TY - JOUR
T1 - In situ XPS study of Pd(1 1 1) oxidation at elevated pressure, Part 2
T2 - Palladium oxidation in the 10-1 mbar range
AU - Gabasch, Harald
AU - Unterberger, Werner
AU - Hayek, Konrad
AU - Klötzer, Bernhard
AU - Kleimenov, Evgueni
AU - Teschner, Detre
AU - Zafeiratos, Spiros
AU - Hävecker, Michael
AU - Knop-Gericke, Axel
AU - Schlögl, Robert
AU - Han, Jinyi
AU - Ribeiro, Fabio H.
AU - Aszalos-Kiss, Balazs
AU - Curtin, Teresa
AU - Zemlyanov, Dmitry
PY - 2006/8/1
Y1 - 2006/8/1
N2 - The oxidation of the Pd(1 1 1) surface was studied by in situ XPS during heating and cooling in 0.4 mbar O2. The in situ XPS data were complemented by ex situ TPD results. A number of oxygen species and oxidation states of palladium were observed in situ and ex situ. At 430 K, the Pd(1 1 1) surface was covered by a 2D oxide and by a supersaturated Oads layer. The supersaturated Oads layer transforms into the Pd5O4 phase upon heating and disappears completely at approximately 470 K. Simultaneously, small clusters of PdO, PdO seeds, are formed. Above 655 K, the bulk PdO phase appears and this phase decomposes completely at 815 K. Decomposition of the bulk oxide is followed by oxygen dissolution in the near-surface region and in the bulk. The oxygen species dissolved in the bulk is more favoured at high temperatures because oxygen cannot accumulate in the near-surface region and diffusion shifts the equilibrium towards the bulk species. The saturation of the bulk "reservoir" with oxygen leads to increasing the uptake of the near-surface region species. Surprisingly, the bulk PdO phase does not form during cooling in 0.4 mbar O2, but the Pd5O4 phase appears below 745 K. This is proposed to be due to a kinetic limitation of PdO formation because at high temperature the rate of PdO seed formation is compatible with the rate of decomposition.
AB - The oxidation of the Pd(1 1 1) surface was studied by in situ XPS during heating and cooling in 0.4 mbar O2. The in situ XPS data were complemented by ex situ TPD results. A number of oxygen species and oxidation states of palladium were observed in situ and ex situ. At 430 K, the Pd(1 1 1) surface was covered by a 2D oxide and by a supersaturated Oads layer. The supersaturated Oads layer transforms into the Pd5O4 phase upon heating and disappears completely at approximately 470 K. Simultaneously, small clusters of PdO, PdO seeds, are formed. Above 655 K, the bulk PdO phase appears and this phase decomposes completely at 815 K. Decomposition of the bulk oxide is followed by oxygen dissolution in the near-surface region and in the bulk. The oxygen species dissolved in the bulk is more favoured at high temperatures because oxygen cannot accumulate in the near-surface region and diffusion shifts the equilibrium towards the bulk species. The saturation of the bulk "reservoir" with oxygen leads to increasing the uptake of the near-surface region species. Surprisingly, the bulk PdO phase does not form during cooling in 0.4 mbar O2, but the Pd5O4 phase appears below 745 K. This is proposed to be due to a kinetic limitation of PdO formation because at high temperature the rate of PdO seed formation is compatible with the rate of decomposition.
KW - Chemisorption
KW - High-pressure XPS
KW - Low index single crystal surfaces
KW - Oxidation
KW - Oxygen
KW - Palladium
KW - Single crystal surfaces
KW - Surface chemical reaction
KW - X-ray photoelectron spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=33745976176&partnerID=8YFLogxK
U2 - 10.1016/j.susc.2006.05.029
DO - 10.1016/j.susc.2006.05.029
M3 - Article
AN - SCOPUS:33745976176
SN - 0039-6028
VL - 600
SP - 2980
EP - 2989
JO - Surface Science
JF - Surface Science
IS - 15
ER -