Towards the surface hydroxyl species in CeO$_2$ nanoparticles

TL;DR

This study investigates the surface chemistry of CeO2 nanoparticles, revealing that hydroxyl groups, rather than Ce(III) states, influence their catalytic properties, through advanced experimental and computational analysis.

Contribution

The paper provides new insights into the surface hydroxyl species in CeO2 nanoparticles and clarifies the absence of Ce(III) at the surface, enhancing understanding of their chemical reactivity.

Findings

Ce(III) is absent at the surface of CeO2 nanoparticles even at 2 nm size.

Surface hydroxyl groups significantly influence nanoceria's chemical performance.

Advanced X-ray techniques combined with computations elucidate surface chemistry.

Abstract

Understanding the complex chemistry of functional nanomaterials is of fundamental importance. Controlled synthesis and characterization at the atomic level is essential to gain deeper insight into the unique chemical reactivity exhibited by many nanomaterials. Cerium oxide nanoparticles have many industrial and commercial applications,resulting from very strong catalytic, pro-and anti-oxidant activity. However, the identity of the active species and the chemical mechanisms imparted by nanoceria remain elusive, impeding the further development of new applications. Here, we explore the behavior of cerium oxide nanoparticles of different sizes at different temperatures and trace the electronic structure changes by state-of-the-art soft and hard X-ray experiments combined with computational methods. We confirm the absence of the Ce(III) oxidation state at the surface of CeO2nanoparticles, even for particles as small as 2 nm. Synchrotron X-ray absorption experiments at Ce L3and M5edges, combined with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS) and theoretical calculations demonstrate that in addition to the nanoceria charge stability, the formation of hydroxyl groups at the surface profoundly affects the chemical performance of these nanomaterials