BharatNotes What is Catalysis?
Catalysis is the phenomenon of altering the rate of a chemical reaction by introducing a substance — a catalyst — that participates in the reaction but is not permanently consumed by it. A catalyst works by offering an alternative reaction pathway with a lower activation energy, so that a larger fraction of colliding molecules have enough energy to react (as described by the Arrhenius equation). Crucially, a catalyst does not change the position of equilibrium or the enthalpy of the reaction — it only helps the system reach equilibrium faster. A substance that slows a reaction is called an inhibitor or negative catalyst.
Types of Catalysis
| Type | Phase relationship | Typical example |
|---|---|---|
| Homogeneous | Catalyst in same phase as reactants (usually solution) | Hydroformylation (oxo process) using soluble Rh/Co complexes |
| Heterogeneous | Catalyst in a different phase (solid) from reactants (gas/liquid) | Iron in the Haber process; Pt/Pd/Rh in catalytic converters |
| Biocatalysis (enzymes) | Protein catalysts in living systems | Digestive enzymes; nitrogenase fixing nitrogen |
Heterogeneous catalysts act at their surfaces, where reactants adsorb, react and then desorb — which is why surface area and metal choice matter enormously. Enzymes are prized for extraordinary specificity and efficiency under mild temperature and pH.
Industrial and Environmental Significance
Catalysis enables a large share of the global chemical economy. The Haber-Bosch process synthesises ammonia (for fertilisers) from nitrogen and hydrogen over a promoted iron catalyst, typically at roughly 400-500°C and 150-300 atmospheres; the catalyst makes the otherwise sluggish reaction industrially viable.
In emission control, the three-way catalytic converter uses platinum, palladium and rhodium to simultaneously: reduce nitrogen oxides (NOx) to N2; oxidise carbon monoxide (CO) to CO2; and oxidise unburnt hydrocarbons to CO2 and water. Rhodium chiefly drives NOx reduction, while platinum and palladium handle oxidation.
Catalysis is one of the 12 Principles of Green Chemistry (US EPA framework): because catalytic reagents work in small amounts and act repeatedly, they cut waste and energy use far more than stoichiometric reagents.
Current Status and India Angle
India's Bharat Stage VI (BS-VI) vehicular norms — rolled out nationwide from 1 April 2020 — tightened pollutant limits sharply versus BS-IV (NOx lowered roughly 70% for diesel and 25% for petrol, per industry reporting). Meeting them required advanced after-treatment such as Diesel Oxidation Catalysts (DOC), Selective Catalytic Reduction (SCR) and Diesel Particulate Filters (DPF), alongside ultra-low-sulphur fuel — all catalysis-dependent technologies. Bharat Stage norms are notified under the Ministry of Environment, Forest and Climate Change framework.
UPSC Angle
For Prelims, remember the non-negotiable facts: a catalyst lowers activation energy and speeds the reaction but does not shift equilibrium or change the energetics, and it is recovered unchanged. Know the Pt-Pd-Rh trio in catalytic converters and the iron catalyst in the Haber process. For GS3, link catalysis to green chemistry, fertiliser self-sufficiency and vehicular-pollution control under BS-VI. Foundation concept — no direct PYQ; underpins recurring questions on chemical kinetics, fertilisers and air-pollution mitigation.
