Hydrogen Activation via Dihydride Formation on a Rh1/Fe3O4(001) Single-Atom Catalyst

TL;DR

This study demonstrates that isolated Rh atoms on Fe3O4(001) can activate hydrogen by forming stable dihydride species without spillover, bridging mechanisms between homogeneous and heterogeneous catalysis.

Contribution

It reveals a novel single-atom catalysis mechanism where Rh adatoms activate H2 via dihydride formation, without spillover, supported by experimental and theoretical evidence.

Findings

Hydrogen adsorbs strongly at Rh1 sites (~1 eV)

H2 converts to dihydride without barriers

Dihydride is thermodynamically stable

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 H2 through dihydride or dihydrogen intermediates at a single metal center. Here, we show that isolated Rh adatoms supported on Fe3O4(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 (approximately 1 eV) hydrogen adsorption exclusively at isolated Rh1 sites, while isotope-exchange experiments further demonstrate that hydrogen remains localized. Density-functional theory based calculations indicate a barrierless conversion from molecular H2 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 and bind H2 through a dihydride pathway analogous to homogeneous complexes, establishing a mechanistic bridge between homogeneous and heterogeneous catalysis.