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Activity and segregation behavior of Pd75%Ag25%(1 1 1) during CO oxidation – An in situ NAP-XPS investigation

Svenum, Ingeborg Helene ; Strømsheim, Marie D. ; Knudsen, Jan LU and Venvik, Hilde J. (2023) In Journal of Catalysis 417. p.194-201
Abstract

The surface reactivity during CO oxidation over Pd(1 1 1) and Pd75%Ag25%(1 1 1) single crystals has been investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) under excess oxygen conditions (p ≈ 2 mbar, O2:CO=10). The (√6×√6) Pd5O4 surface oxide is present on Pd(1 1 1) when the surface is highly active under the applied conditions. The CO2 formation profile follows a hysteresis upon temperature cycling between 150 and 450 °C that depends on the temperature ramp rate. The behavior is different for Pd75%Ag25%(1 1 1), with the CO2 formation rate considerably lower, no surface oxide and only chemisorbed oxygen... (More)

The surface reactivity during CO oxidation over Pd(1 1 1) and Pd75%Ag25%(1 1 1) single crystals has been investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) under excess oxygen conditions (p ≈ 2 mbar, O2:CO=10). The (√6×√6) Pd5O4 surface oxide is present on Pd(1 1 1) when the surface is highly active under the applied conditions. The CO2 formation profile follows a hysteresis upon temperature cycling between 150 and 450 °C that depends on the temperature ramp rate. The behavior is different for Pd75%Ag25%(1 1 1), with the CO2 formation rate considerably lower, no surface oxide and only chemisorbed oxygen present at the surface at high temperature, reversible scrambling of the (near) surface Pd/(Pd+Ag) ratio, and no hysteresis behavior observed. The results suggest that the reactant activation is affected by both surface composition and surface termination, i.e. mechanistically different on Pd75%Ag25%(1 1 1) than Pd(1 1 1), and less efficient on (1 1 1) as compared to the (1 0 0) alloy counterpart.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Bimetallic catalysis, Carbon monoxide oxidation, Palladium, Segregation, Silver, Single crystal surface
in
Journal of Catalysis
volume
417
pages
8 pages
publisher
Elsevier
external identifiers
  • scopus:85145587529
ISSN
0021-9517
DOI
10.1016/j.jcat.2022.11.038
language
English
LU publication?
yes
id
1eab6e8f-7af8-49b3-aa3f-a83029803a6c
date added to LUP
2023-02-13 10:27:39
date last changed
2025-10-14 12:58:10
@article{1eab6e8f-7af8-49b3-aa3f-a83029803a6c,
  abstract     = {{<p>The surface reactivity during CO oxidation over Pd(1 1 1) and Pd<sub>75%</sub>Ag<sub>25%</sub>(1 1 1) single crystals has been investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) under excess oxygen conditions (p ≈ 2 mbar, O<sub>2</sub>:CO=10). The (√6×√6) Pd<sub>5</sub>O<sub>4</sub> surface oxide is present on Pd(1 1 1) when the surface is highly active under the applied conditions. The CO<sub>2</sub> formation profile follows a hysteresis upon temperature cycling between 150 and 450 °C that depends on the temperature ramp rate. The behavior is different for Pd<sub>75%</sub>Ag<sub>25%</sub>(1 1 1), with the CO<sub>2</sub> formation rate considerably lower, no surface oxide and only chemisorbed oxygen present at the surface at high temperature, reversible scrambling of the (near) surface Pd/(Pd+Ag) ratio, and no hysteresis behavior observed. The results suggest that the reactant activation is affected by both surface composition and surface termination, i.e. mechanistically different on Pd<sub>75%</sub>Ag<sub>25%</sub>(1 1 1) than Pd(1 1 1), and less efficient on (1 1 1) as compared to the (1 0 0) alloy counterpart.</p>}},
  author       = {{Svenum, Ingeborg Helene and Strømsheim, Marie D. and Knudsen, Jan and Venvik, Hilde J.}},
  issn         = {{0021-9517}},
  keywords     = {{Bimetallic catalysis; Carbon monoxide oxidation; Palladium; Segregation; Silver; Single crystal surface}},
  language     = {{eng}},
  pages        = {{194--201}},
  publisher    = {{Elsevier}},
  series       = {{Journal of Catalysis}},
  title        = {{Activity and segregation behavior of Pd<sub>75%</sub>Ag<sub>25%</sub>(1 1 1) during CO oxidation – An in situ NAP-XPS investigation}},
  url          = {{http://dx.doi.org/10.1016/j.jcat.2022.11.038}},
  doi          = {{10.1016/j.jcat.2022.11.038}},
  volume       = {{417}},
  year         = {{2023}},
}