Study on the synthesis and modification Cerium oxide nanomaterials
The synthesis of ceria nanomaterials includes precipitation, coprecipitation, hydrothermal, mechanical synthesis, combustion synthesis, sol gel, micro lotion and pyrolysis, among which the main synthesis methods are precipitation and hydrothermal. Hydrothermal method is considered the simplest, most economical, and additive free method. The main challenge of hydrothermal method is to control the nanoscale morphology, which requires careful adjustment to control its characteristics.
The modification of ceria can be enhanced through several methods: (1) doping other metal ions with lower prices or smaller sizes in the ceria lattice. This method can not only improve the performance of the metal oxides involved, but also form new stable materials with new physical and chemical properties. (2) Disperse ceria or its doped analogues onto suitable carrier materials, such as activated carbon, graphene, etc. Cerium oxide can also serve as a carrier for dispersing metals such as gold, platinum, and palladium. The modification of cerium dioxide based materials mainly uses transition metals, rare alkali/alkali earth metals, rare earth metals, and precious metals, which have better activity and thermal stability.
Application of Cerium Oxide and Composite Catalysts
1,The application of different morphologies of ceria
Laura et al. reported the determination of three types of ceria morphology phase diagrams, which relate the effects of alkali concentration and hydrothermal treatment temperature to the final CeO2 nanostructure morphology. The results indicate that the catalytic activity is directly related to the Ce3+/Ce4+ratio and surface oxygen vacancy concentration. Wei et al. synthesized three Pt/CeO2 catalysts with different carrier morphologies (rod like (CeO2-R), cubic (CeO2-C), and octahedral (CeO2-O), which are particularly suitable for low-temperature catalytic oxidation of C2H4. Bian et al. prepared a series of CeO2 nanomaterials with rod-shaped, cubic, granular, and octahedral morphology, and found that catalysts loaded on CeO2 nanoparticles (5Ni/NPs) exhibited much higher catalytic activity and better stability than catalysts with other forms of CeO2 support.
2.Catalytic degradation of pollutants in water
Cerium oxide has been recognized as an effective ozone oxidation catalyst for the removal of selected organic compounds. Xiao et al. found that Pt nanoparticles are in close contact with CeO2 on the catalyst surface and undergo strong interactions, thereby improving the ozone decomposition activity and producing more reactive oxygen species, which contribute to the oxidation of toluene. Zhang Lanhe and others prepared doped CeO2/Al2O3 catalysts. Doped metal oxides provide a reaction space for the reaction between organic compounds and O3, resulting in higher catalytic performance of CeO2/Al2O3 and an increase in active sites on the catalyst surface
Therefore, many studies have shown that cerium oxide composite catalysts can not only enhance the degradation of recalcitrant organic micro pollutants in the field of catalytic ozone treatment of wastewater, but also have inhibitory effects on the bromate produced during the ozone catalytic process. They have broad application prospects in ozone water treatment.
3,Catalytic degradation of volatile organic compounds
CeO2, as a typical rare earth oxide, has been studied in multiphase catalysis due to its high oxygen storage capacity.
Wang et al. synthesized a Ce Mn composite oxide with a rod-shaped morphology (Ce/Mn molar ratio of 3:7) using a hydrothermal method. Mn ions were doped into the CeO2 framework to replace Ce, thereby increasing the concentration of oxygen vacancies. As Ce4+is replaced by Mn ions, more oxygen vacancies are formed, which is the reason for its higher activity. Du et al. synthesized Mn Ce oxide catalysts using a new method combining redox precipitation and hydrothermal methods. They found that the ratio of manganese and cerium played a crucial role in the formation of the catalyst and significantly affected its performance and catalytic activity. Cerium in manganese cerium oxide plays a crucial role in the adsorption of toluene, and manganese has been shown to play a crucial role in the oxidation of toluene. The coordination between manganese and cerium improves the catalytic reaction process.
4.Photocatalyst
Sun et al. successfully prepared Ce Pr Fe-0 @ C using co precipitation method. The specific mechanism is that the doping amount of Pr, Fe, and C plays an important role in photocatalytic activity. Introducing an appropriate amount of Pr, Fe, and C into CeO2 can greatly improve the photocatalytic efficiency of the obtained sample, because it has better adsorption of pollutants, more effective absorption of visible light, higher formation rate of carbon bands, and more oxygen vacancies. The enhanced photocatalytic activity of CeO2-GO nanocomposites prepared by Ganesan et al. is attributed to enhanced surface area, absorption intensity, narrow bandgap, and surface photoresponse effects. Liu et al. found that Ce/CoWO4 composite catalyst is a highly efficient photocatalyst with potential application value. Petrovic et al. prepared CeO2 catalysts using constant current electrodeposition method and modified them with non thermal atmospheric pressure pulsating corona plasma. Both plasma modified and unmodified materials exhibit good catalytic ability in both plasma and photocatalytic degradation processes.
Conclusion
This article reviews the influence of synthesis methods of cerium oxide on particle morphology, the role of morphology on surface properties and catalytic activity, as well as the synergistic effect and application between cerium oxide and dopants and carriers. Although cerium oxide based catalysts have been widely studied and applied in the field of catalysis, and have made significant progress in solving environmental problems such as water treatment, there are still many practical problems, such as unclear cerium oxide morphology and loading mechanism of cerium supported catalysts. Further research is needed on the synthesis method of catalysts, enhancing the synergistic effect between components, and studying the catalytic mechanism of different loads.
Journal author
Shandong Ceramics 2023 Issue 2: 64-73
Authors: Zhou Bin, Wang Peng, Meng Fanpeng, etc