Zinc Catalysts

At present, metal catalysts are widely used, but their use is limited by the fact that most of the metals used as catalysis are of low reserves, costly, and toxic. Metal zinc is rich in reserves (the twenty-fourth (0.0076%) in the earth's crust) and of high concentration in the ore. At the same time, metal zinc has low toxicity and is relatively environmentally friendly, which makes zinc an attractive catalyst.

Applications:

With all of the advantages mentioned above, metal zinc has been used in a lot of aspects as a catalyst. The specific zinc-catalyzed reaction types are zinc-catalyzed reductions of unsaturated compounds as photocatalysts, zinc-catalyzed oxidation reactions, zinc-catalyzed transformation of carbon dioxide and zinc-catalyzed copolymerization reactions. The most common types of zinc catalysts and their usual applications are as follows:

• Zinc oxide catalyst: Zinc oxide has safe and non-toxic properties, and its photocatalytic properties can be used to inhibit the oxidation of bacteria to achieve anti-corrosion and sterilization purposes.
• Zinc tungstate catalyst: Zinc tungstate (ZnWO₄) is an important member of the tungstate family (AWO₄, A=Zn, Mg, Ca, Ba, Mn, etc.). It was widely studied as an important new semiconductor photocatalyst, photoluminescent material, scintillation material, etc. The crystal structure of ZnWO₄ is shown in Figure 1.

Figure 1. The crystal structure of ZnWO₄

• Zinc silicate catalyst: Zinc silicate can be used as a catalyst to catalyze the oxidation reaction of ozone with the organic macromolecules in sewage, so as to achieve the purpose of purifying water. After catalyzed ozonation by zinc silicate, the proportion of macromolecular organic material in the water is significantly reduced, and the content of small-molecule organic matter is increased.
• Diethylzinc/multiproton catalyst: Diethylzinc/multiproton catalyst refers to a catalytic system formed by a compound containing two or three living hydrogens and diethyl zinc which catalyzes the reaction of carbon dioxide and an epoxy compound to obtain a copolymer. The catalyst model is shown in Figure 2.

Figure 2. Catalyst model for binary catalytic system of diethylzinc and glycerol

• Zinc carboxylate derivative copolymerization catalyst: Such catalysts are prepared from a source of zinc (e.g., ZnO, Zn(OH)₂, Zn(OAc)₂) and with a dicarboxylic acid such as glutaric acid, pimelic acid, acid liver, methyl ester, and the like in toluene. Zinc carboxylate derivative copolymerization catalysts mainly are used to catalyze the polymerization of carbon dioxide and epoxy compounds.

References

1. Weeks, M.E. (1933). 'The discovery of the elements chronology'. J. Chem. Educ. 10, 223-227.
2. M. Ree. (2006). 'New finding in the catalytic activity of zinc glutarate and its application in the chemical fixation of CO₂ into polycarbonates and their derivatives'. Catalysis Taday. 115, 134-145.
3. LIU Y.(2011). 'Ozonation catalyzed by the amorphous zinc silicate for the degradation of pchloronitro-benzene in drinking water'. Applied Catalysis A: General. 403, 112-118.