In Situ X-ray Absorption Spectroscopic Study of Fe@Fe_xO_y/Pd and Fe@Fe_xO_y/Cu Nanoparticle Catalysts Prepared by Galvanic Exchange Reactions

Fe@Fe x O y core–shell nanoparticles have been previously shown to be a versatile support for catalytic metals such as Pd and Cu. However, the resulting structure, metal speciation, and performance of such catalysts in catalytic reactions are still poorly understood. Herein, we synthesize Fe@Fe x O y -supported Pd and Cu nanoparticles by controlling the molar ratios of Fe@Fe x O y nanoparticles to Pd 2+ or Cu 2+ species. Scanning transmission electron microscopy analyses show that Pd or Cu NPs are deposited on the exterior shell of the Fe@Fe x O y nanoparticles. In situ X-ray absorption near-edge structure (XANES) spectra were used to follow the formation processes of Fe@Fe x O y /Pd and Fe@Fe x O y /Cu nanoparticles and the performance of Fe@Fe x O y /Pd nanoparticles for Suzuki–Miyaura cross-coupling reactions. The results show that different molar ratios of Fe@Fe x O y nanoparticles to Pd 2+ or Cu 2+ lead to different morphologies of the resulting supported-NP structures. In situ XANES results show that Fe@Fe x O y nanoparticles can effectively fully reduce Pd or Cu salts over the course of ∼20 min to give small Pd or larger Cu nanoparticles on the surface and can also rereduce oxidized Pd in Suzuki–Miyaura cross-coupling reactions.