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F. Kraushofer, N. Resch, M. Eder, A. Rafsanjani-Abbasi, S. Tobisch, Z. Jakub, C. Franchini, M. Riva, M. Meier, M. Schmid, U. Diebold, G. Parkinson:
"Surface reduction state determines stabilization and incorporation of Rh on α-Fe₂O₃(1 -1 0 2)";
Advanced Materials Interfaces, 8 (2021), 20019081 - 20019088.

Iron oxides (FeOx) are among the most common support materials utilized in
single atom catalysis. The support is nominally Fe2O3, but strongly reductive
treatments are usually applied to activate the as-synthesized catalyst prior to use.
Here, Rh adsorption and incorporation on the (11110022) surface of hematite
(α-Fe2O3) are studied, which switches from a stoichiometric (1 × 1) termination to
a reduced (2 × 1) reconstruction in reducing conditions. Rh atoms form clusters
at room temperature on both surface terminations, but Rh atoms incorporate
into the support lattice as isolated atoms upon annealing above 400 °C. Under
mildly oxidizing conditions, the incorporation process is so strongly favored that
even large Rh clusters containing hundreds of atoms dissolve into the surface.
Based on a combination of low-energy ion scattering (LEIS), X-ray photoelectron
spectroscopy (XPS) and scanning tunneling microscopy (STM) data, as well as
density functional theory (DFT), it is concluded that the Rh atoms are stabilized in
the immediate subsurface, rather than the surface layer.

http://dx.doi.org/10.1002/admi.202001908

https://publik.tuwien.ac.at/files/publik_297561.pdf