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 NOx with NH3 (NH3-SCR) catalysts, which are crucial for reducing harmful nitrogen oxides (NOx) 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 NOx 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, Ce1Sn2Nb1Ox, 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 Ce1Sn2Nb1Ox catalyst achieved more than 90% NOx conversion at 325–500 °C. In contrast, the unmodified Ce1Nb1Ox catalyst and a commercial Cu-SSZ-13 catalyst had significantly lower NOx 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 CeOx and NbOx species on the SnO2 surface formed efficient and stable NbCeOx active species, which helped retain redox and acid sites during hydrothermal aging.
This research provides a promising sintering-resistant catalyst for diesel vehicle NOx 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
