Surface Reduction State Determines Stabilization and Incorporation of Rh on {\alpha}-Fe2O3(1-102)

TL;DR

This study investigates how the surface reduction state of { extalpha}-Fe2O3(1-102) influences Rh atom stabilization and incorporation, revealing that annealing and oxidation conditions significantly affect Rh behavior and support interaction.

Contribution

It provides new insights into Rh atom stabilization and incorporation mechanisms on reduced and oxidized hematite surfaces using combined experimental and theoretical approaches.

Findings

Rh atoms form clusters at room temperature on both surface terminations.

Above 400°C, Rh atoms incorporate into the lattice as isolated atoms.

Under mildly oxidizing conditions, Rh clusters dissolve into the surface.

Abstract

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, we study Rh adsorption and incorporation on the (1-102) surface of hematite ({\alpha}-Fe2O3), which switches from a stoichiometric (1x1) termination to a reduced (2x1) 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 {\deg}C. Under mildly oxidizing conditions, the incorporation process is so strongly favoured that even large Rh clusters containing hundreds of atoms dissolve into the surface. Based on a combination of low energy ion scattering and scanning tunnelling microscopy data, as well as density functional theory, we conclude that the Rh atoms are stabilized in the immediate subsurface, rather than the surface layer.