A Multi-Technique Study of C2H4 Adsorption on a Model Single-Atom Rh1 Catalyst

TL;DR

This study combines experimental and computational techniques to analyze how ethylene (C2H4) interacts with a single-atom Rh catalyst on Fe3O4, revealing site-specific adsorption energies and migration behaviors.

Contribution

It provides detailed insights into the adsorption and migration of C2H4 on different Rh active sites, advancing understanding of single-atom catalysis mechanisms.

Findings

C2H4 binds most strongly to 2-fold Rh sites with -2.26 eV adsorption energy.

Desorption occurs at lower temperatures due to Rh migration into support sites.

Broad desorption shoulder indicates heterogeneity and cluster formation.

Abstract

Single-atom catalysts are potentially ideal model systems to investigate structure-function relationships in catalysis, if the active sites can be uniquely determined. In this work, we study the interaction of C2H4 with a model Rh/Fe3O4(001) catalyst that features 2-, 5-, and 6-fold coordinated Rh adatoms, as well as Rh clusters. Using multiple surface-sensitive techniques in combination with calculations of density functional theory (DFT), we follow the thermal evolution of the system and disentangle the behavior of the different species. C2H4 adsorption is strongest at the 2-fold coordinated Rh1 with a DFT-determined adsorption energy of -2.26 eV. However, desorption occurs at lower temperatures than expected because the Rh migrates into substitutional sites within the support, where the molecule is more weakly bound. Adsorption at the 5-fold coordinated Rh sites is predicated to -1.49 eV, but the superposition of this signal with that from small Rh clusters and additional heterogeneity leads to a broad C2H4 desorption shoulder in TPD above room temperature.