A recent study published in Engineering presents a significant advancement in the field of diesel vehicle emission control. The research focuses on enhancing the performance of selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) catalysts, which are crucial for reducing harmful nitrogen oxides (NO_x) emitted by diesel vehicles.
Nitrogen oxides from diesel vehicles cause various environmental problems, such as acid rain, haze, and photochemical smog. The NH₃-SCR technology is widely used to remove NO_x from diesel exhaust. However, to meet strict emission standards like Chinese VI and European VI, the NH₃-SCR catalytic converter often works with an upstream diesel particulate filter (DPF). During the DPF’s active regeneration, the NH₃-SCR catalyst is exposed to high temperatures (up to 750–800 °C) in the presence of water vapor, demanding excellent catalytic performance and hydrothermal stability from the catalyst.
In this study, researchers synthesized a tin (Sn)-modified Ce–Nb mixed-oxide catalyst, Ce₁Sn₂Nb₁O_x, using the co-precipitation method. They investigated its NH₃-SCR activity and hydrothermal stability through a series of experiments and characterizations.
The results showed that the addition of Sn remarkably enhanced both the NH₃-SCR activity and hydrothermal stability of the catalyst. Even after hydrothermal aging at 1000 °C, the Ce₁Sn₂Nb₁O_x catalyst achieved more than 90% NO_x conversion at 325–500 °C. In contrast, the unmodified Ce₁Nb₁O_x catalyst and a commercial Cu-SSZ-13 catalyst had significantly lower NO_x conversion rates after hydrothermal aging.
Characterization methods, including N₂-physisorption, X-ray diffraction (XRD), and in-situ high-temperature X-ray diffraction (HTXRD), revealed that Sn addition promoted the formation of the active phase and improved its thermal stability. It inhibited the grain growth of the catalyst, increased the specific surface area and total pore volume, and stabilized the coordination structures of Nb species.
Density functional theory (DFT) calculations further demonstrated that the dispersed CeO_x and NbO_x species on the SnO₂ surface formed efficient and stable NbCeO_x active species, which helped retain redox and acid sites during hydrothermal aging.
This research provides a promising sintering-resistant catalyst for diesel vehicle NO_x emission control, offering a practical solution to meet stringent environmental regulations and improve air quality.
The paper “Remarkable Enhancement of the Activity and Hydrothermal Stability of a CeO₂-Based NH₃-SCR Catalyst by Sn Modification,” authored by Ying Zhu, Jingjing Liu, Guangzhi He, Shaohua Xie, Wenpo Shan, Zhihua Lian, Fudong Liu, Hong He. Full text of the open access paper: https://doi.org/10.1016/j.eng.2024.02.011. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.