(169as) Adsorbate Effects on the Mobility of Single Atom Catalysts: Using DFT to Map out Diffusion Potential Energy Surfaces

Representing a novel frontier in heterogeneous catalysis, Single-atom catalysts (SACs) supported on metal oxide surfaces exhibit remarkable potential for catalyzing hydrodeoxygenation reactions, boasting high activity and selectivity. However, the pronounced mobility of SACs renders them susceptible to aggregation, resulting in catalyst deactivation (Yang et al., 2013). Our study investigates the underlying mechanisms governing the aggregation behavior of SACs in the presence of atomic adsorbates. Employing density functional theory (DFT), we develop a comprehensive and explicit approach to enumerate the full Potential Energy Surface (PES), accounting for both metal atoms and adsorbates, to understand how adsorbates influence metal atom diffusivity. Our preliminary results unveil intriguing dynamics: while the adsorption of hydrogen on single metal atoms enhances surface mobility, the transition to more reduced species, characterized by hydrogen adsorption on the surface leading to hydroxyl group formation, introduces a physical and chemical barrier to diffusion, impeding metal atom mobility even in the hydride form. Furthermore, under elevated hydrogen pressures, increased hydrogen uptake triggers the formation of surface oxygen vacancies on the metal oxide. We propose that these vacancies act as nucleation sites, capturing single atoms and curtailing surface diffusion. Our findings illuminate the complex relationship between atomic adsorbates and SACs aggregation behavior, offering insights crucial for tailored design strategies to mitigate catalyst deactivation in hydrodeoxygenation processes.

_{Yang, X.-F., Wang, A., Qiao, B., Li, J., Liu, J., & Zhang, T. (2013). Single-Atom Catalysts: A New Frontier in Heterogeneous Catalysis. Accounts of Chemical Research, 46(8), 1740–1748. https://doi.org/10.1021/ar300361m}