In chemistry, homogeneous catalysis is catalysis in a solution by a soluble catalyst. Strictly speaking, homogeneous catalysis are catalytic reactions where the catalyst is in the same phase as the reactants, so homogeneous catalysis applies to reactions in the gas phase and even in a solid.  Heterogeneous catalysis is the alternative to homogeneous catalysis, where the catalysis occurs at the interface of two phases, typically gas-solid. The term is used almost exclusively to describe solutions and it is often implies catalysis by organometallic compounds. The area is one of intense research and many practical apprehended applications, e.g., the production of acetic acid. Enzymes are examples of homogeneous catalysts.