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

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 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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Category

Academic article

Language

English

Author(s)

Affiliation

  • SINTEF Industry / Materials and Nanotechnology
  • Lund University
  • Norwegian University of Science and Technology
  • Hydrogen Mem-Tech

Year

2022

Published in

Journal of Catalysis

ISSN

0021-9517

Volume

417

Page(s)

194 - 201

View this publication at Norwegian Research Information Repository