Iridium is a rare precious metal that is expensive on the international market because of its scarce resources. Iridium is one of the densest metals in the known elements and has the highest melting point, high hardness and maximum modulus of elasticity. Moreover, iridium is chemically stable, insoluble in acid, and slightly soluble in aqua regia, chlorine water and molten alkali. In general, noble metal iridium-based catalysts are iridium compounds, noble metal iridium and alloys thereof, and iridium-based supported catalysts. Among them, supported catalysts have the widest application range, that is, noble metal iridium particles are supported on a carrier and fired into a catalyst.
As a precious metal, iridium is mainly used in the preparation of hydrazine decomposition catalysts, automobile exhaust gas purification catalysts, and unsaturated hydrocarbon compound hydrogenation catalysts. In recent years, some progress has been made in the study of catalytic oxidation of iridium complexes. Especially in the catalytic oxidation of iridium complexes, many catalytic systems with good catalytic oxidation effects have been found, and they have high stereoselectivity and chemical selectivity. In addition, the use of iridium complexes as catalysts for catalytic cycloaddition has the advantages of high enantioselectivity, short reaction time and high conversion rate. That has important scientific significance and application prospects to synthesis chiral drugs.
Figure 1. Iridium catalyst catalyzed alkylation reaction.
The iridium-based catalyst is generally prepared by dipping methods, sol-gel methods, and precipitation deposition methods. In some cases, it is also prepared by ion exchange methods and evaporation methods. The support is immersed in an iridium-containing precursor. The precursor of the noble metal iridium is adsorbed on the surface of the support or in the pores, and then subjected to drying, calcination and reduction treatment to carry the supported iridium catalyst.