CO oxidation by Pt₂/Fe₃O₄: Metastable dimer and support configurations facilitate lattice oxygen extraction

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/Fe₃O₄(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 CO₂. Pt₂ dimers produce one CO₂ molecule before falling apart into two adatoms, releasing the second CO. O_lattice extraction only becomes facile when both the Pt-dimer and the Fe₃O₄ support can access metastable configurations, suggesting that substantial, concerted rearrangements of both cluster and support must be considered for reactions occurring at elevated temperature.