Question

Why is it desirable to use unleaded petrol in vehicles fitted with a catalytic converter?

Answer 1

Air pollution; pollutants may travel long distances in the air spoiling the environment far away from the sources of emission.
There are three steps that can be taken to reduce air pollution: separation of pollutants from harmless gases, avoidance of pollutants, and conversion of pollution to harmless materials.
The catalytic converters are devices used to control air pollution.

Complete answer: Catalytic converters are the devices having expensive metals examples – platinum-palladium and rhodium as the catalyst.
Catalytic converters are fitted into automobiles for reducing the emission of gases.
As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted to carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas respectively.
Vehicles fitted with catalytic converters should run on unleaded petrol would inactivate the catalyst in the converter. Leads can quickly deposit onto the converter thereby poisoning the catalyst.
As a result in a very short time, the catalyst will be of no use. The unleaded petrol does not have the lead compound because of unleaded petrol is used in vehicles fitted with a catalytic converter.

Note: There are many other ways to control particulate matter which include arresters.
These are the control devices to separate particulate pollutants.
Arresters are of various types: Control equipment such as gravity settling tanks or porous filtrates, electrostatic precipitators, cyclonic separators and trajectory separators installed in the factories can minimize air pollution.