke is one of the most important sources of air pollution. The vehicle exhaust contains toxic pollutants such as Carbon monoxide (CO) , Nitrogen oxides (NOx) and Hydrocarbons (HC). These gases are toxic in nature and are responsible for various diseases in human and animals. In this post we will discuss about a vehicle component which helps in reducing the toxic contents of vehicles exhaust.

The Catalytic converter

As the name suggests this device converts the toxic gases from vehicle's exhaust to the less toxic ones. The catalytic converters catalyse the reactions which convert the poisonous gases in vehicle's exhaust to some other gases which are non poisonous in nature. This device has platinum, palladium and Rhodium based ceramic blocks. These blocks are porous and has honeycomb structure. These metals are extremely precious and hence the use of them makes the Catalytic Converters very costly components. 

Catalytic Converters are fitted in vehicle exhaust system between exhaust manifold and the muffler. The gases coming out of the exhaust manifold pass throughout them and their harmful contents are reduced significantly. There are two types of catalytic converters 

1. Two way catalytic converters

2. Three way catalytic converters

Two way catalytic converters

The two way catalytic converters act on two harmful gases

1. Carbon monoxide CO

2. Hydrocarbons  HCs

They have only one ceramic block i.e. oxidising block. This block consists Platinum and Palladium based ceramics and has honey comb type structure.  The exhaust gases when passes through this porous block, the following oxidising reactions take place

1) For Carbon monoxide

     CO + O2 -- Co2

2) For Hydrocarbons

     HC + O2 -- H2O + Co2

Both the gases CO and HC get oxidised to CO2 and (CO2 + H2O) respectively. CO2 is  a non toxic gas, although it causes global warming but it is also very essential for plants. Hence in this way the poisonous gases like Carbon monoxide and Hydrocarbons get converted to a non poisonous gas Carbon dioxide. 

Three Way Catalytic Converters

The two way catalytic converters were serving the purpose excellently, but a need was felt for a device which can reduce the level of Nitrous Oxide in exhaust gases. The three way catalytic converters were introduced to solve th purpose. Three term three way means it acts on three gases i.e.

1) Carbon Monoxide

2) Hydrocarbons

3) Nitrogen oxide

The three way catalytic converters have an additional reducing ceramic block fitted just before the oxidising block in its assembly. This additional reducing block is made of Platinum and Rhodium based ceramic materials. While the Oxidising block is again made of Platinum and Palladium based ceramics. The reducing block acts on NOx and reduces it to Nitrogen (N2) which is again a non toxic gas. The Oxidising block has the same function as it had in two way catalytic converters. It oxidises the Carbon Monoxide and Hydrocarbons to Carbon dioxide and water. The reactions taking place in this device are:

At reducing block

NOx -- N2 + O2

At oxidising block

CO + O2 -- Co2

HC + O2 -- H2O + Co2

In this way three way catalytic converters reduces the level of CO, HC and Nox in exhaust gases by converting them to other non toxic gases.