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

The mullite SmMn 2 O 5 (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 Mn 4+ /Mn 3+ ratio and create more structural defects in the mullite, resulting in boosted NO oxidation and thereby NO 2 -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/SmMn 2 O 5 is highly promising for application in diesel particulate filters.