Revealing the Roles of Cu/Ba on Ce-Based Passive NOx Adsorbers

Abstract

At present, passive NOx adsorbers (PNAs) represent one of the most effective technologies for addressing NOx emissions from diesel engines during cold-start periods. Conventional PNAs, which primarily consist of noble metals (such as Pt, Pd, and Ag) loaded on metal oxides or zeolites, share the common drawback of high production costs. Consequently, developing low-cost PNAs with outstanding NOx storage performance remains a significant challenge. In this study, a series of CuxBa5Ce adsorbents were synthesized using the impregnation method, and a monolithic adsorbent was employed to evaluate NOx storage and release performance. Techniques such as XRD, UV-Vis DRs, H2-TPR, XPS, and in situ DRIFTs confirmed the crucial roles of Cu and Ba in NOx storage and release. Specifically, the incorporation of Cu into CeO2 enhanced NOx storage performance. Moreover, in the Cu3Ba5Ce adsorbent, the addition of Ba not only introduced new storage sites and altered the stability of NOx adsorption species but also helped prevent the aggregation of CuO, thereby prolonging the complete NOx storage duration and satisfying desorption temperature requirements. The Cu3Ba5Ce adsorbent exhibited the most favorable NOx storage performance, including a complete NOx storage time of 135 s and a NOx storage efficiency exceeding 50% at 80 °C over a 10 min period. While PNAs loaded with noble metals, such as Pd/CeO2 and Pt/CeO2, exhibited NOx storage efficiencies below 50% after adsorbing for 5 min at 80 °C. Therefore, this research offered a crucial strategy for developing non-noble-metal-loaded, Ce-based PNAs.

Revealing the Roles of Rh in Inhibiting “NOx Puff” on the Cu/Ba-CeO2 Catalyst during the Process of Lean NOx Trap

“…Therefore, the XRD results showed that no significant differences were observed before and after the addition of Rh. In agreement with the previous report, 25 UV−vis DRs absorption bands belonging to (Cu−O−Cu) 2+ clusters were clearly observed at 430 nm from Cu5Ba5Ce, as shown in Figure 2b. It is worth noting that a significant red shift of the absorption band and a gradual shift to a broader shoulder peak could be observed after the loading of Rh, which have been due to the fact that the introduction of Rh promoted the concentration of Cu 2+ , thereby increasing the number of (Cu− O−Cu) 2+ clusters.…”

“…As shown in Figure a, the main X-ray diffraction (XRD) diffraction peaks were assigned to the fluorite cubic structure of CeO 2 on both catalysts. Based on the previous work, the diffraction peak attributed to “LT-BaCO 3 ” (2θ = 23.9°) with excellent NO x storage performance was observed on both catalysts. No diffraction peaks associated with the Cu and Rh phases were observed.…”

“…The low-temperature NO x adsorption performance was obviously enhanced on Ce-based passive adsorbents by Cu loading in our previous study . It was still observed that using CuxBa5Ce as an LNT catalyst exhibited a pronounced “NO x puff” during the rich-burn period.…”

“…The low-temperature NO x adsorption performance was obviously enhanced on Ce-based passive adsorbents by Cu loading in our previous study. 25 It was still observed that using CuxBa5Ce as an LNT catalyst exhibited a pronounced "NO x puff" during the rich-burn period. In this work, it was attempted to improve the reduction activity of NO x by adding Rh to Cu5Ba5Ce, and "NO x puff" would be correspondingly inhibited.…”

Effect of SO2 introduction into CeO2 on its surface acidity and redox property for the selective catalytic reduction of NO with NH3

“…58 Pei et al showed that surface adsorbed oxygen acted as reactive oxygen and favored the formation of nitrogen dioxide to promote catalytic activity. 59 The O α significantly assisted in the increase in S–Ce activity. After sulfating H–Ce, the proportion of the O α /(O α + O β ) ratio of the H–S–Ce catalyst was greater compared to that of H–Ce.…”