A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It lowers the activation energy needed for the reaction to occur, allowing it to happen more quickly or at a lower temperature. Catalysts are essential in various industries, including pharmaceuticals and petrochemicals, where they help produce products efficiently. There are two main types of catalysts: homogeneous and heterogeneous. Homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase. Both types play crucial roles in making chemical processes more efficient and environmentally friendly.