Biological catalysts are proteins known as enzymes.
Many industrial catalysts are metals. Iron, for example, is used to promote the reaction of nitrogen with hydrogen to synthesize ammonia. In automobiles, platinum-based catalytic converters convert engine exhaust to water and other benign byproducts. Designing catalytic systems to be fast acting and long-lived, and to form only the desired end products, has long been a major challenge. In many of these processes a stream of reactants, often at high temperature, is passed over tiny particles of metal on an oxide support surface.