Spatially resolving LNT desulfation: re-adsorption induced by oxygen storage materials

Abstract

Spatially resolved gas concentration measurements were obtained along a commercial LNT sample, containing both NOx storage and oxygen storage components, during exposure to different levels of sulfur and under mild desulfation conditions. For a partially sulfated sample, with sulfur mainly deposited toward the catalyst inlet, during the desulfation some of the sulfur species released from the front were re-adsorbed along the back part of the catalyst, leading to redistribution of the sulfur species. For the fully sulfated sample, no re-adsorption occurred. Interestingly, for a partially sulfated model sample, Pt/BaO/Al2O3, no re-adsorption was observed. Based on the data obtained from the model and commercial samples, the ceria-based oxygen storage (OS) material plays a crucial role in this sulfur re-adsorption. The OS material's main function in this process is to provide oxygen for the oxidation of the released sulfur species from the front, so that they re-adsorb at the catalyst back. Besides this sulfur redistribution, these OS materials also influence the desulfation products. More H2S, relative to SO2, is released from the OS-containing sample since S ultimately spent more time within the catalyst via re-adsorption and extra reductant consumption by the OS materials. In addition, NOx re-adsorption during regeneration was also observed, leading to a decreased NOx release at the transient from the lean to rich phases. However, the extent of NOx re-adsorption was significantly less relative to sulfur re-adsorption under the test conditions used.