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

## TL;DR

This study shows that hydrogen activates on a single-atom rhodium catalyst by forming a stable dihydride, without hydrogen spillover, bridging homogeneous and heterogeneous catalysis.

## Contribution

The paper reveals a dihydride-based hydrogen activation mechanism on a single-atom catalyst, similar to homogeneous systems, without spillover.

## Key findings

- Hydrogen adsorbs strongly at isolated Rh1 sites without spillover onto Fe3O4.
- Dihydride formation is confirmed through experiments and calculations as the hydrogen activation pathway.
- The dihydride species is stable and desorbs as H2 or D2 during annealing.

## 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 (≈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 hydrogen through a dihydride pathway analogous to homogeneous complexes, establishing a mechanistic bridge between homogeneous and heterogeneous catalysis.

Deuterium (hydrogen) adsorption on single‐atom Rh1/Fe3O4(001) catalyst does not induce D (H) spillover onto the reducible Fe3O4 support. Instead, a Rh1‐dihydride (Rh−2D or Rh−2H) species forms and D2 or H2desorbs during annealing.