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.
bimetallic catalysts
adsorption
microkinetic modeling
hydrogen
pressure conditions
segregation
Pd(100)
NAP-XPS
pt-group metals
surface
Chemistry
density-functional calculations
ultrahigh-vacuum
ray photoelectron-spectroscopy
carbon-monoxide oxidation
hysteresis
CO oxidation
pd(111) surfaces
DFT
Pd75Ag25(100)
ambient
Author
V. R. Fernandes
Norges Teknisk-Naturvitenskapelige Universitet
Maxime van den Bossche
Chalmers, Physics, Chemical Physics
Competence Centre for Catalysis (KCK)
J. Knudsen
Lunds Universitet
M. H. Farstad
Norges Teknisk-Naturvitenskapelige Universitet
J. Gustafson
Lunds Universitet
H. J. Venvik
Norges Teknisk-Naturvitenskapelige Universitet
Henrik Grönbeck
Competence Centre for Catalysis (KCK)
Chalmers, Physics, Chemical Physics
A. Borg
Norges Teknisk-Naturvitenskapelige Universitet
ACS Catalysis
2155-5435 (eISSN)
Vol. 6 7 4154-4161Subject Categories (SSIF 2011)
Physical Chemistry
DOI
10.1021/acscatal.6b00658