Catalytic converters are an essential component of almost every modern car on the road that uses an internal combustion engine, but the job they do purifying exhaust gases requires the use of increasingly scarce and costly precious metals. Intensive R&D by Toyota has produced a new, world-first1 catalyst design that reduces the precious metal content by as much as 20 per cent.
The new unit, which is also smaller in volume by 20 per cent, is ready for mass production and will be first introduced on the new Lexus LC 500h hybrid luxury coupe later this year.
The design features the world’s first integrally moulded Flow Adjustable Design Cell (FLAD®2) substrate. Its key feature is a different cross-section for the cells in the inner and outer parts of the catalyst.
Toyota focused on defining the best substrate shape and length, as well as modifying the thickness of the cell wall and the cross-sectional area. Other R&D work investigated the selective wash-coating of precious metals and other materials used in the catalyst and a change in substrate cell density in line with the exhaust gas flow rate.
The new FLAD® substrate has been developed by Toyota and the Denso Corporation to improve the uniformity of exhaust gas flow. Simulations and prototypes were used in a series of validations, leading to the successful optimisation of factors such as the ratios of the cross-sectional areas of cells in the inner and outer portions of the catalyst and their corresponding densities. This development has allowed for the use of approximately 20 per cent less precious metal in a more compact catalyst (approximately 20 per cent smaller in volume), while maintaining the same exhaust gas purification performance as a conventional unit. Innovative design and manufacturing technologies have enabled this design to be put into mass production.
A uniform exhaust gas flow within the catalysts installed in exhaust systems enables the wash-coated precious metals and other catalytic materials to purify the gas effectively. However, the use of conventional substrates with a uniform cell cross-sectional area results in an unbalanced flow, as gas will move faster and in a higher volume through the inner portion compared to the outer portion. As a result, a greater amount of catalytic precious metal is needed in the inner portion, where flow rate is higher, in order to maintain the purification performance.
Current catalytic material wash-coating technologies require all cell walls to be coated equally during the wash-coating process, which means the same amount of precious metal is used in all areas, both where the gas flow rate is higher and lower.
Toyota will continue to work with companies within its group and related business partners to further develop catalyst technologies that will achieve cleaner exhaust gas while using less precious metal.
1 As of January 2017, according to Toyota research
2 FLAD (Flow Adjustable Designed Cell) is a registered trademark of Denso Corporation.