Insitu diffuse reflectance FTIR spectroscopy coupled with adsorption of probe molecules of NO, CO and CO + H-2 (syngas) was used to investigate the surface adsorption properties of the iron-manganese samples with an Fe/Mn molar ratio of 1:6 loaded with different contents of potassium. It was found that on the oxidized sample without addition of potassium, the Fe2+ species is dominant on the surface. After reduction in H-2, iron species segregates to the surface and metallic iron particles of moderate size are formed. With the addition and increase in loading of potassium in the sample, Fe2+ is converted to some extent to Fe2+(-x) or Fe-0. At the potassium loading of 0.1 wt.%, the potassium species tightly interacts with the surface iron species and promotes its reduction to form the line metallic iron clusters. At an increased potassium loading, the formed Fe-0 species is coated by potassium, so the structural information obtained from infrared measurements reflects only the Fe-0 sites that are not covered by potassium. However, the appearance of different linear and bridged CO adsorption species revealed by the spectra recorded from the: thermal desorption of the adsorbed CO or CO+H-2 demonstrates that the formed metallic iron particles are of moderate size, which may be covered by potassium species.