Reversed Hysteresis during CO Oxidation over Pd75Ag25(100)
Journal article, 2016
CO oxidation over Pd(100) and Pd75Ag25(100) has been investigated by a combination of near-ambient pressure X-ray photoelectron spectroscopy, quadrupole mass spectrometry, density functional theory calculations, and microkinetic modeling. For both surfaces, hysteresis is observed in the CO2 formation during the heating and cooling cycles. Whereas normal hysteresis with light-off temperature higher than extinction temperature is present for Pd(100), reversed hysteresis is observed for Pd75Ag25(100). The reversed hysteresis can be explained by dynamic changes in the surface composition. At the beginning of the heating ramp, the surface is rich in palladium, which gives a CO coverage that poisons the surface until the desorption rate becomes sufficiently high. The thermodynamic preference for an Ag-rich surface in the absence of adsorbates promotes diffusion of Ag from the bulk to the surface as CO desorbs. During the cooling ramp, an appreciable surface coverage is reached at temperatures too low for efficient diffusion of Ag back into the bulk. The high concentration of Ag in the surface leads to a high extinction temperature and, consequently, the reversed hysteresis.
pressure conditions
hysteresis
ray photoelectron-spectroscopy
DFT
carbon-monoxide oxidation
Pd75Ag25(100)
bimetallic catalysts
ultrahigh-vacuum
surface
microkinetic modeling
segregation
ambient
pd(111) surfaces
density-functional calculations
CO oxidation
Pd(100)
adsorption
hydrogen
pt-group metals
NAP-XPS
Chemistry
Author
V. R. Fernandes
Norwegian University of Science and Technology (NTNU)
Maxime van den Bossche
Competence Centre for Catalysis (KCK)
Chalmers, Physics, Chemical Physics
J. Knudsen
Lund University
M. H. Farstad
Norwegian University of Science and Technology (NTNU)
J. Gustafson
Lund University
H. J. Venvik
Norwegian University of Science and Technology (NTNU)
Henrik Grönbeck
Competence Centre for Catalysis (KCK)
Chalmers, Physics, Chemical Physics
A. Borg
Norwegian University of Science and Technology (NTNU)
ACS Catalysis
21555435 (eISSN)
Vol. 6 7 4154-4161Subject Categories
Physical Chemistry
Other Physics Topics
DOI
10.1021/acscatal.6b00658