Catalyst Life Expectancy
Although catalysts take part
in the reaction, they are not reactants and do not feature in
the chemical equation. In practice, however, catalysts may be
destroyed during product extraction, may be vaporised during use,
and may require recovery.
Nitric acid is produced by the oxidation of ammonia using a platinum/rhodium
metal catalyst. During operation platinum is oxidised and vaporised,
and must be recovered to prevent its inclusion in the product.
The development of more sophisticated catalytic gauzes, and oxidation
at lower pressure, has resulted in reduced loss of catalyst. More
details can be found in the nitric
The aim is always to find a
catalyst that can be reused many times, though this may depend
on how the catalyst is used, not just on which catalyst is used.
The Turnover Number (TON) is a measure of how long a catalyst
can be used before it needs replacing. A TON in excess of 1 million
indicates a stable, long-lived catalyst.
a detailed discussion of catalysis, see the catalysis-ed