What is a catalyst?
A substance that increases the rate of a chemical reaction by lowering the energy of activation.
Some reactions require a catalyst. The catalyst is not consumed during the reaction, but needs to be present to allow the reaction to occur.
There are two main types of catalytic reactions, homogeneous (the substances are in two different phases e.g. solid, liquid) and heterogeneous (the substances are in the same phase).
For example the catalytic converter in a car changes poisonous molecules such as carbon monoxide into nonpoisonous molecules such as carbon dioxide. They use metals such as platinum or palladium as the heterogenous catalyst.
Enzymes are catalysts. They are proteins that accelerate the chemical reactions in our body.