A Multitechnique Study of C 2 H 4 Adsorption on a Model Single-Atom Rh 1 Catalyst.

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 C ₂ H ₄ with a model Rh/Fe ₃ O ₄ (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. C ₂ H ₄ adsorption is strongest at the 2-fold coordinated Rh ₁ 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. The adsorption energy at the 5-fold coordinated Rh sites is predicated to be -1.49 eV, but the superposition of this signal with that from small Rh clusters and additional heterogeneity leads to a broad C ₂ H ₄ desorption shoulder in TPD above room temperature.
Competing Interests: The authors declare no competing financial interest.
(© 2024 The Authors. Published by American Chemical Society.)