Sequential sulfidation engineering in Ce-Zr catalysts: Acid site evolution steering reaction pathway optimization for NH3-SCR systems

In this study, a series of Ce-Zr catalysts were synthesized via conventional coprecipitation method, and the mechanistic impacts of sulfation sequences on NH 3 -SCR performance were systematically investigated. The experimental results demonstrated that the Ce-Zr-S catalyst exhibited the optimal NO conversion efficiency (approximately 90 %) at 275 °C. XRD characterization revealed that the synergistic sulfurization strategy effectively facilitated the formation of Ce-Zr solid solutions, which partially suppressed the deactivation of active sites. EPR spectroscopy analysis indicated that the Ce-Zr-S catalyst possessed higher oxygen vacancy concentration compared to other counterparts, which enhanced the Ce 4 + /Ce 3+ redox cycling and subsequently improved oxygen storage capacity (OSC) as well as redox activity. Pyridine-IR, NH 3 -TPD and in situ DRIFTS investigations confirmed that the Brønsted acid site density of Ce-Zr-S was significantly increased. These acid sites functioned as active centers for direct adsorption of NH 4 + species. Importantly, the generated NH 2 NO intermediate was found to promote chemical adsorption/activation of NO molecules, thereby reducing the energy barrier of subsequent reduction steps and ultimately boosting the low-temperature catalytic performance of Ce-Zr-S catalyst. This study investigated the NH 3 -SCR performance optimization mechanism by regulating sulfidation sequences in Ce-Zr catalysts. The Ce/Zr-S configuration preferentially enhanced redox capacity, while Zr/Ce-S focused on increasing acid site density. The co-sulfidized Ce-Zr-S catalyst achieved synergistic optimization through coordinated acid sites and redox capabilities, constructing a structure with high-density oxygen vacancies, Brønsted acid-rich sites, and stable solid solution. Dominated by the Eley-Rideal pathway, the generated -NH 2 intermediates accelerated NH 2 NO formation, effectively reducing reaction energy barriers, ultimately achieving superior low-temperature denitrification performance. • Co-modification of Ce and Zr could enhance the Ce 3+ , O α and acidic sites. • Ce-Zr solid solution could effectively prevent the inactivation of active sites. • Interaction between Ce-Zr and SO 4 2- improve SCR activity due to surface acidity.