(69d) Sulfur Poisoning of NOx Storage Reduction Catalysts: Influence the Noble Metal Position of Mono- and Bimetallic Rh and Pt

To limit emission from automobiles NO_x storage-reduction (NSR) catalyst can be used. The exhaust NO_x is trapped first under oxygen rich conditions on an alkali or alkaline-earth metal (like K or Ba) in the form of metal-nitrates and reduced during fuel rich conditions [1]. Catalyst deterioration at high temperatures and sulfur poisoning are currently limiting its application. Previously preferential located Pt on Al₂O₃ or BaCO₃ on Pt/Ba/Al₂O₃ NSR catalysts was made with a 2 nozzle flame spray pyrolysis (FSP) unit [2]. While Pt located on Ba promoted the Ba-nitrate regeneration [3] the support effect can change the catalytic behavior significantly [4].

Mono- and bimetallic Rh and Pt based NO_x storage-reduction (NSR) catalysts, where the noble metals were deposited on the Al₂O₃ support or BaCO₃ storage component, have been prepared using a 2-nozzle flame spray pyrolysis setup. The catalysts were characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy, X-ray diffraction, and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy. The NSR performance of the catalysts was investigated by fuel lean/rich cycling in the absence and presence of SO₂ (25 ppm) as well as after H₂ desulfation at 750 °C. The performance increased when Rh was located on BaCO₃ enabling good catalyst regeneration during the fuel rich phase. Best performance was observed for bimetallic catalysts where the noble metals were separated, with Pt on Al₂O₃ and Rh on BaCO₃. The Rh-containing catalysts showed much higher tolerance to SO₂ during fuel rich conditions and lost only little activity during thermal aging at 750 °C.

References

[1]        S. Roy, A. Baiker, Chem. Rev. 109 (2009) 4054-4091.

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

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

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