Metal–Support Interaction in In2O3-Based Catalysts of CO2 Hydrogenation Studied Using “Inverse” In2O3(111)/Ru(0001) Model Systems

Indium oxide (In₂O₃) has recently received considerable attention in the catalysis community due to its unexpectedly high selectivity in the hydrogenation of CO₂ to methanol. Metal deposition onto In₂O₃ substantially promotes the activity, while the selectivity remains close to that of bare In₂O₃, independent of the metal used. To get insight into the metal/In₂O₃ interaction and the role of the metal/oxide interface in the CO₂ hydrogenation reaction, we carried out a near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) study of “inverse” model catalysts prepared by In(III) oxide deposition onto a Ru(0001) substrate. Bulk-like In₂O₃(111) islands grow on the Ru(0001) surface at the onset of the deposition, and a continuous film is obtained above 5–7 nm of the nominal thickness. NAP-XPS measurements of the In₂O₃(111) films of various film thickness revealed the formation of metallic In(0) species at 200–280 °C in pure H₂ and CO₂ + H₂ atmospheres if In₂O₃ partially covers the Ru surface but not on the continuous films. Moreover, these species formed in the H₂ containing ambient are altered considerably in the post-reaction samples, highlighting the necessity of operando studies on In₂O₃-based catalysts. Obviously, the In(0) formation is assisted by facile H₂ dissociation on the Ru surface, with H adatoms reacting at the interface to In₂O₃. XPS results obtained for reference systems prepared by direct In deposition showed that metallic In(0) formed in the H₂ atmosphere remains at the In₂O₃/Ru interface and does not migrate onto Ru to form a surface alloy.