Catalyst used in hydrogenation of vegetable oil into vanaspati ghee is

Question

UnlockIAS · Accepted Answer

Correct — A, Ni. Vanaspati is made by hardening liquid vegetable oil, and the chemistry behind it is one reaction. Vegetable oils are triglycerides of unsaturated fatty acids: their hydrocarbon chains carry carbon–carbon double bonds, and each double bond puts a kink in the chain that keeps the molecules from packing closely, which is why the oil is liquid at room temperature. Pass hydrogen gas through the hot oil over a catalyst and hydrogen adds across those double bonds, straightening the chains, raising the melting point and turning the oil into a semi-solid fat. The catalyst that makes this happen at industrial scale is finely divided NICKEL, used at roughly 450 to 500 kelvin under a few atmospheres of hydrogen — the process patented by Wilhelm Normann in 1903 and the reason vanaspati exists at all. Nickel wins on economics as much as chemistry: it is an effective hydrogenation catalyst, it can be prepared with an enormous surface area by reducing nickel oxide or by leaching aluminium out of a nickel-aluminium alloy to give Raney nickel, and it is cheap enough to use by the tonne in an edible-oil plant. Note also what the catalyst does not do: it does not appear in the product and is filtered out after the reaction, since a catalyst changes the rate of a reaction by offering a lower-energy path and is recovered unchanged. Because option (a) is right, the escape option (d) cannot stand. One consequence worth knowing is that partial hydrogenation converts some of the remaining cis double bonds into the trans form, and trans fats raise LDL cholesterol while lowering HDL — which is why India's food regulator has progressively capped trans fatty acids in edible oils and fats.

Why the other options are wrong — (b) Chemically right and economically impossible, which makes it the thinking candidate's mistake. Palladium — usually as palladium on carbon — is an excellent hydrogenation catalyst and is the standard choice in a laboratory or in fine-chemical synthesis, along with platinum. It is a precious metal costing many times what nickel does, and no edible-oil refinery hardening thousands of tonnes a year would use it.  (c) Iron is a famous industrial catalyst, but for a different reaction entirely: finely divided iron with promoters such as potassium and aluminium oxide is the catalyst of the Haber process, which combines nitrogen and hydrogen to make ammonia. Seeing 'catalyst' and 'hydrogen' in the same stem and reaching for iron is exactly the association the option is built on.  (d) Fails because nickel is squarely on the list. An escape option is correct only when each of the other three can be shown to be wrong, and here the first of them is the catalyst named in every school and undergraduate account of oil hardening.

Concept: A catalyst speeds a reaction by providing a path with a lower activation energy, and emerges chemically unchanged at the end. Heterogeneous catalysts, like the nickel used here, are in a different phase from the reactants — a solid in contact with a liquid and a gas — and they work at their surface: hydrogen molecules adsorb onto the metal and are split into atoms, the double bond of the fatty acid chain adsorbs alongside, the hydrogen atoms add across it, and the saturated chain desorbs. Everything about the catalyst's design therefore aims at surface area, which is why it is used finely divided. The wider family is worth holding as a table: nickel for the hydrogenation of oils, iron for ammonia in the Haber process, vanadium pentoxide for sulphur trioxide in the Contact process, platinum-rhodium gauze for nitric oxide in the Ostwald process, and Ziegler-Natta catalysts for polymerisation.

State PCS 2025 Q26 — Science & Technology PYQ with Answer

State PCS 2025 Q26 — Science & Technology PYQ with Answer