Pollutants from combustion

Pollutants from combustion

Answer these questions

1) Name an alkane with between 4 and 8 carbon atoms2) Write a balanced symbol equation for the complete

combustion of this alkane3) What happens if there is a limited supply of oxygen?

4) How can we reduce the amount of atmospheric pollutants from combustion?

Aims

- Understand how air pollutants can be formed in a combustion engine

- Understand how a catalytic converter works

HydrocarbonsOxygen

Nitrogen

The internal combustion engine

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HydrocarbonsOxygen

Nitrogen

The internal combustion engine

Carbon monoxide

Nitrogen oxides (NOx)

Unburnt hydrocarbons

Carbon monoxide

- Poisonous gas produced from incomplete combustion

- Comes mainly from traffic pollution

- Exists for about 1 month before being oxidised to CO2

- Toxic to humans: bind strongly with haemoglobin and prevents oxygen being supplied to tissues

Nitrogen oxides (NOx)

Air is drawn into combustion engine with fuel

The high temperatures produced mean that nitrogen from air can react with oxygen

NO2 is linked to formation of low level ozone

Converted to nitric acid: contributor towards acid rain

Respiratory irritants

Unburnt hydrocarbons

- Released in exhaust gases

- Benzene and buta-1,3-diene are released in small quantities: human carcinogens

- React with NOx to form low-level ozone (energy from UV light allows this to happen) and photochemical smog.

- Low level ozone causes breathing difficulties & susceptibility to infections.

Infra-red spectroscopy can be used to monitor environmental pollution

Removing pollutants from vehicle exhaust

The catalyst coating is normally an expensive metal:• platinum (Pt)• rhodium (Rh)• palladium (Pd)

They can’t remove particulates (carbon particles). These are removed via a separate particulate trap or a diesel particulate filter.

The catalytic converter

In the catalytic converter

1) Adsorption of CO and NO to the catalyst surface2) Temporary bonds form between the catalyst and gas

molecules. Chemical reaction takes place3) Desorption of CO2 and N2 from the catalyst surface

Important equations for reactions in catalytic converters: Oxidation catalysts

1. Oxidation of carbon monoxide to carbon dioxide:

2CO + O2 2CO2

2. Oxidation of unburnt hydrocarbons (HCs) to carbon dioxide and water:

C12H26 + 18.5 O2 12CO2 + 13H2O

In a three way catalyst NO reacts with CO

1. Reduction of nitrogen oxides to nitrogen and oxygen:

2NOx xO2 + N2

Catalysts

A catalyst speeds up a reaction without being consumed by the overall reaction.

Catalysts

• Catalysts reduce the activation energy needed for a reaction

• They do this by offering an alternate route for the reaction to take (for example via an intermediate)

• Lower activation energy means more successful collisions

• More successful collisions means faster rate

Catalysts are very useful in industry

- They often require lower temperatures than uncatalysed reactions, which reduces the energy demand and carbon dioxide emissions from fossil fuels.

- They allow different reactions to be used with a better atom economy and reduced waste.

- They are often enzymes which allow processes to operate at lower temperatures and pressures

Examples of economically important catalysts

Iron in ammonia production

Ziegler– Natta catalyst in poly(ethene) production

Platinum/palladium/rhodium in catalytic converters

Catalysts and the Boltzmann distribution

Make notes on carbon capture and storage on page 224-225

Make notes on uses for CO2 on page 234-235

Complete question 11 on page 237

Prep: Exam questions