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Alkanes

Catalytic converters

  • 3 things to know
  • Unit AS 2

Overview

Purpose of a catalytic converter in a car exhaust, catalysis takes place in a catalytic converter and catalyst poisoning.

What you need to know

Answer each one before you reveal it.

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Key term

Outline how a heterogeneous catalyst brings about a reaction between two gases.

Key term

What is the purpose of a catalytic converter in a car exhaust?

Key term

Which metals are used as the catalyst in a catalytic converter?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the purpose of a catalytic converter in a car exhaust?

    Model answer

    It converts the harmful gases leaving the engine, namely carbon monoxide, oxides of nitrogen and unburned hydrocarbons, into less harmful carbon dioxide, nitrogen and water before they reach the air.

  2. 2

    Which metals are used as the catalyst in a catalytic converter?

    Model answer

    Platinum, palladium and rhodium are used as the catalyst.

  3. 3

    Why is the catalyst spread as a very thin coating over a ceramic honeycomb?

    Model answer

    The honeycomb gives an extremely large surface area on which the reactions can happen while using only a small mass of very expensive metal.

  4. 4

    What type of catalysis takes place in a catalytic converter?

    Model answer

    It is heterogeneous catalysis, because the catalyst is a solid while the reacting exhaust gases are in the gas phase.

  5. 5

    Outline how a heterogeneous catalyst brings about a reaction between two gases.

    Model answer

    The gas molecules are adsorbed onto the metal surface, which weakens their bonds and holds them close together in a favourable orientation, they then react, and the products are finally desorbed to free the surface.

  6. 6

    Write the equation for the reaction between carbon monoxide and nitrogen monoxide in a catalytic converter.

    Model answer

    The equation is 2CO(g) + 2NO(g) → 2CO₂(g) + N₂(g).

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