Question

What do you understand by shape-selective catalysis? Why are zeolites good shape-selective catalysts?

Answer 1

Hint : Catalysis is the process of changing the rate of a chemical reaction by adding a catalyst. Catalysts are not consumed during the catalyzed reaction, so they remain unchanged afterward. Often, only a trace amount of catalyst is required.

Complete Step By Step Answer:
Shape-selective catalysis refers to a catalytic reaction that is dependent on the molecules of the product, the size of the reactant, and the pore structure of the catalyst. As an example: The catalysis reaction using zeolite is an example of shape-selective catalysis. As a result, molecules with pore sizes larger than 260-740 pm are unable to pass through the zeolite and experience the reaction.
Zeolites are crystalline solid structures composed of silicon, aluminum, and oxygen that form a framework with cavities and channels inside that can house cations, water, and/or small molecules. They are also commonly referred to as molecular sieves.
Because of their honeycomb-like structures, zeolites are excellent shape-selective catalysts. They are aluminosilicates with a three-dimensional silicate network in which some silicon atoms are replaced by aluminum atoms, resulting in an Al-O-Si framework.
The reactions that occur in zeolites are determined by the size and shape of the reactant and product molecules, as well as the pores and cavities of the zeolites. They can be found in nature as well as synthesized to improve the selectivity of catalysts. Zeolites are widely used as catalysts in the petrochemical industry for hydrocarbon cracking and isomerization.

Note :
Selective Catalytic Reduction (SCR) is an advanced active emissions control technology system that injects a liquid-reducing agent into the exhaust stream of a diesel engine via a special catalyst. Typically, the reductant source is automotive-grade urea, also known as Diesel Exhaust Fluid (DEF).