Environmental Stability of Model Single-Atom Catalysts

Abstract

Single-Atom Catalysis (SAC) may provide unique reactivity and ideal dispersion of the active metal. However, while many examples have been synthesized successfully, there is a fundamental mismatch between most experimental work and the theoretical modelling of these systems. Applied catalysts are based on complex powder supports, and are fabricated and used in environments containing various potential ligands and contaminants. In contrast, theoretical treatment is generally based on density functional theory (DFT) calculations assuming low-index facets on idealized supports, often placing the single catalyst atom in a bulk-continuation site. Single-crystal supports prepared in UHV provide a direct experimental analogue to DFT and a bridge to more complex systems, validating or correcting the sites assumed by theory. 1,2 UHV-based experiments have shown that simple ligands such as CO and H2O, which will be present in most realistic conditions, can both stabilize or destabilize the metal adatoms: If the pristine, UHV-prepared surface already presents a good binding template, as is the case on Fe3O4 (001), added ligands may weaken the catalyst–support interaction, thus inducing mobility and agglomeration.3,4 On the other hand, when ligands bind to both adatoms and 5 support,theycanstabilizethesingle-atomconfigurationandpreventclustering,asisthecasewithwateronα-Fe2O3(1102). Iwillshowhowtheseligand- mediated stabilization and destabilization mechanisms translate to more realistic environments, i.e., liquid and (near-)ambient pressure environments of H2O, O2, and CO. ̅ We have developed two SAC model systems on iron oxides single crystals, the (001) facet of magnetite (Fe3O4) and the (1102) facet of hematite (α-Fe2O3). 1. 2. 3. 4. 5. R. Bliem et al., Science 2014, 346, 1215 F. Kraushofer et al., J. Phys. Chem. C 2018, 122, 1657 G. S. Parkinson et al., Nat. Mater. 2013, 12, 724 R.Bliemetal.,Proc.Natl.Acad.Sci.2016,113,8921 F.Kraushoferetal.,ACSEnergyLett.2022,7,375