Current Global Status of Rare Earth Elements (REEs) and Their Role as Catalysts in Reducing Air Pollution for Maintaining Environmental Sustainability

Nitrogen oxides (NOx) have numerous negative effects on both the environment and human health. They are major contributors to photochemical smog and acid rain. As a result, researchers are increasingly focused on developing de-NOx technologies. One effective method for removing NOx from the environment is selective catalytic reduction (SCR), with ammonia serving as the reductant (NH3-SCR). Rare earth-based catalysts have emerged as viable options for low-temperature NH3-SCR. Currently Ce-based NH3-SCR catalysts, such as CeO2-TiO2, CeO2-WO3, CeO2-MoO3, Ce-Mn-TiO2, CeO2-MnO2, Ce0.67Zr0.33O2, and CeO2-Fe2O3 have focused significant attention from researchers. The 4f orbitals of rare earth elements (REEs) are devoid of full electron occupancy. This attribute contributes to their distinct catalytic efficacy when employed as catalyst substrates. The oxygen storage capacity of Ce-based catalysts has further enhanced their popularity. Various methods, including microwave, hydrothermal, precipitation and sol-gel techniques, have been used by researchers to prepare catalysts in order to reduce the NOx emission. The paper has covered the impact of the preparation technique on rare earth catalyst performance and the NH3-SCR reaction mechanism to achieve a wide operating temperature. The global production and reserves of rare earth elements (REEs) worldwide have been thoroughly examined, and catalysts for the reduction of NOx emissions in automobiles by Ce and La have been explored.