Why is the use of unleaded petrol recommended for motor vehicles equipped with catalytic converters?

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Hint: The exhaust system of a motor vehicle comprises a device that contains catalysts for the conversion of pollutant gases into non-harmful gases. This device is termed a catalytic converter. Unleaded petrol simply means petrol devoid of lead. Lead is responsible for the inactivation of catalysts.

Complete answer:The burning of gases in the exhaust of a motor vehicle produces harmful and toxic gases like carbon monoxide, Nitrogen oxide, Ammonia, Sulphur dioxide, etc. all these pollutant gases enter the atmosphere and cause harm to the environment. The released burnt fuel by-products are of utmost concern. The use of non-eco-friendly vehicles should be avoided. The particulate matter released from these vehicles makes up smog and causes acid rain, ozone hole, and many harming phenomena.
As an alternating solution to the harmful petrol burning in exhausts of vehicles, the catalytic converters were introduced. The catalytic converters are devices that contain expensive catalysts like rhodium and platinum-palladium. These catalysts speed up the burning reactions of petrol and convert harmful gases into non-toxic gases. For example, hydrocarbons are converted into carbon dioxide and water, carbon monoxide into carbon dioxide, and nitric oxide into nitrogen. Thus, they are useful in controlling vehicle pollution. But one of the major issues is the inactivation of these expensive metals by lead present in petrol. To overcome this issue unleaded petrol was introduced. The unleaded petrol enhanced the activity of these catalysts and thus vehicle pollution is controlled.

Note: The main difference between unleaded and leaded petrol is the presence of an additive called tetraethyl lead. The additive was first introduced to eliminate the knocking of the engine. It was found later that lead has some serious side-effects and thus needs to be eliminated itself.