#### Article
Some authors have reported improved NO\({}_{\rm x}\) storage capacity (particularly at moderate temperatures, 200-400 \({}^{\circ}\)C) [33] when including ceria as an ingredient in the formulations of these catalysts linked to a high basic character of ceria and to a relevant surface/bulk oxygen mobility. Additionally, the resultant ad-NO\({}_{\rm x}\) species are quite reactive under H\({}_{2}\) or either CO [34]. However, LNT catalysts suffer of some drawbacks, one of them being the use of high-cost noble metals in LNT formulations. Therefore, efforts have been made in order to substitute Pt with other metals; Cu has been proposed as a possible candidate [35; 36; 37; 38]. In addition, interesting properties have been found upon the combination of Cu and ceria; for example, these catalysts present a highly promoted NO oxidation to NO\({}_{2}\) (at low-mid temperatures) and a very high reducibility at low temperatures as well. These improvedcharacteristics have been attributed to a synergistic effect between CuO\({}_{\rm x}\) sites and ceria's surface, which is due to their interfacial interactions that promote redox behavior [39; 40; 41; 42; 43]. The higher capacity of NO and/or NO\({}_{2}\) oxidation has also been exploited by our group, studying copper/ceria-zirconia catalysts in soot combustion processes (under NO + O\({}_{2}\) and under O\({}_{2}\) atmospheres) [44; 45; 46; 47]. Nevertheless, a comprehensive study of the possibilities towards the NO\({}_{\rm x}\) reduction of these catalysts is still lacking. Therefore, the scope of this work involves an interdisciplinary study of the impact that catalysts' formulations (noble metal-free) have on their LNT performance under simulated conditions, thus covering aspects of Materials Science and Chemical Engineering in a highly applied context, related to the development of control strategies for hybrid powertrains and/or the reduction of the impact of cold-start emissions, thus connecting with the aims and scope of the Journal of Applied Sciences and with those of this Special Issue. In a previous work [48], we prepared and fully characterized new LNT catalysts based on Cu/(Ba)/ceria-zirconia components. These catalytic systems were tested in NO\({}_{\rm x}\) adsorption at different temperatures in the range of 150-350 \({}^{\circ}\)C. The catalytic results reported that Cu enhances the NO oxidation activity, which is lowered by the presence of Ba. On the other hand, Ba benefits the NO\({}_{\rm x}\) storage capacity, and consequently, the sample containing both Cu and Ba, with the formulation Cu(2% \(w/w\))/Ba(6% \(w/w\))/Ce\({}_{0.8}\)Zr\({}_{0.2}\)O\({}_{2}\) showing the highest NO\({}_{\rm x}\) storage capacity among the investigated samples. In this study, we complete the analysis of these systems considering only the reduction step, an analysis of the catalysts' formulations (support alone, presence of Cu and/or Ba, loading of Ba), and the effect of the reaction temperature. Finally, some insights into the processes governing NSR operation by this type of noble metal-free ceria-based catalysts are elucidated, focusing on low temperatures and predominant routes of NO\({}_{\rm x}\) reduction with these novel formulations. These elucidations will provide new useful knowledge for the design of subsequent combinations of these systems with other after-treatment technologies.