title: In situ XPS study of methanol reforming on PdGa near-surface intermetallic phases.
abstract: In situ X-ray photoelectron spectroscopy and low-energy ion scattering were used to study the preparation, (thermo)chemical and catalytic properties of 1:1 PdGa intermetallic near-surface phases. Deposition of several multilayers of Ga metal and subsequent annealing to 503-523 K led to the formation of a multi-layered 1:1 PdGa near-surface state without desorption of excess Ga to the gas phase. In general, the composition of the PdGa model system is much more variable than that of its PdZn counterpart, which results in gradual changes of the near-surface composition with increasing annealing or reaction temperature.In contrast to near-surface PdZn, in methanol steam reforming, no temperature region with pronounced CO(2) selectivity was observed, which is due to the inability of purely intermetallic PdGa to efficiently activate water. This allows to pinpoint the water-activating role of the intermetallic/support interface and/or of the oxide support in the related supported Pd(x)Ga/Ga(2)O(3) systems, which exhibit high CO(2) selectivity in a broad temperature range. In contrast, corresponding experiments starting on the purely bimetallic model surface in oxidative methanol reforming yielded high CO(2) selectivity already at low temperatures (∼460 K), which is due to efficient O(2) activation on PdGa. In situ detected partial and reversible oxidative Ga segregation on intermetallic PdGa is associated with total oxidation of intermediate C(1) oxygenates to CO(2).
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Rameshan
authors.forename: Werner
authors.initials: W
authors.lastname: Stadlmayr
authors.forename: Simon
authors.initials: S
authors.lastname: Penner
authors.forename: Harald
authors.initials: H
authors.lastname: Lorenz
authors.forename: Lukas
authors.initials: L
authors.lastname: Mayr
authors.forename: Michael
authors.initials: M
authors.lastname: Hävecker
authors.forename: Raoul
authors.initials: R
authors.lastname: Blume
authors.forename: Tulio
authors.initials: T
authors.lastname: Rocha
authors.forename: Detre
authors.initials: D
authors.lastname: Teschner
authors.forename: Axel
authors.initials: A
authors.lastname: Knop-Gericke
authors.forename: Robert
authors.initials: R
authors.lastname: Schlögl
authors.forename: Dmitry
authors.initials: D
authors.lastname: Zemlyanov
authors.forename: Norbert
authors.initials: N
authors.lastname: Memmel
authors.forename: Bernhard
authors.initials: B
authors.lastname: Klötzer