SmMn2O5 catalysts modified with silver for soot oxidation: Dispersion of silver and distortion of mullite

The mullite SmMn2O5 (SMO) was modified with silver for soot oxidation by two methods, i.e. sol-gel (Ag/SMO-sg) and impregnation (Ag/SMO-im). The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectrometry (ICP-AES), H-2-O-2 titration, H-2 temperature-programmed reduction (H-2-TPR), CO temperature-programmed reduction (CO-TPR), soot temperature-programmed reduction (soot-TPR), O-2 temperature-programmed desorption (O-2-TPD), cycled H-2 temperature-programmed reduction (cycled H-2-TPR), NO temperature-programmed oxidation (NO-TPO) and soot temperature-programmed oxidation (soot-TPO). Metallic silver nanoparticles were observed in the mullite matrix for both the catalysts. For Ag/SMO-sg, the possible incorporation of silver into the mullite crystal cell and strong electronic interaction between the highly dispersed metal and the support increase the Mn4+/Mn3+ ratio and create more structural defects in the mullite, resulting in boosted NO oxidation and thereby NO2-assisted soot combustion. The introduction of Ag can promote the generation/regeneration of active oxygen, which accelerates the ignition of soot in O-2 at low temperatures. Therefore, the sol-gel-synthesized Ag/SmMn2O5 is highly promising for application in diesel particulate filters.