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Future three way catalyst systems are expected to consist of a relatively small start catalyst and a larger volume underfloor catalyst. The main role of the start catalyst is to provide rapid light off. For this purpose, the start catalyst requires relatively small volume with high precious metal loading. Computer simulation is employed to optimize the start catalyst volume with respect to light off performance and precious metal cost. The main role of the underfloor catalyst is NOx removal at elevated temperatures and high space velocities. Due to its large volume, substantial precious metal savings can be realized by the design of a low precious metal underfloor catalyst. The present study focuses on a systematic understanding of NOx breakthrough in three-way catalysts. Special emphasis is on the interaction of the catalyst and the engine management system, especially the lambda control.

The future emission limits for gasoline fuelled passenger cars require more and more efficient exhaust gas aftertreatment devices - the catalytic converter being one essential part of the complex system design. The present paper summarizes the results of several basic research programs putting major emphasis on the application of highly sophisticated three-way catalyst technologies being taylored for the utilization on ultra thin-wall ceramic substrates. In the first part of the investigation the following effects were examined in detail: Different washcoat loadings at constant PGM-loadings Different volumes of catalysts for constant amounts of PGM and washcoat Similar washcoat technologies at different ratios of WC-loading to precious metal concentration in the washcoat.

The present paper highlights the results of a development program focussing on Pt-based three-way catalysts. It is demonstrated that as compared to state-of-the-art Pt/Rh technologies the utilization of advanced washcoat raw materials, new processing methods as well as advanced washcoat systems dedicated to the individual precious metals (PGM) lead to novel catalyst technologies taking better advantage of the lead to novel catalyst technologies taking better advantage of the PGM properties. This yields substantial improvements regarding both aging stability and activity of the catalytic converters. Furthermore, based on the results of a PGM loading study, preferred PGM loadings and ratios were investigated in more detail. In summary, for different application examples it is documented that the newly developed Pt/Rh double layer catalyst is a technical and commercial alternative to the current Pd-based technologies also for high-demanding applications.

There is an increasing interest in running gasoline fueled passenger cars lean of stoichiometric air to fuel (A/F) ratio to improve fuel economy. These types of engines will operate at lean A/F ratios during cruising at partial load and return to stoichiometric or even rich conditions when more power is required. The challenge for the engine and catalyst manufacturer is to develop a system which will combine the high activity rates of a state-of-the-art three way catalyst (TWC) with the ability to reduce nitrogen oxides (NOx) under excess of oxygen. The target is to achieve the future legislation limits (EURO III/IV) in the European Union. Recent developments in automotive pollution control catalysis have shown that the utilization of NOx adsorption materials is a suitable way for reduction of NOx emissions of gasoline fueled lean burn engines.

The trend towards lower exhaust gas temperatures related to the introduction of modern, highly efficient diesel engines for passenger cars in conjunction with new legislative emission regulations will require the development of amended catalyst formulations. Not only excellent performance for carbon monoxide(CO), gaseous hydrocarbons (HC) and diesel particulates is desired but also the capability to additionally reduce nitrogen oxide (NOx) under lean conditions. Generally, as for the latter a passive system, i.e. without addition of secondary fuel, is most wanted but also an active system, i.e. with hydrocarbon enrichment before catalyst, could be successful provided the penalties in fuel consumption can be kept low. The present paper illustrates further progress in the area of diesel catalysts for passenger cars and introduces a novel washcoat formulation comprising zeolites as hydrocarbon adsorption components.

Research programs were completed for the development of improved Pd-containing three-way catalysts, which were targeting on the future emission control standards for passenger cars. The influence of newly developed washcoat components as well as an improved precious metal location in special architectured washcoats on the catalyst performance is demonstrated by model gas and engine tests. The most promising catalyst systems were evaluated on different vehicles in U.S. and E.U. driving cycles. The results obtained in this study clearly indicate the potential of Pd-based technologies to be a cost effective alternative for Pt/Rh converters.

The paper describes research and development work concerning the investigation and optimization of lean NOx catalysts for gasoline and diesel engine applications. The investigations carried out in the laboratory, the engine bench and the chassis dynamometer demonstrate the influence of a number of important catalyst design parameters on the catalyst activity for nitrogen oxide reduction as well as for the conversion of carbon monoxide, gaseous hydrocarbons and in the case of diesel engine exhaust for particulates. In the first part of the paper significant improvements in catalyst activity and durability compared to the first catalyst generation are outlined. A major part of the paper deals with the influence of operation parameters such as space velocity and linear velocity of the reactants in the catalyst. Other aspects discussed are the influence of exhaust gas hydrocarbon component, active site distribution and poisoning elements affecting catalyst activity and durability.

The second stage of the PROCONVE emission legislation, which is effective since model year 1992, was met by various of the Brazilian carmakers through the application of open loop three-way catalysts. As a result of intensive test and development programs, different open loop three-way catalyst designs were selected for ethanol and gasohol fueled vehicles, so as to reach the required emission reduction performance at optimized costs. For the ethanol fueled vehicles, the new washcoats developed allowed precious metal formulations without rhodium. The durability of these systems is supported by the properties of the fuel, since ethanol is basically free of sulphur and lead. For the gasohol fueled vehicles, a Pd/Rh formulation is applied, along with washcoats which guarantee an emission reduction performance in a broad range of A/F engine operation conditions.

The recent decision taken in the USA to further reduce the exhaust emissions from vehicles means a technological challenge for both the designers of engines as well as for the developers of catalytic exhaust aftertreatment systems. A powerful approach is the simultaneous optimization of the engine raw emissions, of the exhaust pipe and catalytic converter design and of the catalyst formulation. The paper aims at demonstrating this by means of two examples. New washcoat formulations for Platinum/Rhodium and for Palladium/Rhodium based monolithic catalysts were developed to reach both an improved conversion performance and a better durability. These catalysts were first evaluated in a model gas reactor using different hydrocarbon species, which were defined by detailed analysis of the vehicle raw emissions during the FTP-75 test cycle. The catalysts were then evaluated on an engine dynamometer, in the fresh and the engine aged state.

Fundamental research work was undertaken to elucidate the mechanism of hydrogen sulfide formation on three-way automotive exhaust catalysts during the lean to rich engine operation sequence and to identify the role of the different catalyst components in this phenomenon. Based upon this knowledge, new catalysts were developed with reduced ability to form hydrogen sulfide by minimizing the storage of sulfur oxides. Engine dynamometer tests confirmed that the suppression of the hydrogen sulfide formation was obtained without loss of catalyst activity or aging stability. The role of the catalyst's age in the hydrogen sulfide formation is discussed. The development presented shows that it is possible to avoid “scavengers” to minimize the emission of hydrogen sulfide from three-way emission control catalysts.