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An unsupported Pd-rich GaPd2 sample in form of a thin film has been prepared by alternating layer deposition of Pd and Ga metal and was subsequently used as a structurally and chemically stable model system to clarify the catalytic properties of the unsupported intermetallic compound GaPd2 in methanol steam reforming (MSR). The sample revealed a slightly Pd-richer GaPd2 bulk composition of Ga28Pd72, as evidenced by EDX analysis, low-energy ion scattering, X-ray diffraction measurements, and depth profiling by in situ X-ray photoelectron spectroscopy. The latter additionally showed a high stability of GaPd2 both under methanol and oxidative methanol steam reforming conditions. No active redox chemistry of Ga species or other reaction-induced oxidative Ga surface segregation has been detected during catalytic MSR reaction. Corroborating these observations, corresponding catalytic experiments under methanol steam reforming conditions revealed only a, in comparison with elemental Pd, very small activity in methanol dehydrogenation (CO formation rate at maximum 0.019 mbar min(-1); 0.08 site(-1)-s(-1)). Unsupported thin film Pd-rich GaPd2 with the given surface and bulk stoichiometry must therefore be considered a poor methanol steam reforming/dehydrogenation catalyst. In oxidative steam reforming experiments, only total oxidation without significant H-2 formation has been observed. (C) 2013 Elsevier Inc. All rights reserved.

An unsupported Pd-rich GaPd2 sample in form of a thin film has been prepared by alternating layer deposition of Pd and Ga metal and was subsequently used as a structurally and chemically stable model system to clarify the catalytic properties of the unsupported intermetallic compound GaPd2 in methanol steam reforming (MSR). The sample revealed a slightly Pd-richer GaPd2 bulk composition of Ga28Pd72, as evidenced by EDX analysis, low-energy ion scattering, X-ray diffraction measurements, and depth profiling by in situ X-ray photoelectron spectroscopy. The latter additionally showed a high stability of GaPd2 both under methanol and oxidative methanol steam reforming conditions. No active redox chemistry of Ga species or other reaction-induced oxidative Ga surface segregation has been detected during catalytic MSR reaction. Corroborating these observations, corresponding catalytic experiments under methanol steam reforming conditions revealed only a, in comparison with elemental Pd, very small activity in methanol dehydrogenation (CO formation rate at maximum 0.019 mbar min(-1); 0.08 site(-1)-s(-1)). Unsupported thin film Pd-rich GaPd2 with the given surface and bulk stoichiometry must therefore be considered a poor methanol steam reforming/dehydrogenation catalyst. In oxidative steam reforming experiments, only total oxidation without significant H-2 formation has been observed. (C) 2013 Elsevier Inc. All rights reserved.

An unsupported Pd-rich GaPd2 sample in form of a thin film has been prepared by alternating layer deposition of Pd and Ga metal and was subsequently used as a structurally and chemically stable model system to clarify the catalytic properties of the unsupported intermetallic compound GaPd2 in methanol steam reforming (MSR). The sample revealed a slightly Pd-richer GaPd2 bulk composition of Ga28Pd72, as evidenced by EDX analysis, low-energy ion scattering, X-ray diffraction measurements, and depth profiling by in situ X-ray photoelectron spectroscopy. The latter additionally showed a high stability of GaPd2 both under methanol and oxidative methanol steam reforming conditions. No active redox chemistry of Ga species or other reaction-induced oxidative Ga surface segregation has been detected during catalytic MSR reaction. Corroborating these observations, corresponding catalytic experiments under methanol steam reforming conditions revealed only a, in comparison with elemental Pd, very small activity in methanol dehydrogenation (CO formation rate at maximum 0.019 mbar min(-1); 0.08 site(-1)-s(-1)). Unsupported thin film Pd-rich GaPd2 with the given surface and bulk stoichiometry must therefore be considered a poor methanol steam reforming/dehydrogenation catalyst. In oxidative steam reforming experiments, only total oxidation without significant H-2 formation has been observed. (C) 2013 Elsevier Inc. All rights reserved.

An unsupported Pd-rich GaPd2 sample in form of a thin film has been prepared by alternating layer deposition of Pd and Ga metal and was subsequently used as a structurally and chemically stable model system to clarify the catalytic properties of the unsupported intermetallic compound GaPd2 in methanol steam reforming (MSR). The sample revealed a slightly Pd-richer GaPd2 bulk composition of Ga28Pd72, as evidenced by EDX analysis, low-energy ion scattering, X-ray diffraction measurements, and depth profiling by in situ X-ray photoelectron spectroscopy. The latter additionally showed a high stability of GaPd2 both under methanol and oxidative methanol steam reforming conditions. No active redox chemistry of Ga species or other reaction-induced oxidative Ga surface segregation has been detected during catalytic MSR reaction. Corroborating these observations, corresponding catalytic experiments under methanol steam reforming conditions revealed only a, in comparison with elemental Pd, very small activity in methanol dehydrogenation (CO formation rate at maximum 0.019 mbar min(-1); 0.08 site(-1)-s(-1)). Unsupported thin film Pd-rich GaPd2 with the given surface and bulk stoichiometry must therefore be considered a poor methanol steam reforming/dehydrogenation catalyst. In oxidative steam reforming experiments, only total oxidation without significant H-2 formation has been observed. (C) 2013 Elsevier Inc. All rights reserved.

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 similar to 4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a similar to 1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar "Cu-like" electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart. Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100% between 493 and 550 K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 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 CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, 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-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water-gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst. (C) 2012 Elsevier Inc. All rights reserved.

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 CO2 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 PdxGa/Ga2O3 systems, which exhibit high CO2 selectivity in a broad temperature range. In contrast, corresponding experiments starting on the purely bimetallic model surface in oxidative methanol reforming yielded high CO2 selectivity already at low temperatures (similar to 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 CO2. (c) 2012 Elsevier Inc. All rights reserved.

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 CO2 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 PdxGa/Ga2O3 systems, which exhibit high CO2 selectivity in a broad temperature range. In contrast, corresponding experiments starting on the purely bimetallic model surface in oxidative methanol reforming yielded high CO2 selectivity already at low temperatures (similar to 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 CO2. (c) 2012 Elsevier Inc. All rights reserved.

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 similar to 4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a similar to 1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar "Cu-like" electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart. Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100% between 493 and 550 K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 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 CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, 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-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water-gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst. (C) 2012 Elsevier Inc. All rights reserved.

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 similar to 4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a similar to 1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar "Cu-like" electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart. Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100% between 493 and 550 K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 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 CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, 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-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water-gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst. (C) 2012 Elsevier Inc. All rights reserved.

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 CO2 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 PdxGa/Ga2O3 systems, which exhibit high CO2 selectivity in a broad temperature range. In contrast, corresponding experiments starting on the purely bimetallic model surface in oxidative methanol reforming yielded high CO2 selectivity already at low temperatures (similar to 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 CO2. (c) 2012 Elsevier Inc. All rights reserved.

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 similar to 4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a similar to 1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar "Cu-like" electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart. Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100% between 493 and 550 K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 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 CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, 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-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water-gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst. (C) 2012 Elsevier Inc. All rights reserved.

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 CO2 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 PdxGa/Ga2O3 systems, which exhibit high CO2 selectivity in a broad temperature range. In contrast, corresponding experiments starting on the purely bimetallic model surface in oxidative methanol reforming yielded high CO2 selectivity already at low temperatures (similar to 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 CO2. (c) 2012 Elsevier Inc. All rights reserved.