# Spectro-Microscopy of Individual Pt–Rh Core–Shell Nanoparticles during Competing Oxidation and Alloying

## TL;DR

This study uses high-resolution spectro-microscopy to observe how Rh behaves on Pt–Rh nanoparticles during oxidation and alloying processes.

## Contribution

The paper introduces a correlative spectro-microscopy approach to distinguish Rh oxidation, alloying, and sintering in real-time.

## Key findings

- Rh oxidation is more intense on the Rh layer over Pt-core than on nearby STO support.
- Rh diffuses into Pt at high temperatures, competing with oxidation.
- Rh/RhOx nanoparticles on STO sinter under oxidizing conditions.

## Abstract

The surface chemical composition of supported single
Pt–Rh
core–shell nanoparticles was studied to understand the Rh behavior
in oxidizing and reducing gas environments using spectro-microscopy
with high spatial resolution. We combined in situ X-ray photoemission electron microscopy with ex situ scanning electron-, atomic force-, and scanning Auger-microscopy
to distinguish Rh oxidation–reduction, dewetting–sintering,
and alloying–segregation during the course of the experiment.
A more than 20% higher Rh 3d5/2 oxide to metal photoemission
intensity ratio for the Rh layer on top of the Pt-core was found as
compared to the bare strontium titanate (STO) oxide catalyst support
in close vicinity, where Rh/RhO
x
nanoparticles
are forming. At elevated temperatures, Rh diffuses into the Pt particle,
and this alloying at the Pt metal surface competes with Rh oxidation,
whereas the Rh/RhO
x
nanoparticles on the
STO support are observed to sinter under identical oxidizing and temperature
environments. A nanoparticle facet-dependent analysis of selected
Pt-core nanoparticles suggests that Rh oxidation is most advanced
on a small nanoparticle with a low coordination top facet that we
indexed by electron backscatter diffraction, demonstrating the strength
of our correlative approach.