What Is a Homogeneous Catalyst?

The catalyst and the reactant are in the same phase without any phase boundary. The reaction is called homogeneous catalysis, and the catalyst capable of homogeneous catalysis is a homogeneous catalyst. Homogeneous catalysts include liquid acids, base catalysts, and Secoys solid acid hydrazones and basic catalysts, soluble transition metal compounds (salts and complexes), and the like. Homogeneous catalysts act independently as molecules or ions, with uniform active centers, high activity and high selectivity. ^[1]

Industrial applications of homogeneous catalysts are later than heterogeneous catalysts. For example, in 1959, platinum catalysts were used to oxidize ethylene to acetaldehyde, and later they were widely used in petrochemicals, such as the oxidation of propylene to acetone, the oxidation of butene to methyl ethyl alcohol, the oxidation of ethylene and acetic acid to vinyl acetate, and the conversion of ethylene to propylene, ethylene and Chlorine to vinyl chloride and so on. In addition to palladium chloride, palladium acetate, palladium nitrate, and organic palladium complexes can be used as homogeneous catalysts.

At the end of the 1960s, there was another

Homogeneous catalysis refers to a catalytic reaction system in which the catalyst is indistinguishable from the reaction medium and forms a homogeneous phase with other components in the medium. Homogeneous catalysis is often used in liquid phase reactions. In the material that undergoes the catalytic reaction, whether it is the reaction raw material or the catalyst, they are dissolved in the reaction medium and dispersed in an independent molecular form. ^[3]

In a homogeneous catalysis reaction using a transition metal complex as the active center, the catalytically active intermediate complex can separate crystals. Using x-ray analysis, the environment around the active center and the action status of the reaction poplar can be detailed Understand and use to make a more accurate depiction of the reaction mechanism. Through a thorough study of the partial reaction mechanism, can it be concluded that the elementary reaction steps of homogeneous complex catalysis are all performed on a metal-centered sphere, and the reaction process constitutes a catalytic cycle. The performance of the catalyst is easy Modifications and improvements are achieved through modulation of the ligand. Therefore, compared with heterogeneous catalysis, homogeneous catalysis has some own advantages: single reaction performance and specific selectivity; mild reaction conditions are conducive to energy saving; because its mechanism of action is relatively clear and clear, it is easy to design and deploy research and grasp. Therefore, the catalytic science community generally agrees that the research results of homogeneous catalysis systems took 5 years, and the research results of more phase catalysis systems are more abundant. The main disadvantages of homogeneous catalysis are poor stability and difficulty in separating products. One of the main research and development directions is to immobilize homogeneous catalysts. The carriers used for immobilization include organic polymers such as PS, PVC, and ion exchange resins, Al ₂ O ₃ , SiO ₂ , TiO ₂ , and molecular sieves Inorganic polymers. The method of immobilization is to anchor the active component metal atoms to these ionomers. ^[3]

1.Methanol carbonylation to acetic acid

This synthetic reaction was promoted to industrialization in the 1970s. It is another great achievement of homogeneous complex catalysis, which reflects the development of homogeneous catalysis. The significance of this complex catalysis reaction is the non-petroleumization of the raw material route. The successful development of the process coincided with the first global oil crisis, soaring crude oil prices, and shortage of petroleum resources, prompting people to realize that energy and organic synthetic raw materials should not rely too much on petroleum and should be diversified. ^[3]

2.Direct oxidation of ethylene to acetaldehyde

This is the Wacker process invented in the 1960s and is one of the most prominent achievements in the chemical industry. The significance is that the transition metal-ethylene chemistry was the first to achieve an industrially catalyzed oxidation reaction. Ethylene chemistry replaced the previous acetylene chemistry and promoted the rise and development of petrochemicals; secondly, for the first time, it indicated that noble metals can be economically used in domestic industrial production in homogeneous catalytic reactions, and promoted the study of transition metal complexation . ^[3]