In Situ Observations of CO₂ Activation on the PdIn(111) Alloy Surface at Ambient Pressures

The CO₂ activation process has been investigated on the palladium-indium (PdIn) (111) alloy surface using ambient pressure scanning tunneling microscopy (AP-STM) and synchrotron-based X-ray photoelectron spectroscopy (AP-XPS). Pd and In atoms diffuse onto the topmost layer after annealing at 840 K, which adopts intermetallic PdIn alloy geometries in an ultrahigh vacuum. AP-STM reveals that interfacial Pd-InO nanostructures are created on the alloy surface by dissociative CO₂ adsorption under CO₂(g) environments even at 300 K. Synchrotron-based AP-XPS measurements support the idea that the observed CO₂ activation induces InO segregation onto the PdIn(111) surface by dissociated atomic oxygen from CO₂. After all, CO₂ gas molecules simultaneously adsorb onto the oxygen-terminated sites of the Pd-InO nanoclusters to produce carbonate species. Our in situ observations indicate that the restructuring metastable PdIn(111) alloy surface may provide active sites for efficient CO₂ activation, contributing to the rational catalyst design toward sustainable CO₂ utilizations.