Molybdenum Catalysts

Molybdenum is a kind of refractory rare metal. Because of the strong bond between atoms, its strength is high at both normal temperature and high temperature. It has the characteristics of a small expansion coefficient, high electrical conductivity and good thermal conductivity. It does not react with hydrochloric acid, hydrofluoric acid and alkali solution at room temperature, and is only soluble in nitric acid, aqua regia or concentrated sulfuric acid. It is quite stable in most liquid metals, non-metal slags, and molten glass. Therefore, molybdenum and its alloys have extensive applications and good prospects in important sectors such as metallurgy, agriculture, electricals, chemicals, environmental protection and aerospace, and it has become an important raw material and an irreplaceable strategic substance in the national economy.

Applications:

Due to the unique physicochemical properties of molybdenum materials, in recent years, there have been a lot of reports on optical, electrical and chemical catalytic properties.

• As the chemical catalysts: Iron molybdate has good catalytic properties. Some researchers have synthesized iron molybdate by hydrothermal synthesis and microemulsion method and used them as Fenton-like catalysts to study their catalytic properties. The degradation ability under different pH conditions was also discussed.The results showed that in the acidic environment of pH 2.5~3.5, due to the relatively high rate of hydroxyl radical generation, Fe₂(MoO₄)₃ exhibited strong catalytic properties.

Figure 1. Iron molybdate hydrodesulfurization catalyst

• As the photocatalyst: Some researchers have used γ-Bi₂MoO₆ as a catalyst and found that bismuth molybdate had excellent photocatalytic properties under the action of visible light, which could promote the decomposition of water. The γ-Bi₂MoO₆ nanoparticle prepared by the solution combustion method had high performance of degrading cationic dye under the action of sunlight. The γ-Bi₂MoO₆ flakes were prepared by thermal evaporation deposition method and had good ability to degrade rhodamine B under visible light.

Production:

• Chemical precipitation method: This is a method in which a precipitant is added to a metal salt solution to form a precipitate under certain conditions. Then, the precipitate is subjected to washing, thermal decomposition, or the like to obtain a nanoparticle. Some researchers have synthesized hollow CdMoO₄ microspheres by precipitation in aqueous solution at room temperature. Although the soluble inorganic salt NaCI added during the reaction did not participate in the reaction, it affected the precipitation rate of CdMoO₄ as a complexing aid.
• Hydrothermal method: It refers to a chemical reaction carried out under high temperature and pressure conditions in a sealed pressure vessel (usually a high-pressure reactor) using water as a solvent. Some researchers have used MoO₃ as the molybdenum source and polyethylene glycol (PEG)-400 as the structure-oriented template. The PbMoO₄ nanoparticles with the dendritic structure were prepared by hydrothermal method.
• High-temperature solid phase method: This is a traditional method of preparing molybdenum materials, which is basically used in the early synthesis of molybdenum salts. However, since it is usually necessary to perform high-temperature crystallization treatment, this process tends to cause MoO₃ to volatilize, resulting in excessive crystal grain size and irregular morphology.
• Microemulsion method: The microemulsion method refers to a method of preparing molybdenum through a series of physical-chemical reactions in the droplets of the microemulsion by the reactants. The outstanding advantage of this method is that the prepared material has a uniform particle size distribution.

References

1. Shi Shuyun, Ren Baixiang. (2016). "New heteropoly acid salt photocatalytic degradation of methylene blue dye wastewater". Applied Chemistry. 33(5): 577-582.
2. Li Fengxia, Ma Ronghua. (2016). "Synthesis of γ-Bi2MoO6 composites such as Ding Lingyu and photocatalytic degradation of Congo red". Printing and dyeing auxiliaries. 33(9): 5-9.