Fast-regenerable sulfur dioxide absorbents for lean-burn diesel engine emission control

It is known that sulfur oxides contribute significantly and deleteriously to the overall performance of lean-burn diesel engine after-treatment systems, especially in the case of NOx traps. A silica-supported silver-based, fast regenerable SO2 absorbent has been developed and will be described. Over a temperature range of 300–550 °C, it absorbs SO2 present in a simulated exhaust gas during the lean cycles, and can be fully regenerated by short rich gas cycles at the same temperature. The preferred silica support is fumed silica. The thermal instability of Ag2O under fuel-lean conditions at 230 °C and above makes it possible to rapidly regenerate the sulfur-loaded absorbent during the fuel-rich cycle due to the lack of a requirement to simultaneously reduce Ag2O to Ag. Ag particles can also effectively oxidize SO2 to SO3, facilitating the formation of Ag2SO4 and requiring no additional oxidation catalysts. This absorbent shows great potential to work under the same lean-rich cycling conditions as those imposed on the NOx traps, and thus can protect the downstream particulate filter and the NOx trap from sulfur poisoning.

Figure optionsDownload as PowerPoint slideResearch highlights▶ A Ag-based, fast regenerable SO2 absorbent has been developed. ▶ It absorbs almost all of the SO2 in the simulated diesel engine exhaust gases during the regular fuel lean cycles. ▶ It can be fully regenerated to release sulfur as SO2 under the short fuel rich cycles at the same temperature. ▶ It can be used to protect the lean-burn engine emission after-treatment systems, especially in the case of NOx traps.