(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 NOx storage-reduction (NSR) catalyst can be used. The exhaust NOx 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 . 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 . While Pt located on Ba promoted the Ba-nitrate regeneration  the support effect can change the catalytic behavior significantly .
Mono- and bimetallic Rh and Pt based NOx 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.
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