Question

Which one of the following statements is not correct about zeolites?

• A. These are water softners
• B. These do not act as molecular sieves
• C. They are complex oxide catalysts commonly used in petrochemical industries
• D. The activity of zeolites is increased by heating them in vacuum

Answer 1

Answer: (B)

These do not act as molecular sieves

The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules is called shape-selective catalysis. Zeolites are good shape-selective catalysts because of their honeycomb-like structures. An important zeolite catalyst used in the petroleum industry is ZSM-$5$. It converts alcohol directly into gasoline (petrol).

This is because of the following:

(A) Zeolites are natural ion exchangers. They take up calcium ions from hard water and release sodium ions in water. Hence, they act as water softeners. Hence, option A is correct.

(B) Zeolites trap small molecules (such as water, ammonia and carbon dioxide) in their interstices reversibly. Hence, they act as molecular sieves. Thus, option B is not correct.

(C) Zeolites are complex oxide catalysts commonly used in petrochemical industries. Hence, option C is correct.

(D) The activity of zeolites is increased by heating them in a vacuum. Hence, option D is correct.