SCIENCE

There are two types of catalysts: heterogeneous catalysts and homogeneous catalysts.

Heterogeneous catalysts are those that exist in different phases from the reactants, such as when a solid catalyst is used in a gas or liquid reaction. Examples of heterogeneous catalysts include activated charcoal, noble metals such as platinum, palladium and rhodium, and Lewis acid catalysts such as aluminum chloride or sulfates.

Homogeneous catalysts are those that exist in the same phase as the reactants. Examples of homogeneous catalysts include enzymes, acids, bases, and transition metal complexes.