Bernd Krutzsch

Removal of nitrogen oxides from the exhaust of a lean-tune gasoline engine

There is an increasing interest in running passenger car engines lean of the stoichiometric air to fuel ratio (A/F) to improve fuel economy. One method being considered by vehicle manufacturers is to operate lean A/F (excess air) during cruising and return to stoichiometric operation when more power is required. The challenge for the catalyst manufacturer is to supply a product for this vehicle which will reduce NOx emissions from both lean and stoichiometric operating points to below probable EC tier III legislative limits. A technique has been developed where NOx is stored on an adsorbing catalyst while the engine runs lean. Upon switching to a short rich biased stoichiometric excursion the adsorbed NOx is released and reduced by precious metal components on the catalytic system. Selected adsorber catalysts were tested on both simulated exhaust gas and a standard bench engine with secondary air injection. The results suggest an adsorbing process whereby NO is oxidized to NO2 on Pt under lean conditions and the latter is subsequently adsorbed on an adsorbent material as a surface nitrate species. Upon return to a stoichiometric A/F ratio this species decomposes and NOx is released and subsequently reduced. The adsorber was also tested on a bench prototype lean tune engine. The results indicate an averaged NOx conversion of more than 90% over a test cycle in which the A/F ratio is cycled between lean operation and a rich biased stoichiometry.

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.

Selective NO reduction by propane and propene over a Pt/ZSM-5 catalyst: a transient study of the reaction mechanism

Abstract The selective reduction of nitric oxide by propane and propene in an excess of oxygen has been studied over a Pt/ZSM-5 catalyst to elucidate the role of the reducing hydrocarbons in the reaction mechanism. Temperature-programmed reaction (TPR) and transient studies using the temporal-analysis-of-products (TAP) reactor have been performed. Propene is found to be the more efficient reductant compared to propane at T ⩽ 600K. Mechanistic studies demonstrate that even in an excess of oxygen carbon-containing species, formed from propene, are adsorbed on the catalyst, which further react with nitric oxide to N2, N2O and CO2; no such intermediates are formed from propane, giving rise to its far lower reduction efficiency. It is concluded that the main reaction pathway over Pt/ZSM-5 involves a surface reaction between propene-derived adsorbates and NO or, possibly, NO2. Catalytic surface reduction by hydrocarbons, followed by NO decomposition on reduced platinum sites, is proposed as a second, minor, mechanistic pathway at low reaction temperatures (T ⩽ 600K).