What is desired in a catalyst is
Different kinds of substances are effective in different kinds of reactions. Examples are:
Fe, Ni, Pt, Ag, Ru
|insulating||dehydration||Al2O3, SiO2, MgO|
H3PO4, H2SO4, SiO2/ Al2O3, zeolites
Catalyst activity for metals is highest towards the middle of the d-block.
Turnover factor is the number of molecules converted by each catalytic site in a unit of time. The most active enzymes have a turnover factor of 1010/hr. This activity is matched by the acid sites in some model zeolite catalysts. Typical industrial catalysts have turnover factors of between 103 and 105/hr.
A selectivity of 99.99% means that the catalyst makes one mistake in 10,000
conversions. This is the performance achieved by enzymes in living systems,
though most enzymes do better than this.
Few synthetic industrial catalysts achieve this degree of control over the chemistry they catalyse.
The number of reactions performed by each active site before it decays or becomes inactive, or the catalyst has to be disposed of is of great importance. Fine chemical manufacture demands in excess of 1,000,000 reactions per active site.