Hydrogen Activation via Dihydride Formation on a Rh ₁ /Fe ₃ O ₄ (001) Single‐Atom Catalyst

ABSTRACT Hydrogen activation is a key elementary step in catalytic hydrogenation. In heterogeneous catalysis, it usually proceeds through dissociative adsorption on metal nanoparticles followed by surface diffusion or spillover, whereas homogeneous catalysts activate H 2 through dihydride or dihydrogen intermediates at a single metal center. Here, we show that isolated Rh adatoms supported on Fe 3 O 4 (001) activate hydrogen through formation of a stable dihydride species without atomic H spillover. Temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and scanning tunneling microscopy collectively reveal strong (≈1 eV) hydrogen adsorption exclusively at isolated Rh 1 sites, while isotope‐exchange experiments further demonstrate that hydrogen remains localized. Density‐functional theory‐based calculations indicate a barrierless conversion from molecular H 2 to the dihydride, and random‐phase approximation calculations further confirm the relative stability of the dihydride. Together, these results show that single‐atom Rh sites cleave hydrogen through a dihydride pathway analogous to homogeneous complexes, establishing a mechanistic bridge between homogeneous and heterogeneous catalysis.