Abstract
AbstractIron 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 () 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.
Highlights
Stabilizing ever smaller metallic clusters on inexpensive metal oxide supports has been a longstanding goal of catalysis research
Experimental Results First, we investigated the stability of small amounts of Rh on α-Fe2O3(11̅02)-(1 × 1) by depositing 0.025 ML Rh on the freshly prepared surface at room temperature
The peak contains a single component at 309.3 eV, which can be assigned to an oxidized Rh species. This binding energy is significantly higher than the ≈308.6 eV that were previously reported for bulk Rh2O3,[28, 31, 32] and is closer to that reported for RhO2.[31]. In scanning tunnelling microscopy (STM), this development corresponds to a disappearance of the clusters, and single bright features are instead observed at negative sample bias [Figure 1(b)]
Summary
Stabilizing ever smaller metallic clusters on inexpensive metal oxide supports has been a longstanding goal of catalysis research. -called “single-atom” catalysts (SACs) represent the ultimate limit of this endeavour, but stabilizing single atoms against agglomeration under reaction conditions is challenging.[1,2,3,4,5,6,7] To be stable, the metal atoms must form chemical bonds with the support, which affects their electronic structure and catalytic properties. To accurately model such a system requires the atomic-scale structure of the active site to be known. These observations imply a strong driving force for Rh incorporation into the immediate subsurface of hematite, indicating a potential route for redispersion of sintered particles
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