The performance of TWCs today is
astonishing compared with that of catalysts introduced three and a half decades
ago. Activity is high and thermal stability is so good catalyst is now placed
on the exhaust manifold where it heats up rapidly when the engine is started,
and in this hot location less PGM is needed than in a cooler downstream
location 25 . Information about catalyst temperature can be useful to design a
closed-loop control strategy focused on TWC warm up to minimize pollutant
emissions and the fuel consumption during a cold start.
Development of more accurate fuel injectors,
that were able to accurately control the amount of the injected fuel, was the
system able to obtain the necessary high performance.
Thus performance is very high with use of less costly materials
than previously was the case. A drawback of three-way catalytic converters at
the time of their introduction was that a very accurate engine air/fuel control
was necessary to maintain the exhaust mixture at stoichiometry. With the
development of exhaust gas oxygen (EGO) sensors, popularly called ? sensors, it
was possible to develop a control system that keeps the engine air/fuel ratio
Performance is routinely monitored by
on-board diagnostics (OBD) via two oxygen sensors (one upstream and one
downstream of the TWC)via computer
algorithms that periodically change the exhaust oxygen content and thereby determine the level of active oxygen
storage capacity of the catalyst 26 .
Major developments in converter’s
durability, decreased susceptibility to poisoning, thermal stability, etc.
Light-off temperature (the temperature where the conversion reaches 50%) of
converter is constantly decreasing, together with improvements in catalyst’s
oxygen storage capability. As a result a new generation of catalysts has now
been developed with substantially improved thermal stability.
Together with the advances in the converter performance, the last
decade has also witnessed great improvements in the engine electronic control
system. The engine exhaust after treatment system is thus becoming one of the
most advanced collaborations between chemistry and electronics.