A substance containing vanadium while performing a catalytic function is referred to as a vanadium catalyst. Vanadium, a silver-gray metal, is chemically stable and cannot be oxidized in air, but is soluble in hydrofluoric acid, nitric acid and aqua regia. Vanadium is abundant in the earth's crust, and the distribution of vanadium is dispersed. The common valence of vanadium is +5, +4, +3, +2, of which the 5-valent state is the most stable. The valence of vanadium in most vanadium catalysts is +5 or +4.
The vanadium catalyst is not a commonly used catalyst, but it still plays a role in the field of organic synthesis because it exhibits excellent catalytic performance in some reactions (such as polymerization reaction and oxidation reaction). In addition, vanadium catalysts are also commonly used in wastewater treatment.
- Oxidation reaction: Vanadium catalysts have a wide range of applications in oxidation reactions and are often used for catalytic oxidation of many organic compounds. Phenol is an organic chemical raw material, which is mainly used for the synthesis of phenolic resin, aniline, alkylphenol, cyclohexanol, bisphenol, adipic acid and other products. In addition, it has a wide range of use in other fields, such as medicine (aspirin, etc.), spices, dyes, pesticides, etc. A VxOy@C catalyst is successfully prepared by directly loading the metal vanadium onto the biomass charcoal. The VxOy@C catalyst can catalyze the oxidation of benzene to produce phenol. VxOy@C is environment-friendly and can be reused, and the VxOy@C catalyst-catalyzed oxidation reaction has the advantage of high selectivity. Sulfoxide compounds are a wide range of intermediates and have a very important role in the organic synthesis of fine chemicals, pharmaceuticals, pesticides, etc. Thioether oxidation is the most direct and most common method for the synthesis of sulfoxides. As a common high-efficiency oxidation catalyst containing vanadium, vanadium acetylacetonate is also used to catalyze the selective oxidation of thioether by hydrogen peroxide. In this reaction, vanadium acetylacetonate is usually supported on a carrier (such as functionalized activated carbon, SiO2 protected magnetic γ-Fe2O3 and ion exchange resin) for solid phase reaction, which has advantages of ease of post-treatment and low contamination.
Figure 1. Vanadium catalyst-catalyzed oxidation reaction
- Polymerization: Many polymers with application value can be prepared by polymerization, and vanadium catalyst is also one of the commonly used catalysts for polymerization. Several vanadium catalytic systems for catalytic polymerization consist of two parts: (1) vanadium compounds such as VCl4, VOCl3, VO(OR)3, VOCl(OR)2, VOCl2(OR) and V(acca)3; (2) Aluminum compounds such as R3Al, R2AlX, R3Al2X3, RAlX2, HAlX2·B and HXAlNR2. For example, when polyacetylene is doped with bromine or iodine, the conductivity is increased to the metal level, which is of high research value. A catalytic system composed of vanadium acetonate, VO(acac)2 and trialkyl aluminum can catalyze the preparation of polyacetylene film by polymerization of acetylene. In addition to catalyzing a single polymerization reaction such as acetylene polymerization, the vanadium catalyst can also catalyze the copolymerization between an alkene and an alkene. For example, vanadium pentoxide is used as a catalytic system to catalyze the terpolymerization of ethylene, propylene and dicyclopentadiene.
Figure 2. Vanadium catalyst-catalyzed polymerization
- Environmental protection: Coking wastewater is derived from high-temperature carbonization of coal, gas purification and recovery of by-products. It has the characteristics of complex composition, poor biodegradability and large organic load. Having the advantages of high efficiency, rapidity and simplicity, Fenton oxidation can effectively treat a variety of refractory organic pollutants. Therefore, it is one of the commonly used methods for treating coking wastewater. Heterogeneous catalysts are often used in Fenton oxidation. As a heterogeneous catalyst, jarosite has the characteristics of large catalytic output, low cost and high efficiency. Jarosite is often used in the Fenton oxidation process to oxidize phenolic compounds and nitrogen-containing heterocyclic compounds in coking wastewater.
- Benmabrouka, Hafsa. (2019), “Vanadium-catalyzed extractive oxidesulfurization of commercial diesel in ionic liquid with combined oxidizing agents.” Petroleum Science and Technology, 37(6), 662-670.
- Fazaeli, Razieh. (2018), “Oxidative Desulfurization of Model Diesel Fuel by Vanadium Granular-Shape Mesoporous (V/GMS) Silica System as Nanocatalyst.” Russian Journal of Applied Chemistry 91(9), 1520-1527.
- Nomura, Kotohiro. (2015), “Olefin Polymerization by Vanadium Complex Catalysts.” Handbook of Transition Metal Polymerization Catalysts (2nd Edition) 313-337.
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