Role of Ce ³⁺ /Ce ⁴⁺ Redox over Ce/TiO ₂ for the Selective Catalytic Reduction of NO with NH ₃

Ce−Ti-based catalysts exhibit high efficiency toward low- and medium-temperature selective catalytic reduction of NO with NH3 (NH3−SCR) owing to the redox flexibility of the Ce3+/Ce4+ pair. However, the intrinsic redox mechanism governing catalytic activity remains insufficiently understood. In this study, dynamic conditions were created to induce NH3 inhibition and N2 conversion inflection (N2 eruption) phenomena, providing deeper insights into the reaction mechanism of NH3−SCR over Ce/TiO2. Operando diffuse reflectance visible (DR-vis) spectroscopy revealed dynamic and reversible changes in the Ce oxidation state under alternating NO + O2 and NH3 atmospheres, directly reflecting the participation of the Ce3+/Ce4+ pair in the reaction. Transient experiments further demonstrate that the re-oxidation of Ce3+ to Ce4+ is closely correlated with the formation of the reactive surface, whereas the reduction of Ce4+ is closely correlated with the release of N2 and H2O. These findings highlight the key role of Ce3+ re-oxidation as the rate-determining step in efficient NOx reduction, offering mechanistic insight and guidance for the rational design of next-generation Ce-based catalysts for deNOx processes.