There are many types of catalysts, which can be divided into liquid catalysts and solid catalysts according to their states; according to the phase state of the reaction system, they are divided into homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts include acid, alkali, soluble transition metal compound and peroxide catalyst. Heterogeneous catalysts include solid acid catalysts, organic base catalysts, metal catalysts, metal oxide catalysts, complex catalysts, rare earth catalysts, molecular sieve catalysts, biological catalysts, nano catalysts, etc.; according to the type of reaction, they are divided into polymerization, polycondensation, and esterification. , Acetalization, hydrogenation, dehydrogenation, oxidation, reduction, alkylation, isomerization and other catalysts; according to the size of the role is also divided into main catalyst and promoter.
Homogeneous catalysis
The catalyst and the reactants are in the same phase without the existence of a phase boundary. The reaction is called homogeneous catalysis. The catalyst that can play a homogeneous catalysis is a homogeneous catalyst. Homogeneous catalysts include liquid acids, base catalysts, solid acid and alkaline catalysts, and soluble transition metal compounds (salts and complexes). Homogeneous catalysts act independently of molecules or ions, with uniform active centers, high activity and high selectivity.
Heterogeneous catalysis
Heterogeneous catalysts, also known as heterogeneous catalysts, are used in different phase (Phase) reactions, that is, they are in a different state from the reactants they catalyze. For example: in the production of margarine, solid nickel (catalyst) can convert unsaturated vegetable oil and hydrogen into saturated fat. Solid nickel is a heterogeneous catalyst, and the reactants catalyzed by it are liquid (vegetable oil) and gaseous (hydrogen). A simple heterogeneous catalyzed reaction involves reactants (or zh-ch: substrate; zh-tw: substrate) adsorbed on the surface of the catalyst. The bonds in the reactants are broken and new bonds are generated. Because the bond between the product and the catalyst is not strong, the product leaves the reaction site and other processes. There are many different structures that adsorb and react on the catalyst surface.
Bio catalysis
Enzymes are biocatalysts, organic substances with catalytic ability produced by plants, animals and microorganisms (most proteins. But a small amount of RNA also has a biocatalytic function), formerly known as enzymes. Enzyme catalysis is also selective. For example, starch. Enzymes catalyze the hydrolysis of starch into dextrin and maltose, and proteases catalyze the hydrolysis of proteins into peptides. Living organisms use them to accelerate chemical reactions in the body. Without enzymes, many chemical reactions in the organism will proceed very slowly, making it difficult to maintain life. At a temperature of about 37°C (the temperature of the human body), the working state of the enzyme is the best. If the temperature is higher than 50°C or 60°C, the enzyme will be destroyed and can no longer function. Therefore, biological detergents that use enzymes to decompose stains on clothes are most effective at low temperatures. Enzymes are of great significance in physiology, medicine, agriculture, industry, etc. Currently, the application of enzyme preparations is increasingly widespread.
