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Future US emissions limits are likely to mean a sophisticated nitrogen oxide (NOx) reduction technique is required for all vehicles with a diesel engine, which is likely to be either NOx trap or selective catalytic reduction (SCR) technology. To investigate the potential of SCR for NOx reduction on a light duty vehicle, a current model vehicle (EUII M1 calibration), of inertia weight 1810 kg, was equipped with an urea-based SCR injection system and non-vanadium, non-zeolitic SCR catalysts. To deal with carbon monoxide (CO), hydrocarbon (HC) and volatile organic fraction (VOF), a diesel oxidation catalyst was also incorporated into the system for most tests. Investigations into the effect of placing the oxidation catalyst at different positions in the system, changing the volume of the SCR catalysts, increasing system temperature through road load changes, varying the SCR catalyst composition, and changing the urea injection calibration are discussed.

The low exhaust gas temperatures experienced on light duty Diesel vehicles present a very challenging environment for the successful operation of catalytic aftertreatment. To meet the future more severe legislation, Diesel engines are being developed with greater combustion efficiencies and advanced fueling control. These engine developments may produce lower particulate matter (PM) and nitrogen oxides (NOx) emissions, but increased hydrocarbon (HC) and carbon monoxide (CO) emissions may occur. As a result of these engine changes exhaust gas temperatures may reduce still further. These factors demand catalysts with high oxidation activity at low temperatures. This paper reviews oxidation catalyst technology developed for light duty Diesel vehicles and the factors affecting their performance. Results obtained on synthetic gas rigs, bench engines and vehicles are presented. A discussion oh the effect of the level of sulfur (S) present in Diesel fuel on aftertreatment is given.

The lower temperatures encountered with European Stage III/IV turbo charged direct injection (DI) Diesel engines with additional features such as cooled exhaust gas recirculation (EGR), compared to Stage II engines, means that modern light duty Diesel engine exhaust gas will rarely exceed temperatures of around 550° - 650°C under full load conditions, and under normal driving conditions, temperatures as low as 120°C will be common. The development of high activity Diesel oxidation catalysts (DOCs) having good low temperature performance is therefore key for achieving hydrocarbon (HC) and carbon monoxide (CO) conversions to meet Stage III and IV legislation. It is shown that extended operation of conventional DOC technology, at the lower temperatures encountered on modern Diesel engines, introduces an important mechanism of catalyst deactivation by accumulation of soot/coke and associated sulfur.

The drive towards improved fuel economy and lower emissions for Diesel vehicles requires the development of catalysts capable of converting not only carbon monoxide (CO) and hydrocarbon (HC), but also particulate matter (PM) and nitrogen oxides (NOx) in a lean exhaust environment. This paper reviews the approaches that are being considered for this purpose, for light duty Diesels, together with factors that may influence catalyst performance such as components in the fuel and quality of the lubricant.

Reduction of nitrogen oxides in Diesel exhaust gas is a challenging task. This paper reports results from an extensive study using Pt-based catalysts involving synthetic gas activity testing (SCAT), engine bench testing and tests on passenger cars. Preliminary SCAT work highlighted the importance of Pt-dispersion, and both SCAT and bench engine testing yielded comparable NOx conversions under steady state conditions at high HC:NOx ratios. On passenger cars in the European cycle without secondary fuel injection NOx conversion was lower than obtained in the steady state tests. Better conversion was obtained in the FTP cycle, where secondary injection was employed. Higher HC:NOx, ratios and more favourable temperature conditions which were present in the exhaust contributed to this higher conversion.

In response to the demands for catalysts to meet the emerging autocatalyst market in Europe, Johnson Matthey Catalytic Systems Division (Europe) has designed and commissioned an improved catalyst evaluation facility. The aim of the project was to provide a more efficient means of screening catalyst technology from formulation development stages to pre-production validation, against a wide variety of synthetic mileage accumulation cycles. This paper describes how the extensive use of computer technology interfaced with modern analytical instrumentation has achieved a significant increase in productivity. This includes the ability to carry out evaluations unattended under full computer control.

Metal substrates have been available as catalyst supports for the past 10 years but their use has been limited to a few specialised applications, for example as light-off or starter catalysts for large cars. The emergence of Europe as an autocatalyst market with differing requirements has prompted a reassessment of the potential for metal supported catalysts. This paper will review much of the work conducted; in particular washcoat adhesion, hot-shake and high speed durability as well as reporting the results of a volume/cell density parametric study, comparing metal supported catalysts with ceramic supported catalysts on vehicles.

The performance of a vehicle equipped with a single bed three way catalyst has been monitored during a 50,000 mile durability test at maximum speed (168 ktnph). Subsequently, emissions as a function of average speed were studied in baseline, durability catalyst and dynamometer aged catalyst conditions.

THE DEVELOPMENT of a novel precious metal catalyst system supported on a metal substrate is outlined. The key nature of the metallic species is demonstrated. A high performance alloy, FECRALLOY STEEL®, is identified as a suitable material. Conversion of this alloy into a durable catalyst using a proprietary pre-treatment to render it compatible with existing catalysts and production procedures is discussed. The flexibility in processing with respect to key design features e.g. cell density, is emphasised. The influence of support variables such as volume, cell density etc., on the performance of an oxidation catalyst is reported together with comparable data for ceramic supported catalyst. It is shown that at zero hours, equivalent performance, at no power loss penalty relative to ceramics, can be secured by judicious choice of cell density/volume combinations. Such equivalence can be achieved with significantly lower volumes and significant scope exists for further optimisation.