Chinese name: Catalyst mbth: The function of catalyst: changing the rate of some chemical processes. Also known as: catalyst characteristics, classification, classification method 1, classification method 2, in-depth study, the characteristic catalyst will induce changes in the chemical reaction, which will make the chemical reaction proceed faster or at a lower temperature. We can observe from Boltzmann distribution and energy distribution diagram that the catalyst can make the chemical reactants react through the path with smaller activation energy without changing. Usually at this energy, molecules cannot complete chemical reactions, or it takes a long time to complete chemical reactions. However, in the presence of catalysts, molecules need less energy to complete chemical reactions. Classification and classification method 1. Catalysts are divided into homogeneous catalysts and heterogeneous catalysts. Heterogeneous catalysts appear in the reaction of different phases (for example, solid catalysts are mixed in liquid state), while homogeneous catalysts appear in the same phase (for example, liquid catalysts are mixed in liquid state). Simple heterogeneous catalytic reactions contain reactants (or zh-ch: substrate; Zh-: receptor) is adsorbed on the surface of the catalyst, and the bond in the reactant is very fragile, which leads to the formation of new bonds, but the bond between the product and the catalyst is not firm, which leads to the appearance of the product. At present, many structural positions with different adsorption reaction possibilities are known. When the catalyst and reactants are in uniform gas phase or liquid phase, it is called single-phase catalysis; When the catalyst and reactants belong to different phases, it is called heterogeneous catalysis. Classification method 2 Catalysts that accelerate chemical reactions are called positive catalysts; Catalysts that slow down chemical reactions are called negative catalysts. For example, inorganic acids are often used as catalysts for the hydrolysis of esters and polysaccharides; Sulfur dioxide is oxidized to sulfur trioxide, and vanadium pentoxide is often used as a positive catalyst. The catalyst is solid, and the reactant is gas, forming heterogeneous catalysis. Therefore, vanadium pentoxide is also called catalyst or contact agent. Adding 0.0 1% ~ 0.02% n-propyl gallate to edible oil can effectively prevent rancidity. Here, n-propyl gallate is a negative catalyst (also called moderator or inhibitor). At present, in-depth study, the role of catalysts has not been fully understood. In most cases, it is believed that the catalyst itself and reactants participate in the chemical reaction, which reduces the activation energy required for the reaction. Some catalytic reactions are due to the formation of "intermediate products" that are easy to decompose. When the catalyst was decomposed, the original chemical composition was restored, and the original reactants became products. Some catalytic reactions are due to adsorption and can only be carried out in the most active area (called active center) on the catalyst surface. The larger or more active center area, the stronger the activity of the catalyst. If there are impurities in the reactants, the activity of the catalyst may be weakened or lost. This phenomenon is called catalyst poisoning. Catalysts have a great influence on the chemical reaction rate, and some catalysts can accelerate the chemical reaction rate to several million times or more. Catalysts are generally selective and can only accelerate a certain reaction or a certain type of reaction. For example, when heating, formic acid undergoes decomposition reaction, and half of it is dehydrated and half is dehydrogenated: HCOOH=H2O+CO HCOOH=H2+CO2 If solid Al2O3 is used as catalyst, only dehydration reaction occurs; If solid ZnO is used as catalyst, the dehydrogenation reaction will be carried out separately. This phenomenon shows that catalysts with different properties can only accelerate specific types of chemical reactions. Therefore, we can make use of the selectivity of the catalyst to make the chemical reaction mainly proceed in a certain direction. In the catalytic reaction, people often add another substance to the catalyst to enhance the catalytic effect of the catalyst. This substance is called cocatalyst. Cocatalyst is very important in chemical industry. For example, adding a small amount of aluminum and potassium oxides to the iron catalyst for synthetic ammonia as cocatalyst can greatly improve the catalytic effect of the catalyst. Catalysts play an extremely important role in modern chemical industry. At present, almost half of chemical products use catalysts in the production process. For example, iron catalyst is used in the production of synthetic ammonia, vanadium catalyst is used in the production of sulfuric acid, and different catalysts are used in the polymerization of ethylene and the production of rubber from butadiene. Enzymes are catalytic protein produced by plants, animals and microorganisms, and were previously called enzymes. Almost all biological chemical reactions are carried out under the catalysis of enzymes. The catalysis of enzymes is also selective. For example, amylase catalyzes the hydrolysis of starch into dextrin and maltose, and protease catalyzes the hydrolysis of protein into peptide. Enzymes are of great significance in physiology, medicine, agriculture and industry. At present, the application of enzyme preparation is increasingly extensive.