Precious metal catalyst: precious metal catalyst that can alter the rate of chemical reaction without being involved in the final product. Almost all precious metals can be used as catalysts, but platinum, palladium, rhodium, silver and ruthenium are commonly used, especially platinum and rhodium. Their d electron orbitals are not filled, the surface is easy to adsorb reactants, and the strength is moderate, conducive to the formation of intermediate "active compounds", with high catalytic activity, but also with high temperature resistance, oxidation resistance, corrosion resistance and other comprehensive excellent characteristics, become the most important catalyst materials. Precious metal catalysts have a close relationship with environment and public health for national economic construction. For example, the development of chemical industry and petroleum processing industry is based on catalytic reaction, and more than 85% of the world's chemical industry is related to catalytic reaction. At the beginning of 1930-1980. The chemical industry has revolutionized 63 of the chemical sector's major products and 34 processes, with more than 60 percent of the products and 90 percent of the processes based on catalytic processes. Commercialization of a new catalytic process requires significant investment, and catalyst research has helped minimize this time lag over the course of 10,115 years. The public is increasingly concerned about the environmental pollution caused by chemicals and industrial emissions and the state of the living space for treatment. Many modern, low-cost and energy-saving environmental technologies are related to catalytic technologies. Automobile exhaust emission control is an international strategic issue. The catalyst has been well developed and applied in the United States and some European countries. In addition, the biological degradation of organic waste, the treatment of soil, sewage and groundwater pollutants, and the purification of petroleum pollutants are all inseparable from noble metal catalysts. The three major strategies for reducing the environmental impact of chemicals today are: minimizing waste, reducing emissions, and taking remedial measures, in which precious metal catalysts play a significant role. A brief history: in 1831, British phillips put forward the contact method using platinum as catalyst to produce sulfuric acid. By 1875, this method was industrialized, which was the earliest industrial application of precious metal catalyst. Since then, the industrial application of noble metal catalyst layer. In 1913, platinum-mesh catalyst was used for ammonia oxidation to produce nitric acid. 1937 Ag/Al2O3 catalyst for the oxidation of ethylene to ethylene oxide; In 1949, Pt/Al2O3 catalyst was used for reforming petroleum to produce high quality gasoline. Pdcl2-cucl2 catalyst was used to oxidize ethylene to acetaldehyde in 1959. Rhodium complex catalyst for low pressure carbonyl synthesis of acetic acid with methanol was developed in the late 1960s. Since 1974, precious metal catalysts (mainly platinum, supplemented by palladium and rhodium) for automobile exhaust purification have been widely used and rapidly developed into the largest amount of precious metal catalysts. Precious metal catalysts have been developed and applied for more than 100 years (from 1875 to 1994), and their development momentum has been unfading. New varieties, new preparation methods and new application fields keep emerging, and relevant basic theories keep improving. With the continuous progress of science and technology, precious metal catalysts will continue to play an important role in some new fields. Of course, because precious metals are scarce and expensive, people are also developing non-precious metals or low-content precious metals catalysts. Noble metal catalysts can be divided into homogeneous catalysis and heterogeneous catalysis. Homogeneous catalysts are usually soluble compounds (salts or complexes), such as palladium chloride, rhodium chloride, palladium acetate, carbonyl rhodium, and triphenylphosphine carbonyl rhodium. The catalyst used for multiphase catalysis is insoluble solid, and its main form is wire mesh state and porous inorganic carrier supported metal state. Wire mesh catalyst (such as platinum mesh, silver mesh) application range and amount of limited. Most multiphase catalysts are supported by precious metals, such as Pt/A12O3, Pd/C, Ag/Al2O3, Rh/SiO2, pt-pd/Al2O3, etc. In the whole process of catalytic reaction, heterogeneous catalytic reaction accounted for 80% ~ 90%. According to the shape of the carrier, supported catalyst can be divided into granular, spherical, columnar and honeycomb. Homogeneous catalysts are usually composed of simple compounds. The supported catalysts for heterogeneous catalysis are usually composed of active metal components, supporting catalysts and supports. A cocatalyst is a small amount of material added to a catalyst that has little or no activity but improves the performance of the catalyst. The carrier is the dispersant or support of the active component of the catalyst. The main function of the carrier is to increase the effective surface of the catalyst, provide suitable pore structure, and ensure sufficient mechanical strength and thermal stability. Common catalyst supports are Al2O3, SiO2, porous ceramics, activated carbon, etc. Different types of catalysts have different preparation methods. The preparation of catalysts for homogeneous catalysis is mainly to obtain the required compounds and organic complexes by chemical methods. The preparation of multiphase catalysis with carrier free catalyst is first smelted into alloy by fire, then by drawing and weaving. The preparation of carrier catalyst is complex. Generally, the carrier raw materials are processed into a certain shape (such as spherical, columnar and honeycomb shape) through the process of dosing, shaping and burning, and then the noble metal active components and auxiliary catalysts are loaded by the impregnation method, and finally they are made by reducing roasting. The catalytic properties of precious metals precious metals catalysts have been used in many chemical reactions especially platinum group metals with high catalytic activity. At the l6th organic reaction catalyst conference held in Atlanta in 1996, 70% of the papers on pg-group metal catalysts accounted for _8J. Why did noble metal catalysts have such a good catalytic effect? Precious metals is a transition metal element, with empty d band track, which has a molecule in the reaction of electrophilic and nucleophilic, REDOX ability, such as nature, due to its diversity, variety and high in activity, through the ligand or other modulation effect of metal ions, the reaction activation or activation of molecules adsorption and stable, so is composed of transition metal catalysts.