A discussion on Catalysis.

2SO2(g) + O2(g) › 2SO3(g)

NO2(g)

A catalyst that is in a separate phase from the reactants is said to be a heterogeneous, or contact, catalyst. Contact catalysts are materials with the capability of adsorbing molecules of gases or liquids onto their surfaces. An example of heterogeneous catalysis is the use of finely divided platinum to catalyse the reaction of carbon monoxide with oxygen to form carbon dioxide. This reaction is used in catalytic converters mounted in automobiles to eliminate carbon monoxide from the exhaust gases.

Some substances, called promoters, do not have catalytic ability by themselves but increase the effectiveness of a catalyst. For example, if aluminium is added to finely divided iron, it increases the ability of the iron to catalyse the formation of ammonia from a mixture of nitrogen and hydrogen. Materials that reduce the effectiveness of a catalyst, on the other hand, are referred to as poisons. Lead compounds reduce the ability of platinum to act as a catalyst; therefore, an automobile equipped with a catalytic converter for emission control must be fuelled with unleaded gasoline.

Jas Harrar L6W

23/04/07