The emission of pollutants from one vehicle is generally low but as the number of vehicles is increasing on the road, the environmental pollutants are also increasing.


    About 35% of CO[1], 30% of HC[1], and 25% percent of NOx[1] produced into the atmosphere is from the transportation sector.


    These pollutants have adverse effects on the environment and human health and can cause health problems like cardiovascular disease and cancer. The emissions from vehicles generally depend upon the air-fuel ratio.

    The control techniques for exhaust gas emissions are engine modifications, fuel pre-treatment, fuel additives, exhaust gas recirculation (EGR), positive crankcase ventilation (PCV), and application of catalytic converters.

    Among these methods,  The catalytic converter is effective and is consistent in reducing noxious tailpipe emissions. Hence, it has been developed for use in trucks, buses, cars, motorcycles, and other construction equipment.


What is a Catalytic converter?


    A catalytic converter is a device that converts more toxic exhaust gas pollutants into less toxic pollutants.

The catalytic converter was invented around 1950 by “Eugène Houdry”



How do catalytic converters work?



The catalytic converter is attached to the exhaust pipe of a car.


    It has a metal casing that contains a ceramic honeycomb. The honeycomb is coated with a mix of platinum (Pt), palladium (Pd), and rhodium (Rh). 




    These noble metals are good at resisting oxidation and corrosion, which means they can stand up to bad weather and all the chemicals released by a car engine.


    The honeycomb structure inside a catalytic converter maximizes the surface area where reactions can take place.


What chemical reactions happen in a catalytic converter?


Catalytic converters use reduction and oxidation (redox) reactions to reduce harmful emissions. 



    Catalytic converters use a reduction catalyst composed of platinum and rhodium. It helps reduce nitrogen oxides by removing nitrogen atoms from nitrogen oxide molecules. This lets the free oxygen form oxygen gas  Then, the nitrogen atoms attached to the catalyst react with each other and this reaction creates nitrogen gas (N2 ). 


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Catalytic converters also use an oxidative catalyst composed of platinum or palladium. It helps reduce hydrocarbons (HC) and carbon monoxide (CO). To start with, carbon monoxide and oxygen combine to form carbon dioxide (CO2). Then, unburnt hydrocarbons and oxygen combine to form carbon dioxide and water. 



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Modern catalytic converters also use oxygen sensors. They’re sometimes called lambda sensors. They control how much extra oxygen gets pumped into the exhaust stream. Maintaining the correct amount of oxygen makes the reduction and oxidation reactions more efficient.