title: CO(2)-selective methanol steam reforming on In-doped Pd studied by in situ X-ray photoelectron spectroscopy.
abstract: In situ X-ray photoelectron spectroscopy (in situ XPS) was used to study the structural and catalytic properties of Pd-In near-surface intermetallic phases in correlation with previously studied PdZn and PdGa.Room temperature deposition of ∼4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a ∼1:1 Pd/In near-surface multilayer intermetallic phase. This Pd(1)In(1) phase exhibits a similar "Cu-like" electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd(1)Zn(1) counterpart.Catalytic characterization of the multilayer Pd(1)In(1) phase in MSR yielded a CO(2)-selectivity of almost 100% between 493 and 550 K. In contrast to previously studied In(2)O(3)-supported PdIn nanoparticles and pure In(2)O(3), intermediate formaldehyde is only partially converted to CO(2) using this Pd(1)In(1) phase. Strongly correlated with PdZn, on an In-diluted PdIn intermetallic phase with "Pd-like" electronic structure, prepared by thermal annealing at 623 K, methanol steam reforming is suppressed and enhanced CO formation via full methanol dehydrogenation is observed.To achieve CO(2)-TOF values on the isolated Pd(1)In(1) intermetallic phase as high as on supported PdIn/In(2)O(3), at least 593 K reaction temperature is required. A bimetal-oxide synergism, with both bimetallic and oxide synergistically contributing to the observed catalytic activity and selectivity, manifests itself by accelerated formaldehyde-to-CO(2) conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd(1)In(1) inhibited inverse water-gas-shift reaction on In(2)O(3) and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO(2)-selectivity of the supported catalyst.
authors.affiliation: Institute of Physical Chemistry, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria ; Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, D-14195 Berlin, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Rameshan
authors.forename: Harald
authors.initials: H
authors.lastname: Lorenz
authors.forename: Lukas
authors.initials: L
authors.lastname: Mayr
authors.forename: Simon
authors.initials: S
authors.lastname: Penner
authors.forename: Dmitry
authors.initials: D
authors.lastname: Zemlyanov
authors.forename: Rosa
authors.initials: R
authors.lastname: Arrigo
authors.forename: Michael
authors.initials: M
authors.lastname: Haevecker
authors.forename: Raoul
authors.initials: R
authors.lastname: Blume
authors.forename: Axel
authors.initials: A
authors.lastname: Knop-Gericke
authors.forename: Robert
authors.initials: R
authors.lastname: Schlögl
authors.forename: Bernhard
authors.initials: B
authors.lastname: Klötzer