Boosting the catalytic activity of magnetite in soot oxidation by surface alkali promotion

•Presence and type of alkali metal is of high importance for Fe3O4 surface promotion.•The highest effect of each dopant corresponds to different surface coverage.•Minimum work function of the catalyst results in the highest catalytic activity.•Temperature window of the soot oxidation reaction is shifted down by 350°C.

The effect of alkali promotion of a Fe3O4 catalyst in soot combustion was systematically investigated for a series of alkali elements (Li, Na, K and Cs) at various surface coverages. The correlation between catalyst performance and work function lowering was established and discussed in terms of the electron donor character of the alkali promotion. This effect was found to follow the sequence of the increasing ionic radii of the alkali promoters Li < Na < K < Cs. For each alkali promoter, the highest activity corresponds to a different optimal surface coverage.