According to the catalytic reaction category, precious metal catalysts can be divided into two categories: homogeneous catalysis and heterogeneous catalysis. The catalyst for homogeneous catalysis is usually a soluble compound (salt or complex) such as palladium chloride, ruthenium chloride, palladium acetate, ruthenium carbonyl, triphenylphosphine ruthenium ruthenium or the like. The catalyst for heterogeneous catalysis is an insoluble solid, and its main form is a metal mesh state and a porous inorganic carrier supported metal state. The application range and amount of wire mesh catalysts (such as platinum mesh and silver mesh) are limited. Most heterogeneous catalysts are supported by noble metal types such as Pt/A12O3, Pd/C, Ag/Al2O3, Rh/SiO2, Pt-Pd/Al2O3, Pt-Rh/Al2O3, and the like. In the whole catalytic reaction process, the heterogeneous catalytic reaction accounts for 80%~90%. According to the shape of the carrier, the supported catalyst can be further divided into fine particles, spheres, columns and honeycombs. According to the main active metals of the catalyst, silver catalysts, platinum catalysts, palladium catalysts and rhodium catalysts are commonly used.