Michel Weibel

Current status of modeling lean exhaust gas aftertreatment catalysts

Decreasing emission limits lead to the development of combined aftertreatment systems, consisting of combinations of different catalyst technologies and particulate filters. Modeling such systems can contribute considerably in reducing development time and cost. The methodology for developing catalyst models is reviewed and models for the diesel oxidation catalyst (DOC) with hydrocarbon (HC) adsorption, the NOx storage and reduction catalyst (NSRC) and the urea–selective catalytic reduction system (urea–SCR) are developed. Applications for exhaust aftertreatment system modeling are shown.

Model-Based Approaches to Exhaust Aftertreatment System Development

One major challenge for car manufacturers since several years is to be compliant with the stringent emission standards for internal combustion engines, especially in Europe and in the US. Besides the treatment of standard pollutants like CO, NOx, and HC, the emission of CO2 has gained increasing environmental relevance due to its greenhouse potential. Further reduction of CO2 emissions for lean-burn engines is, in general, correlated with an increase of NOx raw emissions and requires improved aftertreatment systems.

Modelling Inhibition Effects of Short-Chain Hydrocarbons on a Small-Pore Cu-Zeolite NH3-SCR Catalyst

NH3-SCR currently represents the leading technology for NOx abatement from lean exhaust gases, e.g. from diesel engines. Hydrocarbon (HC) slip onto the SCR catalyst can have a negative impact on its DeNOx performance. In order to better understand hydrocarbon poisoning, the influence of different light HCs on the catalytic activity of a small-pore Cu-zeolite has been investigated in a synthetic gas test rig. Based on these data and on further indications from the literature, an existing SCR kinetic model has been extended to represent major effects of light HCs on the behavior of zeolite SCR catalysts. The developed model is able to describe such effects in a simple but effective way.

A PGM-free NOx adsorber + selective catalytic reduction catalyst system (AdSCR) for trapping and reducing NOx in lean exhaust streams at low temperature

Low-temperature operation of urea/NH3-SCR converters, required by recent emission regulations, is challenging due to technological limits related to poor catalytic activity, difficult urea decomposition and undesired ammonium nitrate formation. Herein, we present a novel concept of a catalytic device, which adds a NOx storage functionality to a typical SCR catalyst. This enables capture and storage of NOx in lean exhaust streams already at room temperature, with significant efficiencies under dry conditions, as well as direct reduction of the stored NOx at higher temperatures. The proposed system (AdSCR = adsorption + selective catalytic reduction) is intrinsically different from the well-known existing NOx storage reduction (LNT) + SCR systems. In fact, it is free of PGM materials and does not require lean–rich cycling, being operated just like an SCR catalyst. It has therefore potential advantages both in terms of costs and flexibility of the aftertreatment configuration: in principle, it can be integrated into conventional SCR converters, leading to improved deNOx efficiencies without additional modifications of the aftertreatment architecture.