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The surface electronic structure, the acid-base properties, the component adsorption and the catalytic activity of gamma alumina (CK-300, Ketjen) modified with surface sodium as a donor-type or iron as an acceptor-type additive have been investigated. Alumina was loaded with 0.1 and 1 wt.% Na and Fe. The catalytic 0/!3 exchange of CO, and CS, to form COS was applied as a model reaction, for which the kinetic parameters have also been determined. In the case of unloaded alumina and samples loaded with 0.1 wt.% Na and 0.1 or 1.0% Fe no characteristic differences in the shape and position of the 0 1s and A1 2p lines were observed. However, 1.0 wt.% Na loading resulted in a broadening of the 0 1s and A1 2p lines towards lower binding energies. Sodium, even in 1% monolayer coverage, and other donor-type surface species, e.g. pre-adsorbed NH, or pyridine, exhibited a readily detectable promoter effect which could be characterized by increased surface basicity, increased CO, and CS, adsorption and better catalytic performance. In contrast, on catalysts loaded with Fe an increase in surface acidic sites, a loss of basic sites, decreased component adsorption and lower catalytic activity were observed.