Bismuth Catalysts

The bismuth catalyst refers to an elemental bismuth or bismuth compound which has a catalytic function. Bismuth is a brittle, hard, silvery white metal with a pink sparkle. It has a low melting point and expands in volume upon solidification. Bismuth is a group VA element in the periodic table. It is chemically stable and exists in the form of free metals and minerals in nature. The main mineral forms of bismuth metals are Bi₂S₃, Bi₂O₃, Bi₂O₃·mCO₂·H₂O, 3Cu₂S·4Bi₂S₃ and ₂PbS·Bi₂S. Because bismuth metals are non-toxic, they are also called "green metals." Bismuth selenides and tellurides have semiconducting properties.

Figure 1. Bismuth oxide catalyst

Figure 2. Bismuth tungstate catalyst

Applications:

Because of its low price, green non-toxicity and excellent catalytic performance, bismuth catalysts have been widely used in organic synthesis, environmental protection, aerospace and other fields.

• Organic Synthesis: Butadiene is one of the most important synthetic rubber monomers. Industrially, the catalytic process of oxidative dehydrogenation of butene to butadiene is very important. The molybdenum bismuth catalyst is one of the bismuth catalysts. The molybdenum bismuth catalyst is used in the redox reaction, and has the advantages of low cost, good catalytic effect, high yield and the like. Therefore, the molybdenum bismuth catalyst can be industrially used for the preparation of butadiene after oxidative dehydrogenation of butene. In addition, molybdenum bismuth catalysts can also be used industrially to oxidize propylene to acrolein. Yttrium bismuth catalyst is a bismuth oxide material doped with yttrium oxide, which has great application prospects. At present, the main application of this catalyst is to convert methane to ethane or ethylene by oxidative coupling reaction, such as BY25, which is doped with 25% yttrium oxide in bismuth oxide. In the methane oxidation coupling reaction, the catalytic efficiency of the yttrium bismuth catalyst is currently the best, which is 15 times that of the magnesium oxide catalyst and the lithium oxide catalyst. In addition, the yttrium bismuth catalyst can be recycled many times with an average number of 18.
• Environmental Protection: The semiconductor photocatalysis method has become a "green" technology in the complete elimination of various pollutants, especially some azo dyes. A semiconductor photocatalyst that can decompose water to obtain hydrogen energy under ultraviolet or visible light irradiation. It can also be applied to solar cells to convert solar energy into chemical energy, and also to degrade organic pollutants into H₂O and CO₂. Bismuth oxide greatly improves the quantum yield and solar energy utilization rate due to its suitable band gap width and large specific surface area, thereby increasing the degradation rate and efficiency of organic pollutants. Therefore, as a new type of photocatalyst, bismuth oxide can be used for solar water treatment by photocatalytic modification, and has great application in environmental protection. The composite oxide Bi₂WO₆ crystal is a semiconductor having a layered perovskite structure alternately composed of a Bi₂O₂ layer and a WO₄^2-layer, and has high photo-carrier mobility and an energy band structure in response to visible light excitation. In addition, the stability of Bi₂WO₆ is good, and light corrosion is not easy to occur. Bi₂WO₆ can be used as a good photocatalyst for the photocatalytic degradation of rhodiame B.
• Aerospace: In the aerospace industry, lead oxide was once an important catalyst in solid propellants. However, lead oxide is toxic and will directly or indirectly cause harm to researchers or the environment, and lead oxide will generate a large amount of smoke in the engine exhaust, which will cause side effects. As a green metal, bismuth oxide has a very low toxicity. It is an ecologically safe material. As a catalyst in the solid propellant, bismuth oxide avoids the disadvantages of the above lead oxide catalyst for being toxic and generating large smoke. In addition, the nano bismuth oxide material as a catalyst can increase the burning rate of the propellant and lower the pressure.

References

1. Gao, Tengfei. (2019). "Morphology effects of bismuth catalysts on electroreduction of carbon dioxide into formate." Electrochimica Acta 305, 388-393.
2. Popovic, Ksenija D. (2015), "Formic acid oxidation at platinum-bismuth catalysts." Journal of the Serbian Chemical Society 80(10), 1217-1249.
3. Sivakumar, A. (2014), "A review on decolourisation of dyes by photodegradation using various bismuth catalysts." Journal of the Taiwan Institute of Chemical Engineers 45(5), 2300-2306.