Why Does Platinum Metal Make a Good Catalytic Surface for Reactant Molecules??

This page looks at the the different types of catalyst (heterogeneous and homogeneous) with examples of each kind, and explanations of how they work. You will also find a description of one example of autocatalysis – a reaction which is catalysed by one of its products.

This is a solution reaction that you may well only meet in the context of catalysis, but it is a lovely example! Iodide ions are very easily oxidised to iodine.

And yet the reaction between them in solution in water is very slow. The reaction needs a collision between two negative ions. The catalysed reaction avoids that problem completely.

This is another good example of the use of transition metal compounds as catalysts because of their ability to change oxidation state. For the sake of argument, we’ll take the catalyst to be iron(II) ions. The iron(III) ions are strong enough oxidising agents to oxidise iodide ions to iodine.

In the process, they are reduced back to iron(II) ions again. Both of these individual stages in the overall reaction involve collision between positive and negative ions. This will be much more likely to be successful than collision between two negative ions in the uncatalysed reaction.

What happens if you use iron(III) ions as the catalyst instead of iron(II) ions? The reactions simply happen in a different order. This is a good example of homogeneous catalysis where everything is present as a gas.

Ozone, O 3 , is constantly being formed and broken up again in the high atmosphere by the action of ultraviolet light. Ordinary oxygen molecules absorb ultraviolet light and break into individual oxygen atoms. These have unpaired electrons, and are known as free radicals .

Ozone can also be split up again into ordinary oxygen and an oxygen radical by absorbing ultraviolet light. This formation and breaking up of ozone is going on all the time. Taken together, these reactions stop a lot of harmful ultraviolet radiation penetrating the atmosphere to reach the surface of the Earth.

The catalytic reaction we are interested in destroys the ozone and so stops it absorbing UV in this way. Chlorofluorocarbons (CFCs) like CF 2 Cl 2 , for example, were used extensively in aerosols and as refrigerants. Their slow breakdown in the atmosphere produces chlorine atoms – chlorine free radicals.

In the first, the ozone is broken up and a new free radical is produced. The chlorine radical catalyst is regenerated by a second reaction. This can happen in two ways depending on whether the ClO radical hits an ozone molecule or an oxygen radical.

If it hits an oxygen radical (produced from one of the reactions we’ve looked at previously):

Why platinum is a good catalyst?

Platinum works as a catalyst by collecting oxygen atoms (O), and letting them bind with the toxic carbon monoxide (CO), to create the less harmful carbon dioxide (CO2). … This provides for the first time a good explanation for the high catalytic activity of platinum in oxidation reactions.

What makes a good catalyst?

A good catalyst needs to adsorb the reactant molecules strongly enough for them to react, but not so strongly that the product molecules stick more or less permanently to the surface. Silver, for example, isn’t a good catalyst because it doesn’t form strong enough attachments with reactant molecules.

How do surface catalysts work?

The catalytic converter is also an example of surface catalysis, where the reactant molecules are adsorbed onto a solid surface before they react with the catalyst to form the product. The rate of a surface-catalyzed reaction increases with the surface area of catalyst in contact with the reactants.