Search Results

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.

By characterizing current three-way catalysts (TWCs) after thermal aging, it was possible to use the information obtained to develop a new generation of more thermally durable TWCs. To assess their performance, a dynamic dynamometer was used to age these new TWC formulations (Pt/Rh and Pd/Rh) at a series of different maximum catalyst operating temperature limits (960, 1010 and 1050°C) using a proprietary transient aging cycle. Each catalyst was evaluated periodically throughout the aging on a dynamic dynamometer to assess its emission performance and aging characteristics. After a representative aging time, both the Pt/Rh and the Pd/Rh formulations were capable of meeting European Stage IV emission standards on a production powertrain after prolonged 1050°C aging. The thermal resistance of the new Pt/Rh and Pd/Rh TWCs is significantly better than that of previous technologies.

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 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.

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.