Which compound of transition metal is used as a catalyst in the Contact Process?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Vanadium (V) oxide
Transition metals and their compounds are good catalysts because they can change their oxidation state easily and form complexes with the reactants. In the Contact process for sulphuric acid, sulphur dioxide is oxidised to sulphur trioxide over vanadium(V) oxide:
\( \displaystyle \ce{2SO2 + O2} \xrightarrow{\ce{V2O5}} \ce{2SO3} \)
The vanadium shuttles between +5 and +4. \( \ce{V2O5} \) oxidises \( \ce{SO2} \), and oxygen then oxidises the reduced vanadium back:
\( \displaystyle \ce{SO2 + V2O5 -> SO3 + 2VO2} \)
\( \displaystyle \ce{4VO2 + O2 -> 2V2O5} \)
NCERT (2026-27 edition):
Catalytic Properties
