Question

What do you understand by activity and selectivity of catalysts ?

Answer 1

(i) Activity of a catalyst The ability of a catalyst to join with the reactant molecules so that they start reacting faster is called activity increases from group 5 to 11. Among these maximum activity is shown by group 7 to 10 elements.

$2H_2+O_2\left(g\right)\stackrel{Pt}{\to }2H_{2}O\left(l\right)$

(ii) Selectivity of a catalyst The selectivity of a catalyst is its ability to direct a reaction to yield a particular product. e.g., reactants being same reacting with different catalysts (specific) produce different (specific) products.

(a) $CO\left(g\right)+3H_2\left(g\right)\stackrel{Ni}{\to }C{H}_4\left(g\right)+H_{2}O\left(g\right)$
(b) $CO\left(g\right)+2H_2\left(g\right)\stackrel{\frac{Cu}{ZnO-C{r}_2{O}_3}}{\to }C{H}_{3}OH\left(g\right)$
(c) $CO\left(g\right)+H_2\left(g\right)\stackrel{Cu}{\to }HCHO\left(g\right)$