Magnesia-supported potassium oxide catalysts for soot combustion: effect of Fe addition on the catalyst activity and stability

This work shows that loading Fe into the K/MgO catalyst for soot combustion can reduce K volatilization due to the formation of potassium-iron oxide compounds. K/MgO and K-Fe/MgO catalysts were prepared by the impregnation of potassium and iron precursors on MgO, and their activity for soot combustion was assessed by thermogravimetric analysis. Catalysts were characterized by atomic absorption spectroscopy, BET surface area, X-ray diffraction and X-ray photoelectron spectroscopy. Fe addition on K/MgO catalyst enhanced its catalytic activity, which is ascribed to a larger K retention into the catalysts either as potassium oxides or as K-Fe-O compounds. The non-stoichiometric potassium oxide (KXOY) is considered as the active phase of this kind of catalysts; it tends to migrate to the surface and to coat the Fe and K-Fe oxides compounds, increasing the surface concentration of active sites for soot combustion. Thus, molecular oxygen from the gas phase is activated over these potassium oxides to generate highly active oxygen species that finally oxidize the carbonaceous matter through an oxygen-transfer mechanism.