Nature of Reverse Water–Gas Shift Reactions at Metal–Oxide Interfaces Uncovered via Interpretable Machine Learning

Oxide-supported metal clusters are central to the reverse water-gas shift (RWGS) reaction, which converts CO₂ to CO; however, the optimal interfacial properties governing activity remain unresolved. Although the oxygen vacancy formation energy (<i>E</i>_V) is known to influence CO₂ activation, its quantitative role and ideal value for catalysis have not been defined owing to the complexity of metal-oxide combinations and reaction pathways. Here, we integrate first-principles microkinetic modeling with interpretable machine learning across nine transition metal clusters on eight oxide supports to identify two key descriptors─<i>E</i>_OV of the support and the atomic radius (<i>r</i>) of the metal cluster─that together control the RWGS reactivity. We reveal a volcano-type relationship between the turnover frequency (TOF) and <i>E</i>_V, with optimal activity emerging at moderate vacancy formation energies (∼3.4 eV). A high <i>E</i>_V suppresses vacancy formation, whereas a low <i>E</i>_V limits CO₂ activation. Additionally, larger metal radii systematically lower the barrier for lattice oxygen reduction, stabilizing the transition state and promoting vacancy regeneration. The reaction mechanism shifts from carboxylate-mediated to direct CO₂ dissociation as <i>E</i>_V increases. Our framework captures experimental trends across reported catalysts and provides a physically grounded, predictive strategy for designing efficient RWGS catalysts by engineering metal-oxide interfaces.