Enhanced sulfur tolerance of ceria-promoted NOx storage reduction (NSR) catalysts: sulfur uptake, thermal regeneration and reduction with H2(g)
SOx uptake, thermal regeneration and the reduction of SOx via H2(g) over ceria-promoted NSR catalysts were investigated. Sulfur poisoning and desulfation pathways of the complex BaO/Pt/CeO2/Al2O3 NSR system was investigated using a systematic approach where the functional sub-components such as Al2O3, CeO2/Al2O3, BaO/Al2O3, BaO/CeO2/Al2O3, and BaO/Pt/Al2O3 were studied in a comparative fashion. Incorporation of ceria significantly increases the S-uptake of Al2O3 and BaO/ Al2O3 under both moderate and extreme S-poisoning conditions. Under moderate S-poisoning conditions, Pt sites seem to be the critical species for SOx oxidation and SOx storage, where BaO/Pt/Al2O3 and BaO/Pt/CeO2/Al2O3 catalysts reveal a comparable extent of sulfation. After extreme S-poisoning due to the deactivation of most of the Pt sites, ceria domains are the main SOx storage sites on the BaO/Pt/CeO2/Al2O3 surface. Thus, under these conditions, BaO/Pt/CeO2/Al2O3 surface stores more sulfur than that of BaO/Pt/Al2O3. BaO/Pt/CeO2/Al2O3 reveals a significantly improved thermal regeneration behavior in vacuum with respect to the conventional BaO/Pt/Al2O3 catalyst. Ceria promotion remarkably enhances the SOx reduction with H2(g).