Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts

Authors:  Stanislava Andonova, Valentina Marchionni, Marta Borelli, Radka Nedyalkova, Luca Lietti, Louise Olsson

Abstract:
To determine the promoting effect of Rh on the overall NO_x storage and reduction (NSR) performance,the studies in the current work were directed toward investigating the storage and release ability over Rh NOx storage BaO-based catalysts compared to Pt. In terms ofthe metal surface dispersion and the ability ofthe noble metals to release oxygen at lower temperatures, the synthesized catalysts were characterized by means of dynamic CO chemisorption (RT) and N₂O dissociation (RT - 773K). The NO_x storage capacity and the thermal stability of the NO_x adsorbed species formed on the surface were analyzed via NO_x storage tests and temperature programmed desorption (TPD) without and in the presence of CO₂ and H₂O. In addition, experiments with lean and rich cycling were conducted at 473, 573 and 673K. The results from the N₂O dissociation experiments showed the superior ability of Rh/Al and Rh/Ba/Al catalysts compared to Pt toward O₂ release from the catalytic surface at lower temperatures. In this work, we show that the presence of Rh into the BaO/γ-Al₂O₃ system has a considerable effect on the spill-over process of NO_x to the precious metal, controlling the subsequent desorption of NO_x to occur at lower temperatures in comparison with that of the Pt catalysts. It is suggested a mechanism of NO_x desorption where the lower temperature of O₂ release from the surface of Rh catalysts could leave a significant number of noble metal sites accessible for adsorption. Thus this could facilitate the rate of spill-over of NO_x from the storage site (the surface sites on γ-Al₂O₃ and those on BaO) to the noble metal and their desorption at lower temperatures. The limited NO_x storage ability of the Rh-based BaO/γ-Al₂O₃ catalysts under leanburn conditions was found to originate from both low NO oxidation activity and NO_x reduction activity, while the main limiting factor for the low NSR performance of the Pt-based catalysts was the limited regeneration ability during rich period.

Keywords:
NO_x storage/reduction
Pt
Rh
BaO noble metal
TPD
N₂O decomposition
CO chemisorption

Published in: Applied Catalysis B: Environmental (Volumes 132–133, Pages 1-552, 27 March 2013)

Publisher: Elsevier  

ISSN Information: 0926-3373

Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts

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