# One Beam, Dual Insights: Simultaneous Chemical and Structural Changes in Nanopatterned Ceria under Reaction Conditions

## TL;DR

This study reveals how ceria interacts with hydrogen and CO2, showing changes in its chemical and structural properties using a novel X-ray technique.

## Contribution

The paper introduces a method using a single X-ray beam to track both chemical and structural changes in nanopatterned ceria under reaction conditions.

## Key findings

- Hydrogen incorporation increases the effective electron density in ceria, with a specific oxidation state order.
- Surface roughening occurs in a chemically specific manner under H2 and CO2 conditions.
- Combined X-ray techniques reveal insights missed by single-mode measurements in ceria–H2 transformations.

## Abstract

Ceria’s interaction with hydrogen can proceed
through multiple
chemical forms (hydride, hydroxyl, and oxyhydroxide-like), with consequences
for the oxidation state, density, and morphology that are rarely tracked
in the same evolving state. Here we show that under mild H2 (and H2 and CO2) environments nanopatterned
ceria undergoes oxidation-state changes accompanied by hydrogen incorporation
that increases the effective electron density, establishing the following
order: CeO2H
y
> CeO2 > CeO2–x
H
y
> CeO2–x
.
In parallel,
the surface roughens in a chemically specific manner, with the largest
changes coinciding with conditions where incorporated hydrogen is
driven to react with oxygen supplied either by air exposure between
experiments or by added CO2. We obtained these insights
by using a single X-ray beam to simultaneously perform ambient-pressure
X-ray photoelectron spectroscopy and grazing-incidence X-ray scattering
on the same sample spot. Single-mode measurements can miss key ceria–H2 transformations relevant to optimizing ceria-based hydrogenation
catalysts and supports.