What is the catalyst

At present, the role of the catalyst is not fully understood. In most cases, it is believed that the catalyst itself participates in the chemical reaction along with the reactants, reducing the activation energy required for the reaction. Some catalytic reactions are due to the formation of easily decomposable "intermediates", when the decomposition of the catalyst restores the original chemical composition, the original reactants become products. 

Some catalytic reactions are due to adsorption, which can only take place in the most active region of the catalyst surface (called the active center). The larger or more the area of the active center, the more active the catalyst. If impurities are present in the reactant, the activity of the catalyst may be reduced or lost, a phenomenon called catalyst poisoning.

The effect of catalysts on the rate of chemical reactions is very large, and some catalysts can accelerate the rate of chemical reactions to several million times or more. Catalysts are generally selective in that they accelerate only a certain reaction or a certain type of reaction. For example, when heated, formic acid undergoes a decomposition reaction in which half undergoes dehydration and half undergoes dehydrogenation.

HCOOH=H2O+CO

HCOOH=H2+CO2

If solid Al2O3 is used as catalyst, only the dehydration reaction occurs; if solid ZnO is used as catalyst, the dehydrogenation reaction proceeds alone. This phenomenon shows that catalysts with different properties can only accelerate a specific type of chemical reaction process individually. Therefore, we use the selectivity of catalysts to make chemical reactions proceed mainly in a certain direction.

In catalytic reactions, a substance other than the catalyst is often added to enhance the catalytic effect of the catalyst, which is called a co-catalyst. Co-catalysts are extremely important in the chemical industry. For example, the addition of small amounts of aluminum and potassium oxides as co-catalysts in iron catalysts for ammonia synthesis can greatly enhance the catalytic effect of the catalyst.

Catalysts play an extremely important role in the modern chemical industry and are now used in the production of almost half of all chemical products. For example, iron catalysts are used in the production of ammonia, vanadium catalysts are used in the production of sulfuric acid, and different catalysts are used in the polymerization of ethylene and in the production of three major synthetic materials such as rubber from butadiene.

Enzymes, which are proteins with catalytic ability produced by plants, animals and microorganisms, were formerly known as enzymes. Almost all chemical reactions in living organisms take place under the catalytic action of enzymes. The catalytic action of enzymes is equally selective. For example, amylase catalyzes the hydrolysis of starch into dextrin and maltose, protease catalyzes the hydrolysis of proteins into peptides, etc. 

Enzymes are of great significance in physiology, medicine, agriculture, and industry. Currently, enzyme preparations are increasingly used in a wide range of applications.