Question

What is shape selective catalysis?

Answer 1

Hint: Catalysis is referred to the process of improving the rate of a reaction. As it can be explained from the name itself, shape selective catalysis depends upon the shape and size and other physical properties of the reactants. Shape selective catalysts are of different types, and are selected depending upon the size of the reactant.

Complete step by step answer:
As we know, catalysis is a process of increasing the rate (speed) of the reaction by using substance (catalyst) which does not change the reaction chemically neither get involved in the reaction.
-The catalytic reaction that depends upon the structure of the pores of the catalyst and the size of the molecules of the reactant and the product is known as shape-selective catalysis.
- Zeolites, a crystalline, aluminosilicate mineral, is a common shape selective catalyst and adsorbent. Zeolite is extremely porous and is resistant to factors like high temperature and pressure.
-Zeolite is used as a shape selective catalyst due to its uniform shape and size of the micropores. In a catalytic reaction, where zeolite is used, the molecules of the reactant are diffused in the pores of the mineral i.e. the molecule is trapped inside it and is later adsorbed in the active sites of the chemical reaction.
ZSM-5 which is a nanometer sized shape selective zeolite catalyst, is used as a highly effective isomerisation, polymerisation and a dehydration catalyst. It is used to convert methanol directly into gasoline (synthetic) along with a mixture of aromatic and aliphatic hydrocarbons on dehydrating.

Additional information:
There are many other zeolite catalysts which are used in the petrochemical industry and drug, fragrance industry.

Note: It is important to remember here that, shape selective catalysis depends upon the size of the pores of the catalyst as well as the size of the molecules of the reactant. If the size of the reactant molecule is greater than the pores of the catalyst, it won’t be diffused in the catalyst. Therefore, this has to be kept in mind while selecting a shape selective catalyst for a particular reaction.