Classification and characteristics of catalysts

There are many types of catalysts, which can be classified into liquid catalysts and solid catalysts according to the state; homogeneous catalysts and multiphase catalysts according to the phase state of the reaction system; homogeneous catalysts include acid, base, soluble transition metal compounds and peroxide catalysts. 

Multi-phase catalysts include solid acid catalysts, organic base catalysts, metal catalysts, metal oxide catalysts, complex catalysts, rare earth catalysts, molecular sieve catalysts, biocatalysts, nano catalysts, etc.; according to the reaction type, they are divided into polymerization, condensation, esterification, acetalization, hydrogenation, dehydrogenation, oxidation, reduction, alkylation, isomerization, etc.; according to the role size, they are also divided into main catalysts and co catalysts.

Homogeneous catalysis

A reaction in which the catalyst and the reactants are in the same phase and there is no phase boundary is called homogeneous catalysis, and a catalyst that can act as a homogeneous catalyst is a homogeneous catalyst. Homogeneous catalysts include liquid acid and base catalysts, solid acid and base catalysts, soluble transition metal compounds (salts and complexes), etc. Homogeneous catalysts act independently as molecules or ions, with homogeneous active centers and high activity and selectivity.

Multiphase catalysis

Multiphase catalysts, also known as non-homogeneous catalysts, are used in reactions with different phases (phases), i.e., in different states from the reactants they catalyze. For example, in the production of margarine, solid nickel (catalyst) enables the conversion of unsaturated vegetable oil and hydrogen to saturated fat. Solid nickel is a multiphase catalyst and the reactants catalyzed by it are in liquid (vegetable oil) and gaseous (hydrogen) states. 

A simple non-homogeneous catalytic reaction involves processes such as adsorption of reactants (or zh-ch:substrate; zh-tw:acceptor) on the surface of the catalyst, the creation of new bonds within the reactants due to breakage, but then the release of the products from the reaction sites because the bonds between the products and the catalyst are not strong. Many different structures on the catalyst surface where adsorption and reactions occur are known.

Biocatalysis

Enzymes are biocatalysts, organic substances produced by plants, animals and microorganisms with catalytic ability (the majority of proteins. However, a small amount of RNA also has biocatalytic function), formerly known as enzymes. The catalytic action of enzymes is equally selective. For example, starch. Enzymes catalyze the hydrolysis of starch into dextrin and maltose, proteases catalyze the hydrolysis of proteins into peptides, etc. Living organisms use them to accelerate chemical reactions in the body. Without enzymes, many chemical reactions in living organisms would proceed very slowly and be difficult to sustain life. Enzymes work best at a temperature of about 37°C (the temperature of the human body). 

If the temperature is higher than 50°C or 60°C, the enzymes are destroyed and can no longer function. Therefore, biological detergents that use enzymes to break down stains on clothing are most effective when used at low temperatures. Enzymes are of great significance in physiology, medicine, agriculture, and industry. Currently, enzyme preparations are increasingly being used.