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BASF’s new four-way conversion catalyst: TWC plus particulate filter

BASF researchers have further developed the three-way conversion catalyst and optimized its cleaning effect. The new four-way conversion catalyst, FWC, is a technology for vehicles with gasoline engines. The catalyst removes the gaseous pollutants and now also solids such as particulates from the exhaust gas flow.

Compared to the ubiquitous three-way conversion catalyst and the downstream uncoated particulate filter, the new FWC occupies much less space, said Dr. Klaus Harth, responsible for research on automotive catalytic converters at BASF. “The compact four-way conversion catalyst now combines all the important properties in a single component.


The well-known three-way conversion catalyst—in use in North America since 1976 and in Europe since 1986—is now capable of removing considerably more than 95% of the undesired substances from the exhaust gas flow.
This is achieved by the internal structure of the conversion catalysts: exhaust gas catalysts are made of a special ceramic support, the monolith, which contains numerous parallel channels. Depending on their intended use, the channel walls have differently sized pores.
This ceramic support is covered with a washcoat containing metal oxide particles with a very large internal surface. The washcoat contains finely distributed precious metal particles (such as palladium and rhodium in three-way conversion catalysts). These materials are catalytically active and ensure the conversion of CO, noncombusted HC and NOx into water, nitrogen and CO2.

The FWC produces only a slight backpressure to the exhaust gas flow, said Harth. A high backpressure increases the resistance the exhaust gas flow has to overcome before it reaches the exhaust system. If the backpressure is too high, this impairs the performance of the engine and lowers fuel efficiency.

To keep the backpressure as low as possible, BASF experts have developed innovative production and coating technologies. These make it possible, for example, to coat the porous inner walls of the monolith specifically with the catalytically active material.

The porous monolith wall for the catalyst also acts as a filter for the particulates, which are retained by the wall and combusted to carbon dioxide at high temperatures and with the aid of the catalytic coating.

Because most of the particulates are combusted to CO2, the pores of the catalyst do not easily clog—ensuring that the components remain functional. The long-term stability has already been demonstrated in a series of tests: even after more than 160,000 kilometers driven, the four-way conversion catalyst still cleans the exhaust gas effectively achieving stringent emission limits.

The system was introduced in April 2013 and is now in the development and test phase with numerous automotive manufacturers with a view to serial production.


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