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A commercial NOx-storage catalyst for gasoline applications containing Ba/CeO2/Al2O3, platinum, palladium and rhodium has been sulfated on the engine bench at 390 and 510°C with a nominal exposure of 1.3 g sulfur/liter catalyst. Lower exposures proved too low to have a notable impact on the catalytic performance. At 390°C the sulfur is completely adsorbed while at 510°C only partial adsorption is being observed. Sulfur is mainly deposited at the catalyst inlet thereby shielding the downstream region. Desulfation on synthetic gas bench at 700°C leads to a partial removal of the sulfur. The residual sulfur is more evenly distributed along the length of the catalyst compared to the sulfur profile in the sulfated catalyst. This causes an improvement of the NOx-activity at the inlet side while the NOx-performance at the outlet side decreases after desulfation.

Several diesel powered passenger car manufacturers in the European Union announced recently the future use of catalysed diesel particulate filter systems on their vehicles. The filtration of the exhaust gas is being worked on since several years. Different filter materials and filter designs proved their ability to achieve high filtration efficiencies over the lifetime of the vehicle. The major technological challenge is the periodic regeneration of the filters loaded with the retained diesel particulates. In order to promote filter regeneration, catalytic activation of the accumulated soot is advantageous. Therefore, the first serial application of diesel particulate filter system (diesel oxidation catalyst combined with an uncoated filter substrate) uses catalytically active fuel additives. These systems have been introduced about four years ago and proved to be a viable technology to clean the exhaust gas of passenger car diesel engines.

1 In this paper results obtained with different particulate matter (PM) reduction technologies are presented. Diesel oxidation catalysts (DOC) are well known as a reliable PM reduction technology which can efficiently remove the soluble organic fraction (SOF) but which has no effect on the solid particles in PM. A drawback is that in combination with high sulfur fuel, oxidation of SO2 to SO3 by the DOC can occur, resulting in an increase of PM emissions. An alternative technology that is proven to significantly reduce soot emissions comprises diesel particulate wall-flow filters. High filtration efficiencies of up to 90% and beyond are feasible. The main obstacle is the combustion of the trapped soot. As shown in this paper, the application of a catalyst coating to the filter aids the filter regeneration by lowering the balance-point temperature. The main disadvantages of wall-flow filters are an increase in back-pressure and possible plugging caused by oil-ash accumulations.

Successful system integration of NOx storage catalyst properties into engine management functions implies a profound understanding of the catalyst's performance under transient exhaust gas conditions. During lean operating conditions, this technology achieves a high level of NOx conversion by storing nitrogen oxides reversibly as nitrates. Periodically, the engine control induces a switch to rich, i.e. to reducing conditions, leading to a regeneration of the NOx storage component. The present paper focuses on the investigations of the NOx storage as well as the regeneration process under the described transient reaction conditions for gasoline lean burn applications. In order to study the influence of NOx mass, of the amount of reduction agent offered and of specific regeneration components, experiments were conducted by means of heated exhaust gas oxygen (HEGO) sensors on a model gas as well as an engine test bench.

It is well known that the catalytic efficiency and durability of an automotive catalytic converter can be significantly affected by its design. This paper demonstrates the potential for further improvement in both the durability and efficiency by using a novel catalytic converter concept based on a large frontal area, high cell density substrate. This concept requires that attention be paid to optimization of the flow as well as of the mounting system. The converter design is determined with a computational fluid dynamic (CFD) simulation and the effect of this design on the temperature distribution in the substrate is calculated and measured. Due to this novel converter concept the maximum substrate temperature is reduced, which results in a better aging behavior. This improvement allows a reduction in precious metal content without a loss in efficiency.

1 In recent years Diesel DeNOx catalysts using additional hydrocarbons as reducing agents have been the focus of exhaust aftertreatment. The NOx reduction potential was often limited to 20 - 30 % in the European MVEG-A or the US FTP cycle by just adding a DeNOx catalyst on a vehicle. This result is explained by the fact that the catalyst was treated as a separate item and that the emission reduction strategy was not developed in a system approach. This paper summarizes results regarding the potential of state of the art Diesel DeNOx catalysts fitted to passenger cars and trucks when the exhaust gas system is optimized as a whole. The easiest way for a system approach is the combination of DeNOx catalysts with different working temperatures for NOx reduction. This has been demonstrated by the usage of several base metal catalysts for heavy duty applications. For passenger cars Platinum containing catalysts are strongly favored.

Three European gasoline vehicles, homologated to European Stage II limits, and two US gasoline vehicles, certified to Californian TLEV limits, were evaluated over the new European test cycle for year 2000 standards and the US Federal Test Procedure. Three advanced catalyst technologies were tested on these vehicles, in the original equipment converter position in all but one case, without any additions or changes to the existing emission control system. Prior to testing they were aged on a cycle representing 80,000 km road durability. Up to 30% reductions in emissions were achieved from those for which the vehicles were homologated, at an incremental cost in precious metal of 12 - 23 US$ per liter of catalyst compared to the original converter precious metal value (precious metal prices of 16 July 1996).

To date, several non-SCR catalysts and catalytic systems have been suggested for NOX reduction under oxygen rich (lean) conditions, such as those which exist in diesel engine exhaust gas. However, the performance of such catalysts and catalyst systems is not clear when used on actual diesel engines. This paper reports on experimental results obtained when lean NOx catalysts are applied to diesel engine exhaust. Particularly, the catalysts' NOx performance is examined when secondary hydrocarbons are added as reducing agents directly in the exhaust gas stream. In addition, the effect of different catalyst formulations and secondary hydrocarbon addition on particulate emissions is monitored. Finally, partial system optimization is performed and the applicability of such catalysts and systems to engines operating under the US Heavy Duty Transient Cycle is examined.

The exhaust emissions from stoichiometric gas engines contain CO, Hydrocarbons and NOx besides CO2 and H2O. The Hydrocarbon emissions consist mostly of unburnt methane. Conventional Pt and Rh based three-way catalysts show a good performance for the conversion of CO and NOx at stoichiometric exhaust gas composition, but methane passes almost unconverted through the catalytic converter. At rich exhaust gas composition (Lambda = 0.995) higher conversion rates are achieved for methane, but the efficiency is still not satisfactory for instationary applications. Therefore specific catalyst formulations based on Pd were developed. Model gas reactor and first engine evaluation results are presented. The model gas data indicate that with Pd/Rh catalysts both a wider lambda window and a methane conversion of more than 90% can be achieved. Furthermore catalysts for lean burn applications were investigated.

The general introduction of three-way catalysts in W-Europe starting in 1992 focusses again the attention of car manufacturers on the costs of the precious metals formulation. Three strategies to reduce those costs are discussed: 1. the decrease of the platinum/rhodium loading; 2. the replacement of platinum by palladium and 3. the combination of platinum/rhodium with palladium/rhodium catalysts. The results show that under appropriate conditions of use catalysts with about 20 US$/1 precious metal cost could be a valuable automotive emission control tool.