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

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. (C) 2014 Elsevier B.V. All rights reserved.