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Catalyzed soot filters are being fitted to an increasing range of diesel-powered passenger cars in Europe. While the initial applications used silicon carbide wall-flow filters, oxide-based filters are now being successfully applied. Oxide-based filters can offer performance and system cost advantages for applications involving both a catalyzed filter with a separate oxidation catalyst, and a catalyzed filter-only that incorporates all necessary catalytic oxidation functions. Advanced diesel catalyst technologies have been developed for alternative advanced oxide filter materials, including aluminum titanate and advanced cordierite. In the development of the advanced catalyzed filters, improvements were made to the filter material microstructures that were coupled with new catalyst formulations and novel coating processes that had synergistic effects to give enhanced overall performance.

It has been reported that particulate emissions from diesel vehicles could be associated with damaging human health, global warming and a reduction in air quality. These particles cover a very large size range, typically 3 to 10 000 nm. Filters in the vehicle exhaust systems can substantially reduce particulate emissions but until very recently it was not possible to directly characterise actual on-road emissions from a vehicle. This paper presents the first study of the effect of filter systems on the particulate emissions of a heavy-duty diesel vehicle during real-world driving. The presence of sulfur in the fuel and in the engine lubricant can lead to significant emissions of sulfate particles < 30 nm in size (nanoparticles).

Emissions from (and cost of) three-way catalysts can minimised by targeted application of PGM along the catalyst's length rather than the conventional homogeneous distribution. Experiments are described demonstrating pollutant conversion as a function of catalyst length during the European MVEG-B cycle. It is shown that most pollutant conversion occurs on the front portion, and that therefore the most effective catalysts have the majority of the PGM content there. Further analysis of the three legislated pollutants CO, HC and NOx leads to insights about the optimum distribution of Pt, Pd and Rh within the catalyst. In advantageous circumstances bi or trimetallic systems can be partially replaced with Rh-only systems with significant cost and backpressure benefits. Further experiments comparing zoned catalysts with current catalysts whose PGM is homogeneously distributed are described, demonstrating additional performance benefits.

Recently, significantly more demanding emissions standards for the Mercosur region were proposed, and the intention is that these will be introduced in 2004 and 2008. This paper describes the development of new high performance three-way catalyst formulations for conventional gasoline/gasohol fueled engines that enables them to meet these stringent standards without increasing the content of platinum group metals above the levels currently employed. The performance benefits of these advanced platinum and palladium-based catalysts are demonstrated on both engine bench and vehicles.

Three-way catalysts based on the use of palladium have proved highly effective at meeting the most stringent emissions legislation around the world. This has led to a rapid increase in the amount of palladium used in autocatalyst applications which has contributed to an increase in the palladium price. This has prompted a renewed interest in the use of platinum in advanced three-way catalyst (TWC) formulations. This paper compares the performance of advanced platinum-rhodium and palladium-rhodium technology on an engine test-bed. This showed the new platinum-rhodium catalyst to have equal or better performance at similar precious metal cost. Tests on selected vehicles confirmed future emissions standards can be achieved using the platinum-based catalysts.

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 control of emissions from mobile sources continues to play an important part in air quality improvement. Future reductions in vehicle emissions are proposed or legislated in many countries throughout the world. The most stringent of these standards under discussion are those in the Californian LEV-II proposal, a part of which is the SULEV standard which requires a large reduction in hydrocarbon emissions, together with a significant decrease in NOx, over those legislated for ULEV. This requires the engine and aftertreatment system to deliver both a substantial reduction in the emissions of hydrocarbon during engine warm-up and increased NOx conversion during high speed operation, compared to previous ULEV systems. In this paper we outline three different catalyst systems which show the potential to provide reduction in vehicle emissions below the currently legislated ULEV and European Stage IV standards.

Exhaust gas flow maldistribution can strongly affect the performance of catalytic converters. As part of an on-going programme concerned with optimising converter designs, flow maldistribution within catalyst monoliths resulting from the use of different shaped inlet cones was investigated. Computational fluid dynamics (CFD) techniques were used to predict gas velocities within the catalyst, and reaction of low levels of hydrogen sulfide in the gas was used to visualise the velocity profile on monoliths coated with a lead acetate indicator. This was done both in laboratory-scale experiments at room temperature with low flow-rates, and in a vehicle exhaust system under reduced temperature conditions. Flow patterns were produced for an underfloor catalyst system under real driving conditions with this unobtrusive chemical technique.

In order to meet future emission standards for gasoline vehicles, catalyst designers have developed thermally durable three-way catalysts with enhanced activity. The most effective catalysts for achieving the required hydrocarbon conversion were those containing high levels of palladium. This has led to increased levels of palladium being used. Recent palladium price fluctuations have created interest in the possibility of using advanced platinum-based technologies. The performance of a new platinum-rhodium three-way catalyst (TWC) was compared with an advanced palladium-rhodium catalyst on an engine test-bed. The results showed the new platinum-rhodium catalyst gave equivalent, or better, performance at similar total precious metal cost. The performance on selected vehicles confirmed future emissions standards can be achieved with platinum-based catalysts.

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.