Regenerable ceria-based SOx traps for sulfur removal in lean exhausts

Bare and Pt-containing CeO2, Al2O3:MgO mixed oxide and Al2O3 have been investigated as potential regenerable sulfur oxides (SOx) traps. The samples were evaluated by lean SOx adsorption and temperature programmed desorption using synthetic gas compositions. In addition, combined DRIFT spectroscopy and mass spectrometry were employed to obtain mechanistic information on the adsorption of SOx. The results suggest Pt/CeO2 as promising SOx trap material owing to a high storage capacity at 250 °C in combination with efficient release above 600 °C. The presence of Pt is generally found to enhance the lean SOx storage capacity at 250 °C for CeO2-based samples. Lean SO2 adsorption on CeO2 is found to proceed via the formation of surface and bulk sulfates, where the latter is formed more rapidly for the Pt-containing CeO2 sample. Ceria samples pre-exposed to high amounts of SO2 at 250 and 400 °C show lower SOx storage capacity and higher SOx release as compared to fresh samples. This indicates that under the conditions used in this study, a part of the storage sites on CeO2 are non-regenerable.