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Chemistry of the D-Block Transition Metals

Heterogeneous and homogeneous catalysis

  • 3 things to know
  • Component 1

Overview

Three stages of a reaction on a heterogeneous catalyst, how adsorption onto a surface speeds up a reaction and substance that poisons an industrial catalyst.

What you need to know

Answer each one before you reveal it.

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Key term

Why are most transition metal catalysts used in a different phase from the reactants?

Process

Outline the three stages of a reaction on a heterogeneous catalyst.

Process

Why is a poisoned transition metal catalyst so costly to an industrial process?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why are most transition metal catalysts used in a different phase from the reactants?

    Model answer

    The metal is a solid while the reactants are gases or in solution, so the reaction happens at the surface and the catalyst is easily recovered afterwards.

  2. 2

    Why can a transition metal ion in solution catalyse a reaction between two other ions?

    Model answer

    It can be oxidised by one of them and reduced back by the other, providing a two-step route of lower activation energy and emerging unchanged.

  3. 3

    Where does the reaction take place on a heterogeneous catalyst?

    Model answer

    On its surface, at positions called active sites.

  4. 4

    Outline the three stages of a reaction on a heterogeneous catalyst.

    Model answer

    The reactant molecules are adsorbed onto the surface, they react there, and the products are then desorbed.

  5. 5

    Explain how adsorption onto a surface speeds up a reaction.

    Model answer

    It holds the reactants close together in a favourable orientation and weakens their bonds, which lowers the activation energy.

  6. 6

    Why is a heterogeneous catalyst usually used as a fine powder or as a thin coating on a support?

    Model answer

    This gives the greatest surface area per unit mass, so more active sites are available and less of the costly metal is needed.

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