how are heterogeneous catalysts used to reduce levels of air pollution from vehicles? please help =D?

Answer 1

During combustion of a vehicle engine, harmful gases are produced (such as carbon monoxide and hydro carbons, produced by burnt petrol.) There for a catalyst (which is in the stream line of an exhaust), is specially lined with a precious metal which burns the fuel in to less harmful gases (but its still not 100% efficient)

There is a sensor before the catalyst called a lamda sensor which controls the air/fuel ratio. During this the heat from the exhaust gases heats up the catalyst to almost glowing point. This is what causes the gases to burn.

99% of cars manufactured after 1992 where fitted with heterogeneous catalysts.

Answer 2

They can be used to catalyse a further oxidation reaction to remove the products of incomplete combustion such as soot, polyaromatic hydrocarbons, carbon monoxide and unburnt fuel (hydrocarbons). The products of these reactions are carbon dioxide and water.

They can also be used to reduce NOx and SOx via a range of reactions that will produce nitrogen, oxygen and maybe ammonia or hydrogen sulphide.

There are also a range of intelligent systems that monitor the composition of the exhaust gases (usually oxygen content) and change the fuel:air mix of the engine accordingly to reduce pollution directly and/or help provide the best mix of gases to the catalysts to allow them to work most effectively.

Answer 3

Incomplete combustion of the fuel produces carbon monoxide, which is toxic. The electric spark and high temperatures also allow oxygen and nitrogen to react and form nitric oxide and nitrogen dioxide, which are responsible for photochemical smog and acid rain. Catalytic converters reduce such emissions by adsorbing CO and NO onto catalytic surface, where the gases undergo a redox reaction. Carbon dioxide and nitrogen are desorbed from the surface and emitted as relatively harmless gases:

Answer 4

So the main pollutants created are:
CO from fuel which is not fully burnt
NO(X)- nitrogen oxides which produce smog and are
HC- unburnt hydrocarbons
some sulphur compounds

Co2 is also produced by cars but is not considered a true pollutant as it is not directly damaging to our health although it is a gren house gas.

A catalytic convertor is a sort of honeycomb structure which contains small particles of Palladium and rhodium which are expensive metals which is why catalytic convertors cost so much.

These metal particles act as the heterogenous catalysts.

Carbon monoxide is converted to CO2
2CO + O2 → 2CO2

Unburnt hydrocarbons are converted to co2 and water
2CxHy + (2x+y/2)O2 → 2xCO2 + yH2O

Nitrogen oxides are converted to oxygen and nitrogen
2NOx → xO2 + N2