Low- to Mid-Temperature NH ₃ –SCR with Robust SO ₂ Resistance over Nb–Fe Catalysts Supported on Pre-Sulfided CeO ₂

To address the severe NO x emission problem of marine diesel engines, this study developed a novel sulfur-modified NH 3 –SCR catalyst, NbFe/CeO x S y . Using presulfurized CeO x as a support, this catalyst exhibits higher activity and sulfur resistance. Characterization results show that Nb and Fe are highly dispersed in an amorphous structure, forming abundant defects and a larger specific surface area. NH 3 -TPD and H 2 -TPR results indicate that surface sulfate species introduce additional acidic sites, enhancing redox capacity and promoting NH 3 adsorption and activation. XPS and in situ DRIFTS validated sulfate-mediated redox cycling and enhanced NO 2 adsorption, thereby promoting rapid SCR reactions. SO 2 + O 2 tests showed that presulfation inhibited sulfate accumulation and catalyst deactivation. This study provides a feasible strategy for broadening the catalyst’s operating temperature window and improving its SO 2 resistance, offering valuable guidance for the development of high-performance marine SCR catalysts.