Unexpected Oxidation of Co Nanoparticles Under H 2 : X‐Ray‐Induced Water Radiolysis in NAP‐XPS Studies
Abstract
Cobalt nanoparticles exposed to 1 mbar H 2 during near‐ambient‐pressure x‐ray photoelectron spectroscopy oxidize instead of reducing, a result that contradicts thermodynamic expectations. Using beam‐free references, flux‐dependent operando measurements, depth‐resolved spectra, and thermal cycling, we show that x‐ray radiolysis of trace water (∼10 − 7 mbar) generates oxidizing species that dominate the surface chemistry of Co/SiO 2 . This radiolytic pathway produces a reproducible kinetic steady state in which ∼37% Co(II) persists even at 775 K under H 2 , and it drives complete oxidation under CO due to the absence of a hydrogen‐based reduction channel. Depth‐dependent data confirm that this oxidation is surface‐localized and directly controlled by photon flux, meaning the beam selectively modifies the layer that NAP‐XPS is intended to probe. These results establish photon flux, background water, and thermal history as active reaction parameters and define general constraints for operando NAP‐XPS on reducible, water‐reactive metals.
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BibTeX
@article{sharma2026unexpected,
title = {{Unexpected Oxidation of Co Nanoparticles Under H 2 : X‐Ray‐Induced Water Radiolysis in NAP‐XPS Studies}},
author = {Sagar Sharma and Michele de Rocco and Martine Trentesaux and Jean‐jacques Gallet and Fabrice Bournel and Ahmed Naitabdi and Anne‐sophie Mamede and Jean‐François Paul and Héloise Tissot},
journal = {ChemCatChem},
year = {2026},
month = jun,
doi = {10.1002/cctc.202501865},
url = {https://hal.science/hal-05803016v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Unexpected Oxidation of Co Nanoparticles Under H 2 : X‐Ray‐Induced Water Radiolysis in NAP‐XPS Studies
AU - Sagar Sharma
AU - Michele de Rocco
AU - Martine Trentesaux
AU - Jean‐jacques Gallet
AU - Fabrice Bournel
AU - Ahmed Naitabdi
AU - Anne‐sophie Mamede
AU - Jean‐François Paul
AU - Héloise Tissot
PY - 2026
DA - 2026/06/24
JO - ChemCatChem
DO - 10.1002/cctc.202501865
UR - https://hal.science/hal-05803016v1
AB - Cobalt nanoparticles exposed to 1 mbar H 2 during near‐ambient‐pressure x‐ray photoelectron spectroscopy oxidize instead of reducing, a result that contradicts thermodynamic expectations. Using beam‐free references, flux‐dependent operando measurements, depth‐resolved spectra, and thermal cycling, we show that x‐ray radiolysis of trace water (∼10 − 7 mbar) generates oxidizing species that dominate the surface chemistry of Co/SiO 2 . This radiolytic pathway produces a reproducible kinetic steady state in which ∼37% Co(II) persists even at 775 K under H 2 , and it drives complete oxidation under CO due to the absence of a hydrogen‐based reduction channel. Depth‐dependent data confirm that this oxidation is surface‐localized and directly controlled by photon flux, meaning the beam selectively modifies the layer that NAP‐XPS is intended to probe. These results establish photon flux, background water, and thermal history as active reaction parameters and define general constraints for operando NAP‐XPS on reducible, water‐reactive metals.
SN - 1867-3880
SN - 1867-3899
ER -