Which of the following does not involve Pt as catalyst?
(A) contact process for making \( H_2SO_4 \).
(B) Ziegler-Natta catalyst.
(C) Adams catalyst, used for reduction.
(D) catalyst to decompose \( KClO_3 \) to give \( O_2 \).
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B) and (D) only
Each industrial or laboratory process uses a catalyst chosen for its activity, cost and resistance to poisoning. Platinum is a powerful hydrogenation and oxidation catalyst, but it is expensive and easily poisoned, so cheaper catalysts have replaced it in most large-scale processes.
(A) contact process for making \( \ce{H2SO4} \) — Does not involve Pt. Platinum was used at first, but it is costly and poisoned by impurities; the oxidation of \( \ce{SO2} \) now uses vanadium(V) oxide:
\( \displaystyle \ce{2SO2 + O2} \xrightarrow{\ce{V2O5}} \ce{2SO3} \)
(B) Ziegler-Natta catalyst — Does not involve Pt. It is a mixture of titanium tetrachloride and triethylaluminium, \( \ce{TiCl4 + Al(C2H5)3} \), used to polymerise ethene and propene.
(C) Adams catalyst, used for reduction — Involves Pt. Adams catalyst is platinum dioxide, \( \ce{PtO2} \), which is reduced by hydrogen to finely divided platinum and used to hydrogenate alkenes and other groups.
(D) catalyst to decompose \( \ce{KClO3} \) to give \( \ce{O2} \) — Does not involve Pt. Manganese dioxide is the catalyst:
\( \displaystyle \ce{2KClO3} \xrightarrow[\Delta]{\ce{MnO2}} \ce{2KCl + 3O2} \)
NCERT (2026-27 edition):
Some Applications of d- and f-Block Elements – “… Many of the metals and/or their compounds are essential catalysts in the chemical industry. V2O5 catalyses the oxidation of SO2 in the manufacture of sulphuric acid. TiCl4 with Al(CH3)3 forms the basis of the Ziegler catalysts used to manufacture polyethylene (polythene). Iron catalysts are used in the Haber process for the production of ammonia from N2/H2 mixtures.”