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The article discusses research showing the ordered array of subsurface iron vacancies and interstitials underlying the (√2 x √2)R45° surface reconstruction of the iron oxide magnetite Fe3O4(001). Topics include cation vacancy stabilization of the magnetite surface, the role played by oxygen vacancies (VOs), and subsurface cation vacancy (SCV) structure determined with density functional theory-based calculations (DFT+U).

Heterogeneous catalysts based on subnanometer metal clusters often exhibit strongly size-dependent properties, and the addition or removal of a single atom can make all the difference. Identifying the most active species and deciphering the reaction mechanism is extremely difficult, however, because it is often not clear how the catalyst evolves in operando. Here, we use a combination of atomically resolved scanning probe microscopies, spectroscopic techniques, and density functional theory (DFT)-based calculations to study CO oxidation by a model Pt/Fe 3 O 4 (001) "single-atom" catalyst. We demonstrate that (PtCO) 2 dimers, formed dynamically through the agglomeration of mobile Pt-carbonyl species, catalyze a reaction involving the oxide support to form CO 2 . Pt 2 dimers produce one CO 2 molecule before falling apart into two adatoms, releasing the second CO. O lattice extraction only becomes facile when both the Pt-dimer and the Fe 3 O 4 support can access metastable configurations, suggesting that substantial, concerted rearrangements of both cluster and support must be considered for reactions occurring at elevated temperature.

Understanding how the local environment of a "single-atom" catalyst affects stability and reactivity remains a challenge. We present an in-depth study of copper 1 , silver 1 , gold 1 , nickel 1 , palladium 1 , platinum 1 , rhodium 1 , and iridium 1 species on Fe 3 O 4 (001), a model support in which all metals occupy the same twofold-coordinated adsorption site upon deposition at room temperature. Surface science techniques revealed that CO adsorption strength at single metal sites differs from the respective metal surfaces and supported clusters. Charge transfer into the support modifies the d-states of the metal atom and the strength of the metal-CO bond. These effects could strengthen the bond (as for Ag 1 -CO) or weaken it (as for Ni 1 -CO), but CO-induced structural distortions reduce adsorption energies from those expected on the basis of electronic structure alone. The extent of the relaxations depends on the local geometry and could be predicted by analogy to coordination chemistry., (Copyright © 2021, American Association for the Advancement of Science.)