Adsorption and Colloids — Chemistry STD 11 Science — Question
Maharashtra BoardEnglish MediumSTD 11 ScienceChemistryAdsorption and Colloids6 Marks
Question
Describe heterogeneous catalysis with the help of one example.
✓
Answer
$i.$ When the reactants and catalyst are in different phase, it is said to be heterogeneous catalysis.
$ii.$ The heterogeneous catalyst is generally a solid and the reactants may either be gases or liquids.
$iii.$ When the solid catalyst is added to the reaction mixture, it does not dissolve in the reacting system and the reaction occurs on the surface of the solid catalyst.
e.g. Dinitrogen $(N_2)$ and dihydrogen $(H_2)$ combine to form ammonia in Haber process in the presence of finely divided iron along with $K_2O$ and $Al_2O_3.$
$\underset{\text { Nitrogen }}{ N _{2( g )}}+\underset{\text { Hydrogen }}{3 H _{2( g )}} \xrightarrow[ K _2 O , Al _2 O _3]{ F _{( s )}} \underset{\text { Ammonia }}{2 NH _{3( g )}}$
$b.$ In the above reaction, $Al_2O_3$ and $K_2O$ are promoters of the $Fe$ catalyst. $Al_2O_3$ is added to prevent the fusion of $Fe$ particles. $K_2O$ causes chemisorption of nitrogen atoms. Molybdenum is also used as promoter.
$c.$ Since the reactants are present in gaseous phase while the catalyst used is in solid phase, it represents heterogeneous catalysis.
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