Catalytic Converters

Question 1

What gases do exhaust fumes contain?

Answer 1

Carbon monoxide CO
Nitrogen monoxide NO
Unburned hydrocarbons

Question 2

What are unburned hydrocarbons?

Answer 2

These are compounds containing carbon and hydrogen

Question 3

Where does CO come from?

Answer 3

The incomplete combustion of hydrocarbons in fuel

Question 4

What are the oxides of nitrogen in exhaust fumes referred to as?

Answer 4

NO compounds

Question 5

What are commonly referred to as NO compounds?

Answer 5

Oxides of nitrogen in exhaust fumes

Question 6

How are oxides of nitrogen formed?

Answer 6

When any fuel is burned in air at high temperatures part of the nitrogen in the air is oxidised to become nitrogen monoxide

Question 7

What does nitrogen monoxide react with to form nitrogen dioxide?

Answer 7

Oxygen

Question 8

How is nitrogen dioxide formed?

Answer 8

When nitrogen monoxide reacts with oxygen

Question 9

What used to be emitted from exhaust fumes when leaded petrol was used?

Answer 9

Lead compounds

Question 10

Why are lead compounds no longer emitted from exhaust fumes?

Answer 10

As leaded petrol is no longer used

Question 11

Where do unburned hydrocarbons come from?

Answer 11

When some fuel is not burned in the engine hydrocarbons are emitted into the exhaust fumes

Question 12

Describe carbon monoxide

Answer 12

A colourless, odourless and tasteless gas that is highly poisonous

Question 13

Describe the oxides of nitrogen.

Answer 13

They are poisonous and contribute to acid rain

Question 14

What do unburned hydrocarbons give rise to?

Answer 14

Smog

Question 15

Define a catalytic converter

Answer 15

A device in the exhaust system of a motor vehicle which contains catalysts to convert pollutants in the exhaust gases to less harmful substances

Question 16

Describe the structure of a catalytic converter

2 main points

Answer 16

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

Question 17

What is the main reaction that happens in the catalytic converter?

Answer 17

The reaction between the polluting gases themselves (CO and NO) to form carbon dioxide and nitrogen

Question 18

What do the unburned hydrocarbons react with in a catalytic converter?

Answer 18

The nitrogen oxides

Question 19

What is formed when the unburned hydrocarbons react with the nitrogen oxides in a catalytic converter?

Answer 19

Nitrogen and water

Question 20

What are the three reactants used in a catalytic converter?

Answer 20

Carbon monoxide
Nitrogen monoxide
Hydrocarbons

Question 21

What are the three products of a catalytic converter?

Answer 21

Carbon dioxide
Nitrogen
Carbon dioxide and water

Question 22

What type of catalysis takes place in a catalytic converter?

Answer 22

Heterogeneous catalysis

Question 23

Why do catalytic converters have to be replaced sometimes?

2 reasons

Answer 23

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

Question 24

Comment on the life of a catalytic converted in a car where leaded petrol is used.

Answer 24

The catalytic converter will have a very short life as the lead will poison the catalysts

Question 25

Define a catalyst poison

Answer 25

A substance that makes a catalyst inactive

Question 26

What compound is more strongly adsorbed to the surface of the catalysts then any other compound in a leaded petrol vehicle?

Answer 26

Lead

Question 27

When changing a catalytic converter, does everything need to be replaced?

Answer 27

No as it is possible to recover most of the catalysts and recycle them