Adatom and nanoparticle dynamics on single-atom catalyst substrates

TL;DR

This study investigates how single-atom catalyst substrates influence nanoparticle dynamics, revealing how oxidizing and reducing conditions affect nanoparticle size and stability through atomic-level interactions.

Contribution

It introduces a generic model explaining Pt nanoparticle behavior on ceria surfaces under different atmospheres, integrating experimental and computational insights.

Findings

Pt single-atom sites control nanoparticle size in oxidizing environments.

Reducing atmospheres lead to nanoparticle growth due to depopulation of single-atom sites.

The model predicts conditions for stabilizing nanoparticle ensembles against Ostwald ripening.

Abstract

Single-atom catalysts represent an essential and ever-growing family of heterogeneous catalysts. Recent studies indicate that besides the valuable catalytic properties provided by single-atom active sites, the presence of single-atom sites on the catalyst substrates may significantly influence the population of supported metal nanoparticles coexisting with metal single atoms. Treatment of ceria-based single-atom catalysts in oxidizing or reducing atmospheres was proven to provide precise experimental control of the size of the supported Pt nanoparticles, and, correspondingly, control of catalyst activity and stability. Based on dedicated surface science experiments, ab-initio calculations and kinetic Monte-Carlo simulations we demonstrate that the morphology of Pt nanoparticle population on ceria surface is a result of a competition for Pt atoms between Pt single-atom sites and Pt nanoparticles. In oxidizing atmosphere, Pt single-atom sites provide strong bonding to single Pt atoms and Pt nanoparticles shrink. In reducing atmosphere, Pt single atom sites are depopulated and Pt nanoparticles grow. We formulate a generic model of Pt redispersion and coarsening on ceria substrates. Our model provides a unified atomic-level explanation for a variety of metal nanoparticle dynamic processes observed in single-atom catalysts under stationary or alternating oxidizing/reducing atmospheres, and allows to classify the conditions when nanoparticle ensembles on single-atom catalysts substrates can be stabilized against Ostwald ripening.