Catalysts are materials that speed up a chemical reaction, in a refinery or a fertiliser plant, without being used up themselves. Many reactions that industry needs are so slow, at normal heat and pressure, that making them useful would take far too long. A catalyst gives the reaction an easier path. The reaction runs fast, and the catalyst can be used again.
A catalyst is usually a solid, such as small pellets packed in a tall steel vessel called a reactor. The gas or liquid passes through the pellets, and the reaction happens on their surface. That is why catalysts are made with a very large surface, full of tiny holes. A spoonful of pellets can have the surface area of a room. Over the years the pellets get dirty or worn, and the plant replaces them. A plant planning a shutdown for replacement counts the lost production in crores of rupees, so makers sell catalysts on how long they last.
Consider the catalytic converter under a petrol car. It is a honeycomb of ceramic coated with a thin layer of platinum, palladium and rhodium. Hot exhaust gas passes through the honeycomb. On the metal surface, poisonous carbon monoxide turns into carbon dioxide, and unburnt fuel turns into carbon dioxide and water. The metals are not used up, so the converter lasts for years. Without it, a car cannot meet India's emission norms. The diagram of this page shows a different case, the iron catalyst of a fertiliser plant.
Catalysts are a kind of speciality chemicals. They are made for exactly one reaction and are sold to refineries and fertiliser plants, which rarely change them. Many of the leading makers are foreign, and Indian plants import most of their catalysts. Catalysts are also used in making green hydrogen, which is produced by an electrolyser. The search for a better catalyst is one of the first uses of AI materials discovery. The area is described in materials science.