Spatially Resolved Geometric and Electronic Structure at Ru-TiO₂ Interface by EELS at Very High Energy Losses

The interfacial structure between metal nanoparticles and oxide supports critically influences catalytic performance, yet resolving their local geometric and electronic features at the atomic scale remains challenging. In this study, aberration-corrected scanning transmission electron microscopy (STEM) combined with monochromated electron energy loss spectroscopy (EELS) is employed at very high energy losses (>2000 eV) to investigate Ru-TiO₂ interfaces in catalysts with distinct TiO₂ crystalline phases. High-resolution STEM and EELS mapping reveal phase-dependent TiO_x overlayer structures: atomically thin in Ru/P25-TiO₂, and thicker amorphous or island-like in rutile- and anatase-supported counterparts. Fine-structure analysis of Ti-L₂,₃ and O-K edges shows that Ru/P25-TiO₂ exhibits a lower Ti³⁺ fraction (30.2%) and reduced Ru-to-TiO₂ charge transfer, which enhances CO adsorption and promotes its hydrogenation to CH₄. Extended energy-loss fine structure (EXELFS) analysis of Ti-K spectra further discloses elongated Ti─O bonds (1.86 vs bulk 1.83 Å), indicating the formation of Ti³⁺-O_V-Ru^δ+ interfacial sites. These interfacial characteristics correlate with superior CO₂ hydrogenation performance, achieving >99% CO₂ conversion and >96% CH₄ selectivity. This work highlights the power of high-resolution EELS and EXELFS in unveiling sub-nanometer interfacial structures and offers a new strategy for rational catalyst design through control of metal-support interactions.