Activity :
The ability of a catalyst in increasing the rate of reaction is defined as activity of catalyst.
`to` The activity of a catalyst depends upon the strength of chemisorption to a large extent .
`to` The reactions must get adsorbed reasonably strongly on to the catalyst to become reactive .
Eg : The catalystic activity increases from Group -5 to Group-11 for hydrogenation reactions.
The maximum activity being shown by 7-9 group metals.
`2H_(2_((g))) + O_(2_((g))) overset(Pt_((s)))to 2H_(2)O_((l))`
Selectivity :
The selectivity of a catalyst is its ability of direct a reaction to form specific products . The followign reactions indicate the selectivity of heterogeneous catalysis.
`to` Starting with `H_(2)` and CO, and using differnet catalysts, we get different products.
`CO_((g)) + 3H_(2_((g))) overset(Ni_((s)))to CH_(4_((g))) + H_(2)O_((g))`
`CO_((g))+2H_(2_((g))) underset(ZnO-Cr_(2)O_(3))overset(Cu_((s)))to CH_(3)OH_((g))`
`CO_((g))+H_(2_((g))) overset(Cu_((s))) to HCHO_((g))`
The action of a catalyst is highly selective in nature. A substance which acts as catalyst in one reaction any fail to catalyse another reaction.
