FT-IR study of NO X storage mechanism over Pt/BaO/Al2O3 catalysts. Effect of the Pt–BaO interaction

Abstract

NO x storage mechanism over a model NSR catalyst has been analysed by means of in-situ FTIR. The results indicated that a two-step mechanism involving nitrite formation, without requirement of NO evolution to NO 2 , followed by oxidation to nitrate species, being both steps assisted by O 2 , would describe the overall process at 350°C. This mechanism could be also extended to a wider temperature range. The interaction between Pt and Ba sites was crucial in this mechanism, since spillover process of oxidising agents appeared to play a key role. NO 2 direct interaction with BaO surface may also occur, but this process was only dominant on Ba sites away from Pt interaction.

NOx Storage and Reduction for Diesel Engine Exhaust Aftertreatment

“…Bridged nitrites situated at 1220 cm -1 [66] were dominant when the adsorption was carried out below 250 °C, whereas the dominant species became ionic nitrates (asymmetric and symmetric modes of monodentate nitrates) located at 1332 and 1414 cm -1 [69] for temperatures above 250 °C. This shift in the adsorption mode from nitrites to nitrates with temperature had been already reported in the literature [62,63,66,67,70]. All spectra included in Fig.…”

Effect of Co addition to Pt/Ba/Al2O3 system for NOx storage and reduction

“…Furthermore, Ba sites located in proximity to Pt play an important role during the trap process. A spill-over mechanism has been proposed to explain the effective adsorption, which suggests that both oxygen and NO/NO 2 could easily migrate from a Pt site to a nearby Ba site, thus improving the adsorption efficiency [16,17]. Recent studies [18] have also demonstrated that the impregnation procedure of Pt or Ba influenced NSR performance, which is both interesting and effective in the optimization of catalyst preparation methods.…”

Effect of the Incorporation Order of Pt- and Ba-Precursors on the Structure and Catalytic Performance of NSR Catalysts

“…Clayton et al [12] already observed this phenomenon, pointing out that the NO X supply to Pt sites was the limiting step at low temperatures. It is also well known that the proximity between Pt and Ba assists in forward and reverse spillover of species between Pt and BaO, which are of great importance in both storage and reduction processes [13,14]. Particularly, it has been proven that specific pretreatments could result in a better Pt-Ba proximity which leads to an increase of the NO X uptake [2].…”