Although the reduction of iron oxides has been widely studied using bulk characterization techniques, direct observations of surface chemical states under reaction conditions remain limited. Here, the reduction behavior of iron oxides in a CO/H2 atmosphere is investigated using ambient-pressure X-ray photoelectron spectroscopy (APXPS) combined with ex situ microstructural characterization. APXPS reveals that the outermost surface remains dominated by a FeO layer under reducing conditions, while complementary microscopy shows the formation of metallic Fe beneath the surface together with localized Fe3C. Diffraction measurements further indicate that oxide phases dominate the bulk. Together, these results reveal a chemically layered structure during iron oxide reduction and provide new insight into the surface chemistry and reaction pathways of metallurgical reduction processes.
}}, author = {{Wang, Yuzhao and Ghosalya, Manoj Kumar and Azadi, Saeid Khesali and Soodmand, Ahmadreza Mohammadian and Chuproski, Rafael Fillus and Kokkonen, Esko and Klyushin, Alexander and Heidari, Aidin and Huttula, Marko and Fabritius, Timo and Urpelainen, Samuli}}, issn = {{1359-6462}}, keywords = {{Apxps; Carburization; Chemical layering; Iron oxide reduction}}, language = {{eng}}, month = {{12}}, publisher = {{Elsevier}}, series = {{Scripta Materialia}}, title = {{Chemical layering during CO/H2 reduction of iron oxides revealed by APXPS and multiscale characterization}}, url = {{http://dx.doi.org/10.1016/j.scriptamat.2026.117530}}, doi = {{10.1016/j.scriptamat.2026.117530}}, volume = {{285}}, year = {{2026}}, }