SO2 promoted alkali metal doped Ag/Al2O3 catalysts for CH4-SCR of NOx

Abstract A study of the lean NO x reduction activity in the presence of SO 2 and water over alkali promoted Ag/Al 2 O 3 catalysts has been done using methane as a reductant. The alkali doped materials are synthesized by the co-impregnation method. Their promotional behavior, existence of several silver species and improved adsorption properties have been thoroughly investigated by various techniques: XRD, XANES, TEM, UV–Vis DRS, SO 2 TPD and NO TPD. The evaluated samples exhibited high surface area around 220 m 2  g −1 . TEM results demonstrated the presence of highly dispersed nano sized silver particles on surface, where the addition of alkali metals slightly enhanced the crystallization of silver. Moreover, standard XRD profiles of fresh and used samples indicate the high durability and mechanical strength of catalysts. These findings are in line with the time-on-stream studies. The XANES results revealed that the edge spectra of prepared materials are similar to that of the reference Ag 2 SO 4. From XANES and UV–Vis DRS, the presence of crystalline Ag 0 and Ag + species were identified. Poor activity of Na promoted sample is attributed to absence of suitable amount of ionic silver compounds. However, the synthesized alkali doped materials showed the promotional deNO x conversions in the presence of SO 2 and H 2 O stream. Among the investigated samples K–Ag/Al 2 O 3 and Cs–Ag/Al 2 O 3 exhibited higher NO x conversions and thermal stability. The higher SCR of NO x was explained by the NO adsorption properties identified from the NO TPD studies.