Characterization of potassium-promoted iron–manganese catalysts by insitu diffuse reflectance FTIR using NO, CO and CO+H2 as probes Original Research Article

Insitu diffuse reflectance FTIR spectroscopy coupled with adsorption of probe molecules of NO, CO and CO+H2 (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 H2, 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 Fe0. 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 fine metallic iron clusters. At an increased potassium loading, the formed Fe0 species is coated by potassium, so the structural information obtained from infrared measurements reflects only the Fe0 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+H2 demonstrates that the formed metallic iron particles are of moderate size, which may be covered by potassium species.