A heterogeneous catalyst is a substance that speeds up a chemical reaction without being consumed, and it exists in a different phase than the reactants. Typically, these catalysts are solid materials that facilitate reactions involving gases or liquids. Their surface provides active sites where reactants can adsorb, react, and then desorb as products. Common examples of heterogeneous catalysts include metals like platinum and palladium, which are often used in processes such as catalytic converters in vehicles. These catalysts are advantageous because they can be easily separated from the reaction mixture and reused, making them efficient for industrial applications.