catalyst science definition
A catalyst is a substance that will change the rate of a reaction. A catalyst is often used to make a reaction go faster. The catalyst does not take part in the reaction as a reactant. It is not changed by the reaction or used up during the reaction. It is still there in the same form when the reaction is complete. A catalyst can be a transition metal, a transition metal oxide (see the uses of transition metals) or an enzyme. An exception is aluminium oxide, used for the cracking of hydrocarbons. A substance which works well as a catalyst for one reaction might not work well as a catalyst for a different reaction.