Effect of reducing agent (C3H6, CO, H2) on the NOx conversion and selectivity during representative lean/rich cycles over monometallic platinum-based NSR catalysts. Influence of the support formulation

Abstract

NOx storage reduction efficiency was investigated on a Pt-10%BaO/Al2O3 model catalyst using a complex gas feed including reductants and oxidants in both lean and rich mixtures. Three representative reductants have been studied, separately and blended: C3H6, CO, H2 and C3H6+CO+H2. The influence of each reductant was evaluated with a special consideration to the N2O selectivity. The reductant /oxidant ratio was kept constant for the lean and the rich gas mixture, respectively. The N2O emission depends on the introduced reductant(s), and the nature of reductant acts differently depending on the temperature. At 200°C, H2 mainly drives the N2O emission, whereas at 300°C, N2O yields is enhanced by C3H6. In addition, it is demonstrated that NOx reduction also occurs during the lean period, leading to significant amount of N2O. In fact, on Pt-10%BaO/Al2O3 catalyst, 70 to 90% of the produced N2O come from the lean phase, except with CO as reductant which does not allow any NOx reduction in lean condition. Results were compared with a platinum/ceria-zirconia-based oxide (Pt/CZ) previously studied. Pt/CZ is generally more active at low temperature (200°C). At 300°C, significant differences appear between the two formulations depending on the used reductant, especially concerning the Ncompound selectivities in the rich pulses.

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

“…15 While both covalent (i.e. surface) and ionic species were observed, the large NOx 16 uptake observed during NSR operation at 300 °C could be mostly related to the replacement 17 of ionic-like carbonates by ionic-like nitrates, probably only in a barium carbonate phase [31]. 18 The sites in the bulk of large barium carbonate particles were yet proposed not to be taking 19 part in the storage.…”

“…95 %, because of the way the experiment was designed: the 16 stream containing NO by-passed the reactor for 30 s over a total cycling period of 10.5 min. 17 The nature of the reduction products was not investigated in details, but gas-phase IR analysis 18 revealed significant proportions of N 2 O, while ammonia was not observed (N 2 is not IR 19 sensitive and cannot be resolved by MS studies in the presence of large concentrations of CO 20 and CO 2 ). The fraction of NOx trapped over the lean period was also calculated using the 21 same equation as that for the NOx conversion but only taking into account the NO fed and 22 NOx in the cell effluent during the lean period: Note that the value of NOx trapped was usually greater than that of NOx conversion because 3 not all the NOx trapped were reduced during the rich phase.…”

“…A description of the NSR technique 5 and a review of the activity of many materials have been reported elsewhere [3]. 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.…”

“…15 The samples were pressed into self-supporting wafers of about 10 mg cm -2 . 16 Feed conditions representative of those occurring in NOx trap converters dedicated to 17 treating the emissions of a Euro 4 Diesel engine were used for the lean and rich phases. The 18 compositions are given in Table 1 indicating that the lean phase exhibited a large O 2 excess.…”

Performance of Cu-ZSM-5 in a Coupled Monolith NSR-SCR System for NOx Removal in Lean-Burn Engine Exhaust

“…H 2 or hydrocarbon from the fuel) is injected, NO x ad-species are released and reduced to nitrogen on Pt. Hydrogen has been found to be the most efficient reductant [4] which can be produced on board by implementing a diesel reformer converter [5]. A good tuning of the operation conditions of both adsorption rate and reduction steps can drive selectively to N 2 and/or NH 3 [6,7].…”