Performance features of Pt/BaO lean NOx trap with hydrogen as reductant

Abstract

in Wiley InterScience (www.interscience.wiley.com).The performance of a model Pt/BaO/Al 2 O 3 monolith catalyst was studied using H 2 as the reductant. The dependence of product selectivities on operating parameters is reported, including the durations of regeneration and storage times, feed composition and temperature, and monolith temperature. The data are explained in terms of a phenomenological model factoring in the transport, kinetic, and spatio-temporal effects. The Pt/BaO catalyst exhibits high cycle-averaged NOx conversion above 1008C, generating a mixture of N 2 and byproducts NH 3 and N 2 O. The cycle-averaged NOx conversion exhibits a maximum at about 3008C corresponding to the NOx storage maximum. The N 2 selectivity exhibits a maximum at a somewhat higher temperature, at which point the NH 3 selectivity exhibits a minimum. This trend conveys the intermediate role of NH 3 in reacting with stored NOx. Both N 2 and N 2 O are also formed during the storage steps from the oxidation of NH x species produced during the regeneration.

NOx Storage and Reduction for Diesel Engine Exhaust Aftertreatment

“…9b). This agrees with the observation of Clayton et al [91] that nitrogen selectivity increased with the NOx/H2 ratio.…”

“…The hydrogen concentration influences significantly the formation of ammonia at the exit, from 15 ppm NH3 for 0.79% H2 to a maximum of 300 ppm NH3 for 2.32% H2. In fact, the higher H2 concentration in the reduction stream the higher NH3 concentration at the exit, as previously reported [56,78,[87][88][89]91]. These experiments also confirmed the delay in the ammonia detection at the reactor exit related to the beginning of the rich period, as it was observed in the experiments of section 3.…”

“…These authors concluded that the dependence of trapping efficiency on the storage period duration provides a good estimation of the time needed to get a given average conversion during the whole NSR process. More recently, Clayton et al [91] determined the effects of the catalyst temperature, the composition of the rich stream (NO, H2, O2), duration of lean and rich periods and the H2/NO ratio on the average conversion and product selectivity of a commercial Pt-BaO/Al2O3 catalyst. The NOx average conversion resulted maximum at 300 °C, and also the trapping efficiency resulted maximum at the same temperature.…”

Study of N2O Formation over Rh- and Pt-Based LNT Catalysts

“…At variance, N 2 O is a highly undesired by-product in view of its very high global warming potential (nearly 300 times that of CO 2 ). Over fully formulated catalysts, it has been shown that N 2 O formation is apparent both upon switch from lean to rich mode but also during the alternation from rich to lean regime [3][4][5][6][7][8]. It has been suggested that N 2 O formation at the lean to rich transition occurs at the regeneration front, upon reduction of the stored NO x over not fully reduced Platinum-Group-Metal (PGM) sites.…”

Modeling of the desulfation process in NOx storage and reduction catalysts

“…Therefore, the engine is operated in rich mode for a few seconds, in order to remove the stored NO x from the catalyst's surface and subsequently to reduce the released NO x mainly into N 2 and secondarily into N 2 O and NH 3 . The interested reader may find in the literature several experimental studies on the performance of the NSR catalyst as well as simulation studies and kinetic models …”