Reversible modulation of metal active site ensembles within doped perovskite oxides to drive switchable catalytic outcomes

<jats:p> Metal active site structure determines catalytic function and in conventionally supported catalysts, is largely set at synthesis inception. In contrast, ordered mixed metal oxide architectures ( <jats:italic toggle="yes">i.e.</jats:italic> perovskites), circumvent this limitation by acting as hosts for catalytically-active metal cations, whose redox-driven mobility between the bulk and the surface can be used to reversibly control active site speciation and consequently, catalytic outcomes. Herein, redox-driven Rh mobility in Rh-doped SrTiO <jats:sub>3</jats:sub> is shown to modulate active Rh speciation between isolated and extended structures along with changes in interfacial structures and oxidation states, leading to switchable catalytic behavior for CO <jats:sub>2</jats:sub> hydrogenation, a structure-sensitive reaction. Through combined <jats:italic toggle="yes">in situ</jats:italic> X-ray absorption spectroscopy, <jats:italic toggle="yes">in situ</jats:italic> infrared spectroscopy, <jats:italic toggle="yes">in situ</jats:italic> electron microscopy, chemical titration measurements, and kinetic experiments, we demonstrate that the controlled transformation of Rh speciation from lattice-coordinated isolated site species to metallic ensembles switches CO <jats:sub>2</jats:sub> hydrogenation product selectivity between CO and CH <jats:sub>4</jats:sub> . Importantly, these distinct catalytic states and their accompanying selectivities are reversible, which has not been demonstrated to date. Through doping-exsolution-reincorporation cycles, the same perovskite can be switched between functionally distinct active site ensemble states, enabling programmable control over product selectivity between CO and CH <jats:sub>4</jats:sub> within a single catalyst platform that was not attainable within supported catalyst references. Overall, this work demonstrates a novel reversibility for metal site speciation in tunable perovskites through controlling cation mobility, enabling distinct catalytic functions within a single catalytic material and opening new opportunities for these promising catalyst platforms to drive fundamentally different chemistries, each with diverse active site demands. </jats:p>