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The reduction of soot emission from Diesel engines is an important challenge due to their adverse effects on human health and environment. Therefore, Diesel particulate filters (DPF) are used to trap soot in the gas exhaust lines. DPF must be regenerated periodically and/or continuously by burning-off the soot deposit in order to prevent high back pressure level. Catalysts are used to increase the soot combustion rate. They can be added to the fuel in the form of organometallic precursors or coated on the filter. The nature of the soot-catalyst contact is an important parameter for its oxidation. For this purpose the oxidation of carbon black “CB” used as a model of Diesel soot in presence of a commercial ceria (CeO2) is investigated to gain a better understanding of the effect of the type of contact between the two solids (loose or tight). Different CB/CeO2 mixtures are tested in a fixed bed reactor (mass ratio ranging from 10/90 to 50/50).

Within the framework of the French research program PREDIT, a study was undertaken by ADEME, IFP, LGRE, PSA Peugeot Citroën and Umicore, whose main objective was a better understanding of the NOx storage and reduction phenomena on an aged, sulfated and desulfated NOx-trap. The target of this work was to use the information on catalyst working conditions to optimize catalyst management for a gasoline direct injection engine. The catalysts were characterized on both engine and synthetic gas benches. Aging and poisoning phenomena were studied and a variety of different chemical analytical tools were used. The behavior of two different thermally aged cores was investigated under rich conditions on a synthetic gas test bench. The dependence of the NOx regeneration efficiency of the traps is reported for several operating parameters, including reductant concentrations, durations of the rich pulse and trap loadings.

The behaviour of a NOx storage catalyst in powdered form and containing a storage component based on alkaline metal was investigated under rich conditions. Experiments were conducted in a fixed-bed flow reactor with the space velocity set at 45,000 h-1. From these experiments it was possible to extract the fractional NOx reduction and the efficiency of use of the reductant. With 0.9% CO as a reductant at 350°C, complete utilisation of CO was achieved up to 70% NOx conversion as treatment time was increased. To obtain 90% NOx conversion required longer times, and 23% of the CO did not participate in the reduction of NOX. A reductant balance shows that about 40% of the CO added is used to reduce the catalyst surface when the flow is switched from lean to rich. The ranking of efficiencies of different reductant gases at 350°C gave the following sequence: 0.9% H2 ≈ 0.9% CO > 1285 ppm toluene > 3000 ppm propene ≈ 1125 ppm i-octane > 3000 ppm propane.