What Is a Catalyst?

Catalysts work by providing an alternative reaction pathway with a lower activation energy barrier. They participate in intermediate steps but are regenerated by the end of the reaction cycle. Catalysts can be homogeneous (in the same phase as reactants, like dissolved acid catalysts) or heterogeneous (in a different phase, like solid platinum in a car catalytic converter). Enzymes are biological catalysts — proteins that accelerate biochemical reactions by factors of millions to billions; without enzymes, essential metabolic reactions would take years. The Haber-Bosch process uses an iron catalyst to synthesise ammonia from nitrogen and hydrogen at industrial scale, producing fertiliser that feeds roughly half the world population. Catalytic converters in cars use platinum, palladium, and rhodium to convert toxic exhaust gases (CO, NOx, hydrocarbons) into less harmful CO2, N2, and water.