A catalyst is a substance that accelerates a reaction but is not part of the reaction products. The amount of catalyst unlike other reagents, after the reaction does not change. Providing a faster path for reaction, the catalyst reacts with the original substance, the resulting intermediate compound is subjected to transformations and in the end splits into the product and catalyst. Then the catalyst again reacts with the starting material, and this catalytic cycle repeatedly (up to a million times) is repeated.
Catalysts are substances that changes the rate of chemical reaktsii or causing it, but not included in the products.