Surface Reduction State Determines Stabilization and Incorporation of Rh on α‐Fe2O3(11¯02). Issue 8 (4th February 2021) - Kraushofer, Florian
Abstract: Iron oxides (FeO x ) are among the most common support materials utilized in single atom catalysis. The support is nominally Fe2 O3, but strongly reductive treatments are usually applied to activate the as‐synthesized catalyst prior to use. Here, Rh adsorption and incorporation on the ( 1 1 ¯ 02 ) surface of hematite (α‐Fe2 O3 ) 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. Abstract : Adsorption of Rh is investigated on stoichiometric and reduced terminations of α‐Fe2 O3 ( 1 1 ¯ 02 ). Neither surface stabilizes single Rh atoms at room temperature, but Rh incorporates as single atoms into the immediate subsurface at slightly oxidizing conditions. Indeed, this process is so favorable that even large clusters, consisting of hundreds of rhodium atoms, can be dissolved and re‐dispersed in the surface.