Background: Novel ways of increasing the performance of heterogeneous catalysis are always
being sought. Microwave irradiation is one such potential pretreatment method and is expected
to be useful in the modification (for better or worse) of iron-based catalysts since the iron oxide precursors
are good microwave radiation absorbers.
Methods: Iron based Fischer-Tropsch catalysts were subjected to microwave radiation and their catalytic
performance compared with untreated samples. Surface and bulk characterization were carried out in order to try to
explain any changes in catalytic behavior observed.
Results: Increases in activity and changes in selectivity (methane, olefins, growth probability, water gas shift contribution)
have both been observed and the mode of interaction appears to involve potassium mobilization when added as a
promotor, since potassium: silica and potassium: iron surface elemental abundances are changed by the radiative treatment.
The surface properties of the catalysts are modified, as detected by the temperature programmed surface reaction
(TPSR) of adsorbed carbon monoxide with hydrogen. The TPSR profiles seen are sensitive to both the duration and power
level of microwave radiation used.
Conclusion: Microwave radiation can be used to modify the behavior of iron-based catalysts and appears to work by
causing changes in the surface rather hen the bulk properties of the solids. Elemental abundances at the surface change as
does the chemisorption of carbon monoxide and reactivity of the latter with hydrogen. The effects are easily induced and
appear to be long-lived.