Homogeneous catalysis

In chemistry, homogeneous catalysis is catalysis in a solution by a soluble catalyst. Homogeneous catalysis refers to catalytic reactions where the catalyst is in the same phase as the reactants. Homogeneous catalysis applies to reactions in the gas phase and even in solids. 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 often implies catalysis by organometallic compounds. In chemistry, homogeneous catalysis is catalysis in a solution by a soluble catalyst. Homogeneous catalysis refers to catalytic reactions where the catalyst is in the same phase as the reactants. Homogeneous catalysis applies to reactions in the gas phase and even in solids. 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 often implies catalysis by organometallic compounds. Homogeneous catalysis using transition metal complexes is an area of research that has grown enormously in recent years. Many remarkable catalytic discoveries have been reported by researchers both in industry and in academia. The area is one of intense research and many practical applications, e.g., the production of acetic acid. Enzymes are examples of homogeneous catalysts. When materials react to form products, there may be a single reaction or multiple reactions occurring. A single reaction can be called an elementary. For most reactions, the sequence of elementary steps that constitute their mechanism is not known. Sometimes only a single reaction is observed. The reason is that the amount of the intermediate species formed is very small and escapes detection. The speed with which these intermediate species are created and destroyed also makes them difficult to detect. The general scheme is 'reactants --> several intermediate species --> products'.In the case of a non-elementary reaction, the test of the validity of the mechanism proposed is whether the predicted kinetics corresponds to experimental observation. Sometimes reactions may proceed by more than one mechanism, or else their kinetics can be explained by several mechanisms. There are zero-order, first-order, second-order, and higher-order processes. • Homogeneous catalysts are effective at being highly selective towards producing the desired product.• If a reaction is exothermic, it will release a lot of heat. It is easier to release heat from a solution (as one would do for a homogeneous catalyst) than if one were to use a heterogeneous catalyst, which tends to be an insoluble solid in the solution that adsorbs reaction participants onto it.• Reactants can easily access the homogeneous catalyst because it is in solution already! This promotes high catalytic activity.• Species in solution are easier to characterize (e.g. with various spectroscopy techniques) than species adsorbed onto a solid surface. • A catalyst capable of dissolving in solution will need to be separated later if it is to be recycled for re-usage (as per the principles of green chemistry).• The homogeneous catalyst may have issues at high temperatures since it is not desirable for the solution (which contains the catalyst) and any volatile reactants to evaporate, even though high temperatures usually promote faster reactions. The proton is the most pervasive homogeneous catalyst because water is the most common solvent. Water forms protons by the process of self-ionization of water. In an illustrative case, acids accelerate (catalyze) the hydrolysis of esters: