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.

The NOx storage reduction (NSR) process is commonly envisaged for the NOx treatment of exhaust gas from lean-burn engine vehicles. NOx are firstly stored on the catalyst, which is periodically submitted to a reducing mixture for few seconds in order to reduce the stored NOx into N2. The on-board reducer is coming from the gasoline/Diesel fuel and, in fact, the NSR catalyst is submitted to a mixture of hydrocarbons, CO and H2 with various compositions depending on the lean/rich step. In this study, the influence of each reducer (C3H6, CO and H2) is evaluated separately, with a special consideration to the N2O selectivity. It is demonstrated that the N2O can be emitted during both lean and rich periods, with varying ratio depending on the considered reducer and the temperature of gas. For instance, at 300°C, a high N2O selectivity is observed when C3H6 is used, and near half of the N2O emission occurs during the storage phase in lean condition.

The efficiency and the selectivity of a model platinum based catalyst supported on a modified ceria-zirconia oxide was evaluated in the NOx storage-reduction (NSR) process at four catalytic scales: powder, (0.5"x1.5") flow-through monolith (FTM) system, small size (1"x2") and full size (5.66"x10") catalysed Diesel Particulate Filter (DPF). The washcoating of the active phase over FTM affects both the NOx storage properties and the NOx reduction step. The reduction step efficiency is especially decreased at low temperatures. It is associated with an incomplete regeneration of the storage sites and with a strong NOx desorption peak during the rich pulses of the NSR process for the FTM supported system. The NOx reduction selectivity is also strongly affected by the upscale, with an important N2O selectivity detected over FTM. The recorded NOx profiles during NSR cycles indicate a probable diffusion limitation. However, same trends were observed for both powder and FTM systems concerning the effect of the reductant mixture, for both NSR efficiency and Ncompounds selectivity. After incorporation of the active phase in the porosity of the DPF, a sharp drop in NOx storage properties and subsequently in NSR efficiency are observed. Supplementary tests suggest that the diffusion from the platinum oxidizing sites to the storage sites is again very affected by the upscale. Finally, the engine bench tests confirm the low DeNOx activity of the DPF system.