(177e) Metal-Metal Oxide Interaction Induced Yolk-Shell Nanocrystals for Acetylene Semihydrogenation

Metal-metal oxide interactions play an important role in heterogeneous catalysis, and therefore, have spurred tremendous interest in the in-depth understanding and investigation of the strength, stability, and dynamic evolution of such interactions. Herein, we synthesize a series of core-shell metal-iron oxide nanocrystals (M-FeO_x, M = Pd, Pt, Au) and employ both in situ and ex situ electron microscopy and X-ray absorption spectroscopy (XAS) to study the atomic and nanoscopic dynamic M-FeO_x interactions under reductive atmosphere (H₂) at elevated temperatures. The H₂-treated M-FeO_x core-shell structures all evolved into yolk-shell structures (denoted as M-FeO_x-H). However, dissimilar metal-metal oxide interactions have been observed among the three M-FeO_x-H systems. We show that Pd core interacts strongly with the FeO_x shell after the H₂ treatment, featured by the formation of Pd single atoms on the FeO_x shell and increased Pd-Fe bonding. Meanwhile the Pt core transforms into an ordered PtFe intermetallic structure and Pt single atoms are anchored on the FeO_x shell immediately upon the coating of FeO_x. The PtFe intermetallic core is thermodynamically stable without bonding change during the post-synthesis H₂ treatment. In contrast, Au-FeO_x-H forms negligible Au-Fe bonding nor Au single atoms. Finally, we conduct comprehensive catalytic tests of M-FeO_x-H systems on acetylene semihydrogenation reaction. Among the three systems, Pd-FeO_x-H exhibits best catalytic performance, achieving 100% acetylene conversion and 86.5% ethylene selectivity at 60 °C. Our work not only depicts the dynamic evolution of the metal-metal oxide interactions of M-FeO_x systems but also offers a unique method to synthesize yolk-shell nanocomposites consisting single atoms and intermetallic alloys. The resulting M-FeO_x-H yolk-shell nanocrystals can be employed as excellent catalyst for reactions including but not limited to alkyne hydrogenation.