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Summary ALEVEL CHEMISTRY - TRANSITION METAL CATALYSTS
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ALEVEL CHEMISTRY - TRANSITION METAL CATALYSTS
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Transition Metal CatalystsTransition Metals make good catalysts due to their variable oxidation states as they can gain or
lose electrons in the d-orbital.
This means they can transfer electrons to speed up reactions.
Contact Process
Vanadium oxide (V2O5) catalyses the industrial reaction to produce sulphuric acid in a two step
process called the contact process.
1. Vanadium (v) oxide oxidises SO2 to SO3 and itself is reduced to vanadium (iv) oxide.
2. The reduced catalyst is then itself reduced back to its original state by oxygen gas.
Heterogeneous Catalysts
A catalyst in a different phase from the reactants which are in a different physical state.
Examples include: Iron which is used in the Haber Process and Vanadium (v) Oxide which is
used in the Contact Process.
Adsorption
Reactants form bonds with atoms at the active site of the catalyst as the reactants
become adsorbed on the surface.
As a result bonds in the reactants are weakened and break.
New bonds form between reactants as they are held closely to the catalysts surface.
Bonds between products and the catalysts surface weaken as the product - deabsorbs
and leaves.
Some metals have too weak an adsorption (so do not adsorb in a high enough concentration)
while some are too strong so products are not released.
Most commonly Nickel and Platinum are good catalysts.
Surface Absorption Theory
1. Adsorption happens when one of the reactants attaches to the surface of the catalyst.
2. Reaction occurs on the catalysts surface as the bonds are broken and remade.
3. When the product is made it detaches from the surface and de-adsorption occurs.
Use of a Support Medium
When a heterogeneous catalyst is used the reaction happens on the surface of the catalyst.
This means increasing the surface area of the catalyst increases the number of molecules
which can react at the same time. Increases the rate of reaction.
A support medium is used to make the surface area of the catalyst as large as possible.
Catalytic Poisoning
Catalytic poisoning reduces the surface area of the catalyst available to the reactants. It
increases the costs of the chemical process. Impurities may bind to the catalysts surface
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