(111a) Keynote Speaker Abstract: Twin Flame Spray Pyrolysis Production of Pt/K/Al2O3 NOx Storage-Reduction Catalysts

Authors: 
Büchel, R., ETH Zurich
Pratsinis, S. E., Swiss Federal Institute of Technology, Particle Technology Laboratory, ETH Zurich
Baiker, A., ETH Zurich


New catalysts for NOx removal are development to meet upcoming stricter emission limits. To reduce NOx under oxygen rich conditions is a major challenge as encountered in lean burn and direct injection engines [1]. NOx storage-reduction (NSR) catalyst can trap exhaust NOx under fuel lean conditions on alkali- or alkaline earth metals in the form of metal-nitrates [2] whereby K and Ba are reported to be the best [3]. The NOx trap is regenerated during a short fuel rich period, where the metal-nitrates are decomposed and the released NOx are reduced to nitrogen [4]. Potassium and barium have been studied extensively for their NOx storage and regeneration behavior whereby K showed higher performance especially at elevated temperatures [5]. Furthermore K2CO3 is less toxic and cheaper than BaCO3. The main drawback of K is its low resistance to sulfur poisoning, whereby regeneration is possible but only above 700°C [6]. Although NSR catalysts are typically used at high temperatures (>350°C), their performance below 350°C is also important [7].

Here, we prepared Pt/K/Al2O3 catalysts using a twin flame spray pyrolysis (FSP) setup [8] allowing to separate synthesis of the support and storage components of the NSR catalyst [9]. This setup also allows controlling the location of Pt-clusters on the support or the storage sites of the NSR catalysts [10]. Raman investigations showed amorphous K2CO3 to bepresent, exhibiting a higher NOx conversion compared to Ba at high as well as low temperatures. The K concentration is a crucial factor for the steady-state NOx conversion efficiency of a given fuel lean/rich cycle length. An advantage of the K based catalysts was that during the switch from fuel lean to fuel rich the typical undesired overshooting of the NOx was decreased for higher temperatures. The superior performance was attributed to good K distribution in the sample as evidenced by STEM combined with EDX analysis. Preferential Pt deposition on K increased the catalyst efficiency, especially during the reduction phase. In contrast to flame made BaCO3 which transforms from orthorhombic to monoclinic structure, amorphous K2CO3 showed no measurable crystal change and stayed stable even during TGA measurements up to 1000°C.

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