SnO_2 promoted by alkali metal oxides for soot combustion: The effects of surface oxygen mobility and abundance on the activity

摘要

Graphical abstractDisplay OmittedHighlights•The addition of alkali metal oxides improves soot combustion activity of SnO2.•Alkali metal oxides induce the formation of more abundant surface oxygen species.•The activity of the catalysts is proportional to the surface mobile oxygen amount.•The amount of surface mobile oxygen species is the major factor deciding the activity.•Cs-modified SnO2shows the best activity due to its richest surface oxygen species.AbstractIn this study, SnO2-based catalysts promoted by different alkali metal oxides with a Sn/M (M = Li, Na, K, Cs) molar ratio of 9/1 have been prepared for soot combustion. In comparison with the un-modified SnO2support, the activity of the modified catalysts has been evidently enhanced, following the sequence of CsSn1-9 > KSn1-9 > NaSn1-9 > LiSn1-9 > SnO2. As testified by Raman, H2-TPR, soot-TPR-MS, XPS and O2-TPD results, the incorporation of various alkali metal oxides can induce the formation of more abundant and mobile oxygen species on the surface of the catalysts. Moreover, quantified results have proved that the amount of the surface active oxygen species is nearly proportional to the activity of the catalysts. CsSn1-9, the catalyst promoted by cesium oxide, owns the largest amount of surface mobile oxygen species, thus having the highest activity among all the studied catalysts. It is concluded that the amount of surface active and mobile oxygen species is the major factor determining the activity of the catalysts for soot combustion.