Enhancement of Activity and Self-reactivation of NSR-catalysts by Temporary Formation of BaPtO 3 -perovskite
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Enhancement of Activity and Self-reactivation of NSR-catalysts by Temporary Formation of BaPtO3-perovskite Maria Casapu Æ Jan-Dierk Grunwaldt Æ Marek Maciejewski Æ Alfons Baiker Æ Ru¨diger Hoyer Æ Meike Wittrock Æ Stephan Eckhoff
Received: 28 September 2007 / Accepted: 27 October 2007 / Published online: 15 November 2007 Ó Springer Science+Business Media, LLC 2007
Abstract Calcination of a Pt/Ba/CeO2 catalyst at 700 °C and subsequent reduction in hydrogen, carbon monoxide or propene at 350–550 °C resulted in a considerable improvement of its NOx storage-reduction (NSR) properties compared to those of a freshly prepared Pt/Ba/CeO2 catalyst. This behavior is traced back to the temporary formation of BaPtO3 perovskite which leads after reduction to well-distributed Pt particles in intimate contact with the barium-containing phases. The oxidation and reduction of platinum is reversible which can be exploited for the design of ‘‘self-regenerating’’ NSR-catalysts under lean ([600 °C) and rich ([400 °C) reaction conditions. The formation of the BaPtO3-perovskite may not only be interesting for NSR-catalysis, but generally for Pt-based catalysts where a high dispersion of Pt is important. Keywords NOx storage-reduction catalyst NOx removal Perovskite Self-regeneration Aging X-ray absorption spectroscopy Pulse thermal analysis
M. Casapu J.-D. Grunwaldt (&) M. Maciejewski A. Baiker (&) Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, ETH Zurich, Ho¨nggerberg, Zurich 8093, Switzerland e-mail: [email protected] A. Baiker e-mail: [email protected] R. Hoyer M. Wittrock S. Eckhoff Umicore AG & Co. KG, Rodenbacher Chaussee 4, 63403 Hanau-Wolfgang, Germany
1 Introduction One of the challenges in noble metal based catalysis is to achieve a high dispersion of the noble metals not only after preparation but also after many operating cycles [1]. This is particularly important in exhaust gas catalysis where one of the most stringent problems is the deterioration of the catalytic activity due to sintering of metal particles at high temperatures [2–4]. Usually, supports with high surface area and high thermal stability are applied, but this cannot suppress the growth of the precious metal particles during operation [1]. Moreover, much effort has to be done to finely disperse the noble metal in freshly prepared catalysts. An alternative promising strategy is to form noble metal perovskites [5]. The periodic incorporation of the metal into the perovskite lattice under oxidizing conditions and migration out of the perovskite upon reducing conditions is characteristic for a self-regeneration behavior, as already reported in three way catalysis [6, 7]. Most of the studies have been reported on Pd catalysts, whereas only a few investigations considered the use of this strategy also for Rh- or Pt-containing catalysts [8, 9]. Moreover, this concept has not been applied yet on NOx storage-reduction (NSR) catalysts, including the preparation of highly dispersed Pt particles.
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