Question

Question C3 (3 42 2+ 2 = 13 marks) The catalytic converter is an essential component of all modern motor vehicles Illustrate the structure of the monolithic catalyst and briefly describe the purpose of each layer Identify the catalytically active metals generally employed and describe their function in chemical terms. (a) What is the air-fuel ratio and why is it important? (b) (c) What is the temperature range for efficient operation? What happens when the temperature is too hot or too cold? Over recent years, an extra function has been added to the catalytic converters for diesel trucks. What does this added function achieve and how does it work? (d)

Answer 1

a.) Catalytic converter is a stainless steel box having alumina inside in the form of honeycomb.

It has following catalytic agent for conversion of pollutants to harmless gases :-

Platinum - used to convert HC to CO2 & H2O

Palladium - convert CO to CO2

Rhodium - Convert NOx to N2 & O2

b. ) Air fuel ratio is the amount of air used for the combustion of fuel.

Fuel + O2 ---> CO2 + H2O

When the combustion of air & fuel takes place in such a manner that there is no free oxygen left nor is fuel remaining in any other form after combustion, the Air Fuel ratio is called stoichiometric Air - Fuel ratio.

It is important because this ratio decides the temperature of the charge. The temperature of charge is responsible for knocking & detonation. If temperature is less it is good for petrol engine whereas high temperature is desirable in diesel engine.

C.) For efficient working it's temperature range is above 200°c to 600°c

During cold car burns more fuel this decreases the efficiency of catalytic converter.

Due to high temperature there is possibility of mechanical damage to the catalytic converter as it's components are metallic they too have there melting point and refractoriness.

d.) Extra function added to them is to reduce the emission of Sulphur and lead, they have improved there efficiency and working temperature limit. They are now using layered formulations.