Both the catalyst and the reactants are brought together in the same phase in homogeneous catalysis. Homogeneous catalysis refers to reactions that occur in the gas phase or, more commonly, the liquid phase; however, some reactions occur in the solid phase as well. Over the last two decades, homogeneous catalysis has grown in depth and reached to the point where tracing the borders of its current interest in organic synthesis, polymer and medicinal chemistry, for example, is challenging.
Catalysis is the acceleration of a chemical reaction by a chemical species that does not participate in the reaction's stoichiometry. Molecular catalysis is not a well-defined field, but it always refers to the application of molecular chemistry to chemical action, particularly molecular recognition and guest binding.