From the powder to the honeycomb. A comparative study of the NSR efficiency and selectivity over Pt–CeZr based active phase

Abstract

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.

Comparative study of the catalytic performance and final surface structure of Co3O4/La-CeO2 washcoated ceramic and metallic honeycomb monoliths

“…In some cases, differences in the catalytic behavior when going from the powder to the monolith have been interpreted in terms of physicochemical features related with the upscaling, e.g. : diffusion limits [5]. However, recent studies have evidenced that the spatial distribution of the different constituents of multicomponent catalysts based on ceria and the compositional features of the surface layer of the corresponding monoliths were significantly influenced by the washcoating process [6].…”

NOx storage and reduction over copper-based catalysts. Part 2: Ce 0.8 M 0.2 O δ supports (M = Zr, La, Ce, Pr or Nd)

“…Cerium oxides have been also studied for NOx removal in Diesel exhausts using the NSR technology [9][10][11], where NOx is stored on the catalyst and a reductant is fed periodically into the exhaust gas stream to reduce the stored NOx species. It has been reported that the NSR performance of Pt/Ceria is improved upon doping ceria with Pr, because Pr accelerates the oxidation of adsorbed NOx species and destabilizes these species when the reductant is fed [12].…”