Indium Catalysts

Indium is a silver-white and slightly bluish metal. Its texture appears so soft that it can be scored with nails. Moreover, its high malleability allows it to be pressed into tablets. Metal indium is mainly used for the production of low melting alloys, bearing alloys, semiconductors, electric light sources and the like. Indium is mainly present in the isomorphism of iron sphalerite, hematite, galena, and other polymetallic sulfide ores. The main oxidation states of indium are +1 and +3, and the main compounds are In₂O₃,In(OH)₃, and InCl₃. These indium compounds are commonly used in photocatalysis and chemical catalysis.

Applications:

• Indium oxide: Indium oxide is an important n-type wide bandgap semiconductor with low resistivity and high catalytic activity. It has a very wide application prospect in the field of optoelectronics, gas sensors and catalysts. At present, indium oxide is used in photocatalysts to degrade organic pollutants and has achieved good research results. For example, some researchers have combined In₂O₃ and TiO₂ to form a new catalytic material that exhibits excellent photocatalytic effects.
• Indium bromide: A significant advantage of indium is that indium metal and its derivatives are less toxic or even non-toxic. Many indium salts such as InBr₃ have very good stability; their crystalline solids are particularly stable to water and air. Some researchers have discovered a new method for synthesizing glycosides under the catalysis of indium bromide. The use of small doses of non-toxic indium bromide as a catalyst can synthesize thioglycosides and oxyglycosides in a simple and efficient manner. The method has the advantages of a wide application range, simple and safe operation, low economic costs, less time required, and environmental friendliness.

Figure 1. Indium bromide catalyzes glycosylation.

• Indium sulfide: In recent years, In₂S₃ has become a leader in many metal sulfide photocatalysts as an excellent visible light catalytic material. This is because In₂S₃ has the proper conduction band valence position, high photosensitivity, stable physicochemical properties, and low toxicity. It is widely used as a catalyst for photocatalytic oxidation of organic pollutants and hydrogen production and has become the most potential visible light catalytic material to replace highly toxic CdS. Some researchers have found that a novel one-dimensional band structure of In₂S₃ can be successfully prepared by a modified solvothermal method. The optical properties of the In₂S₃ nanobelts show that the In₂S₃ has a good photocatalytic degradation effect on methylene blue due to the quantum confinement.
• Indium chloride: Indium chloride exhibits excellent activity in radical reduction and dehalogenation-incorporating addition reaction, and has the advantages of being environmentally friendly and simple post-treatment.

Figure 2. The intramolecular ring-closing reaction catalyzed by indium chloride

Production:

• The indium: The extraction process of indium is mainly based on extraction-electrolysis, which is also the mainstream process technology of indium production in the world today. The principle process is indium containing raw materials → enrichment → chemical dissolution → purification → extraction → back extraction → zinc (aluminum) replacement → sponge indium → electrolytic refining → refined indium.
• Indium compound: There are many methods for preparing indium compounds, such as nitrate decomposition, indium hydroxide decomposition, sol-gel, high-frequency oxygen blowing, carbonic acid decomposition, microemulsion, chemical vapor deposition, dipping, and coprecipitation, etc.

References

1. Li Z J, Liu P L.(1989)."Studies on glycosides VII. Highly stereoselective synthesis of 1-thioglycosides". Synthetic Communications, 20(14): 2169-2175.
2. Nambiar S, Daeuble J F.(1989)."Facile synthesis of silylated thioglycosides".Tetrahedron Letters, 30(17): 2179-2182.