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.