Iron catalysts with and without a potassium promoter have been studied in a combined temperature-programmed reaction and flow microreactor system connected to a mass spectrometer. This arrangement has the advantage that sample characterization through temperature-programmed methods can be carried out alternating with measurements of synthesis reaction rates. The desorption studies demonstrate a significant shift of the N2 desorption peak to lower temperatures with the addition of K to the catalyst. This change suggests a destabilization of dissociated nitrogen. The N2 adsorption results are generally in good agreement with earlier studies of singly promoted catalysts. Thus the rate was found to be slow and activated. The addition of K has little effect on the temperature-programmed adsorption (TPA) curves, while for multiply promoted catalysts there is a significant shift of the main adsorption dip to lower temperatures. However, the adsorption was still activated even for this type of catalyst.