The results reflect a highly dynamic catalytic converter surface that reacts extremely sensitively to external impacts, such as exhaust gas composition.

a) Dynamic nature of Pt on ceria is exploited to adjust noble metal dispersion: 1.) the noble metal is finely dispersed on CeO2 during oxidative treatment by exploiting metal support interaction with ceria. 2.) formation of slightly larger noble metal particles is initiated by application of controlled reducing steps (e.g. pulses) at a low temperature (< 400 °C). b) Redispersion step is not applicable at moderate temperatures for weakly interacting supports like Al2O3. Gänzler et al. Click to enlarge.

We can adjust the size and state of the noble metal nanoparticles on the surface of the catalytic converter. The methods enable us to do this under relevant and even real operation conditions and, hence, to directly adjust the catalytic activity of materials.

—Andreas Gänzler, KIT Institute for Chemical Technology and Polymer Chemistry (ITCP) and lead author

In their study, the researchers demonstrated how sensitively the state of platinum reacts to the composition and the temperature of the exhaust gas. Engine operation already is modified specifically in current exhaust gas aftertreatment systems to adjust the composition of the exhaust gas for the regeneration of particulate filters or NO_x storage catalytic converters. The study reveals that it is also possible to optimally set the active platinum component in order to enhance activity of the catalytic converter and reduce the consumption of noble metal.

The researchers used environmental transmission electron microscopy (ETEM) to visualize structural modifications on the atomic level of the material. X-ray absorption spectroscopy at the SOLEIL synchrotron in the French St. Aubin and at the KARA Karlsruhe Research Accelerator of KIT was applied to study the processes under realistic exhaust gas conditions.

The findings show that catalytic activity of diesel oxidation catalytic converters can be enhanced at low temperature. From their observations, the scientists derived a promising basic concept specifically to adjust the size and structure of platinum particles as a function of the catalytic activity required during operation. T

The concept can be used significantly to improve catalytic performance after the cold start of combustion engines and when driving in urban traffic.

The structure of the noble metal nanoparticles can be influenced by short-term modifications of the engine operation mode, for instance.

—Andreas Gänzler

Based on the findings, current and future new types of catalytic converters can be improved and their economic efficiency can be increased, as the noble metal concentration can be reduced by up to 50%.

The study was carried out in the course of the project “ORCA – Oxidation/Reduction Catalytic Converter for Diesel Vehicles of the Next Generation” that is part of the Deufrako German-French research collaboration. The project is funded with €960,000 (US$1.1 million) by the Federal Ministry for Economic Affairs and Energy. Apart from KIT, the Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON), TU Darmstadt, the Solvay company, and Umicore AG & Co. KG, a materials technology and recycling company in Hanau, took part in the project.

Resources

• Andreas M. Gänzler, Maria Casapu, Philippe Vernoux, Stéphane Loridant, Francisco J. Cadete Santos Aires, Thierry Epicier, Benjamin Betz, Rüdiger Hoyer, and Jan-Dierk Grunwaldt (2017) “Tuning the Structure of Platinum Particles on Ceria In Situ for Enhancing the Catalytic Performance of Exhaust Gas Catalysts.” Angew. Chem. Int. Ed. 56, 13078 doi: 10.1002/anie.201707842