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Catalysis, importance, intermediate compound theory

Short answer

Catalysis is the change of reaction rate by a substance not consumed, vital for industrial processes like ammonia and sulfuric acid manufacture, enabling lower energy use. The intermediate theory explains it through unstable compounds regenerating the catalyst, exemplified by NO in the lead chamber process and V₂O₅ in the contact process.

What is meant by catalysis? Point out its importance. Discuss intermediate compound formation theory of catalysis with suitable examples.

Catalysis

A catalyst is a substance that changes the rate of a chemical reaction without being consumed in the reaction (its mass and chemical nature are the same at the end). The phenomenon is called catalysis. Example: MnO₂ speeds up the decomposition of KClO₃ to O₂.

Importance of catalysis

  • Manufacture of ammonia (Fe, Haber), H₂SO₄ (V₂O₅, contact), HNO₃ (Pt, Ostwald) and methanol.
  • Hydrogenation of vegetable oils to ghee (Ni).
  • Petroleum cracking and reforming (zeolites, Pt).
  • Control of vehicle pollution: catalytic converters with Pt/Pd/Rh.
  • Biological systems: enzymes catalyse digestion and metabolism.
  • Catalysts allow lower temperature and pressure, saving fuel and cost, and give better yields.

Intermediate compound formation theory

According to the intermediate compound formation theory, the catalyst takes part in the reaction by forming an unstable intermediate compound with one of the reactants. The intermediate has a lower activation energy path and reacts with the other reactant to give the product and regenerate the catalyst.

Uncatalysed:  A + B  ───────────→  AB        (high Ea)
Catalysed  :  A + C  →  [AC]       (fast, low Ea)
              [AC] + B → AB + C    (fast, low Ea)
              (C = catalyst, regenerated)

Examples

  1. Lead chamber process (NO as catalyst): 2NO + O₂ → 2NO₂ (intermediate) NO₂ + SO₂ → SO₃ + NO (catalyst regenerated)
  2. Preparation of diethyl ether from ethanol with conc. H₂SO₄: C₂H₅OH + H₂SO₄ → C₂H₅HSO₄ (ethyl hydrogen sulphate) + H₂O C₂H₅HSO₄ + C₂H₅OH → C₂H₅OC₂H₅ + H₂SO₄
  3. Contact process with V₂O₅: V₂O₅ + SO₂ → V₂O₄ + SO₃, then V₂O₄ + ½O₂ → V₂O₅.

Limitation: it explains homogeneous catalysis well, but is not suitable for many heterogeneous cases where no stable intermediate is found.

✓ Answer checked by Claude Opus 5.5 (high effort)

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