Catalysis is a process of speeding up or enabling a chemical reaction using a substance that does not undergo permanent changes during the reaction. For a reaction to take place, chemical bonds must be broken and new ones formed. This requires energy and the amount needed is called the activation energy. A catalyst lowers this activation energy barrier, so the molecules can react more easily. The catalyst is not used up as part of the reaction, nor does it appear as a contaminant in the product.
There are different forms of catalysts, including homogeneous, heterogeneous and biocatalysts.