Study of Ammonia Formation During the Purge of a Lean NO x Trap

Abstract

The aim of this work was to study the formation of ammonia during the regeneration step of a commercial lean NO x Trap catalyst in real conditions. Experiments were carried out on an engine test bench equipped with 2.2 L common rail diesel engine. The aftertreatment system was composed of a commercial NSR monolith catalyst with a volume of 2.2 L. This material was composed of platinum, palladium and rhodium, as active components, with barium oxide and alumina as storage component and support, respectively. Catalytic measurements were carried out at 280°C. Particular attention has been paid to formation of ammonia during the purge using hydrogen and CO as reducing agents. The time dependency of the extent of ammonia formation and the influence of hydrogen concentration were carefully examined. It was observed that the temperature rose in the first step of the regeneration process, after the switch in rich conditions, due to the occurrence of exothermic oxidation (H 2 /O 2 , CO/O 2 ) accompanied with the releasing of available vacant noble metal sites which may provide a route for H 2 and NO dissociation and/or subsequent surface reactions leading to the ultimate formation of ammonia. It was found that ammonia formation strongly depends on the purge duration and on the concentration of the reducing agent available during the purge.

Effects of temperature and rich-phase composition on the performance of a commercial NOx-Storage-Reduction material

“…The 6 understanding of NSR technology has been hampered by the fact that various (usually non-7 realistic) reaction conditions were often used and a very large number of model materials with 8 varying formulations were investigated [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. 9 Several studies have been devoted to commercial NSR materials [23,24,25,26] and in 10 situ FTIR studies [27,28,29,30], but rarely the combination of the two has been reported. One 11 of the difficulties associated with commercial samples is the large number of components 12 present, making difficult the interpretation of in situ/operando IR spectra.…”

Advances in De-NOx Methods and Catalysts for Direct Catalytic Decomposition of NO: A Review

“…Furthermore, nitrates on the storage material will be reduced to NH 3 in O 2 -poor conditions. 48 2.3. Selective Catalytic Reduction (SCR).…”

Mechanistic Aspect of N2O Formation Over Pt–Ba/γ-Al2O3 Catalysts

“…In the case of ammonia as a reductant, previous studies have shown that it behaves similar to H 2 , with the same NO x conversion efficiency [55,56]. On the other hand, some literature data have revealed a difference in NH 3 versus H 2 reactivity towards stored NO x , for different catalyst compositions [50].…”