(610e) Preferential Deposition of Noble Metals Pt and Pd in K/Al2O3 NOx Storage-Reduction Catalysts | AIChE

(610e) Preferential Deposition of Noble Metals Pt and Pd in K/Al2O3 NOx Storage-Reduction Catalysts


Pratsinis, S. E. - Presenter, Swiss Federal Institute of Technology, Particle Technology Laboratory, ETH Zurich
Baiker, A. - Presenter, ETH Zürich

To reduce automobile emission, NOx storage-reduction (NSR) catalysts can be used to trap NOx under fuel lean conditions on an alkali or alkaline-earth metal (typically Ba or K) in the form of metal-nitrates [1]. The NOx trap is regenerated under fuel rich conditions by decomposing the nitrates and reducing all NOx to nitrogen [2]. As noble metal, typically Pt is used [3] which is only surpassed by Pd at temperatures below 400 °C [4]. With a two flame spray pyrolysis (FSP) unit [5], Pt/Pd/K/Al2O3-catalysts were prepared with Pd and Pt clusters selectively deposited on the K-component or the alumina support and the effect of the noble metal was analyzed. Both noble metals were selectively deposited [6] on the K-storage component or the Al-support in various combinations to investigate the best location of the noble metal and the most favorable Pt/Pd weight ratio. At low temperatures [7], where NOx reduction is most challenging, the noble metal catalysts activity changes significantly. The catalysts were characterized by XRD, BET, CO chemisorption and their NOx storage-reduction behavior was investigated during fuel lean/rich cycling. At 300 °C all catalysts showed NOx conversion above 90%. Among the monometallic catalysts, Pt showed the best performance at 250 °C when it was deposited on the K component while Pd was most effective when deposited on the alumina constituent. At 250 °C the NOx reduction activity of Pd was low and its presence in some cases even lowered the overall NOx conversion rate in bimetallic systems.


[1] N. Miyoshi, S. Matsumoto, K. Katoh, T. Tanaka, J. Harada, N. Takahashi, K. Yokota, M. Sugiura, K. Kasahara, SAE Technical Paper 950809 (1995)

[2] A. Fritz, V. Pitchon, Appl. Catal. B 13 (1997) 1-25.

[3] M.O. Symalla, A. Drochner, H. Vogel, R. Büchel, S.E. Pratsinis, A. Baiker, Appl. Catal., B 89 (2009) 41-48.

[4] Y. Su, K.S. Kabin, M.P. Harold, M.D. Amiridis, Appl. Catal. B-Environ. 71 (2007) 207-215.

[5] R. Strobel, L. Madler, M. Piacentini, M. Maciejewski, A. Baiker, S.E. Pratsinis, Chem. Mater. 18 (2006) 2532-2537.

[6] R. Büchel, R. Strobel, F. Krumeich, A. Baiker, S.E. Pratsinis, J. Catal. 261 (2009) 201-207.

[7] H.L. Fang, S.C. Huang, R.C. Yu, C.Z. Wan, K. Howden, SAE Tech. Paper 2002-01-2889 (2002)