Rare-earth-doped ceria nanostructures for oxidation of soot with different reactivities: Role of catalyst restructuring and surface acidity in soot-catalyst contact renewal

Catalytic soot oxidation is a key process for particulate filter regeneration, yet catalyst performance is often evaluated using a single soot type, overlooking the strong influence of soot physicochemical properties on oxidation behavior. In this work, the impact of intrinsic soot reactivity on catalytic oxidation was systematically investigated using soot samples with distinct structural, textural, and chemical characteristics. Model flame soots and commercial carbon blacks with different initial reactivity were oxidized over three ceria-based nanostructured catalysts, i.e. pure ceria, equimolar ceria-praseodymia, and equimolar ceria-lanthana. Catalytic activity was assessed under loose and tight contact conditions by temperature-programmed oxidation, complemented by kinetic analysis and stepwise oxidation experiments combined with high-resolution transmission electron microscopy. Regardless of the catalyst, soot reactivity was primarily governed by nanostructural order, as reflected by fringe length, primary particle size, and C/H ratio. Rare earth-doped ceria catalysts exhibited enhanced activity compared to pure ceria, with ceria-lanthana showing the lowest oxidation temperatures in all conditions and the smallest sensitivity to contact degree. This behavior mainly arises from its higher surface acidity, combined with highly abundant surface oxygen species, improved oxygen storage and release capacity, and morphology-induced contact enhancement. HRTEM observations revealed that Ce50La50 dynamically restructures during oxidation, continuously generating new soot-catalyst contact sites that sustain activity under limited-contact conditions. These results highlight the critical interplay between soot properties, catalyst surface chemistry and contact dynamics, thus providing guidance for the rational design of soot oxidation catalysts combining high activity with robustness under operating conditions.