Catalytic Converters Flashcards
What gases do exhaust fumes contain?
Carbon monoxide CO
Nitrogen monoxide NO
Unburned hydrocarbons
What are unburned hydrocarbons?
These are compounds containing carbon and hydrogen
Where does CO come from?
The incomplete combustion of hydrocarbons in fuel
What are the oxides of nitrogen in exhaust fumes referred to as?
NO compounds
What are commonly referred to as NO compounds?
Oxides of nitrogen in exhaust fumes
How are oxides of nitrogen formed?
When any fuel is burned in air at high temperatures part of the nitrogen in the air is oxidised to become nitrogen monoxide
What does nitrogen monoxide react with to form nitrogen dioxide?
Oxygen
How is nitrogen dioxide formed?
When nitrogen monoxide reacts with oxygen
What used to be emitted from exhaust fumes when leaded petrol was used?
Lead compounds
Why are lead compounds no longer emitted from exhaust fumes?
As leaded petrol is no longer used
Where do unburned hydrocarbons come from?
When some fuel is not burned in the engine hydrocarbons are emitted into the exhaust fumes
Describe carbon monoxide
A colourless, odourless and tasteless gas that is highly poisonous
Describe the oxides of nitrogen.
They are poisonous and contribute to acid rain
What do unburned hydrocarbons give rise to?
Smog
Define a catalytic converter
A device in the exhaust system of a motor vehicle which contains catalysts to convert pollutants in the exhaust gases to less harmful substances
Describe the structure of a catalytic converter
2 main points
A catalytic converter consists of a thin coating of platinum, palladium and rhodium (the catalysts) on a ceramic or metal ‘honeycomb’ inside a stainless steel case
The catalysts are spread over the surface of the honeycomb giving them a huge surface area
What is the main reaction that happens in the catalytic converter?
The reaction between the polluting gases themselves (CO and NO) to form carbon dioxide and nitrogen
What do the unburned hydrocarbons react with in a catalytic converter?
The nitrogen oxides
What is formed when the unburned hydrocarbons react with the nitrogen oxides in a catalytic converter?
Nitrogen and water
What are the three reactants used in a catalytic converter?
Carbon monoxide
Nitrogen monoxide
Hydrocarbons
What are the three products of a catalytic converter?
Carbon dioxide
Nitrogen
Carbon dioxide and water
What type of catalysis takes place in a catalytic converter?
Heterogeneous catalysis
Why do catalytic converters have to be replaced sometimes?
2 reasons
As a result of poisoning of the catalysts
Disintegration of the catalysts and the ceramic surfaces as a result of vibration and wear from fast moving hot gases
Comment on the life of a catalytic converted in a car where leaded petrol is used.
The catalytic converter will have a very short life as the lead will poison the catalysts
Define a catalyst poison
A substance that makes a catalyst inactive
What compound is more strongly adsorbed to the surface of the catalysts then any other compound in a leaded petrol vehicle?
Lead
When changing a catalytic converter, does everything need to be replaced?
No as it is possible to recover most of the catalysts and recycle them
