catalyst

Substance that alters the speed of, or makes possible, a chemical or biochemical reaction but remains unchanged at the end of the reaction. Enzymes are natural biochemical catalysts. In practice most catalysts are used to speed up reactions.

The catalysts used in the chemical industry are often transition metals or their compounds. According to the collision theory, particles must collide before they can react, and the colliding particles must contain enough energy to cause bonds to break. Catalysts increase the rate of reaction by lowering the amount of energy needed for a successful collision. Therefore, more collisions will be successful.