In situ XPS study of methanol reforming on PdGa near-surface intermetallic phases

Rameshan, Christoph; Stadlmayr, Werner; Penner, Simon; Lorenz, Harald; Hävecker, Michael; Blume, Raoul; Rocha, Túlio C. R.; Teschner, Detre; Knop‐Gericke, Axel; Schlögl, Robert; Zemlyanov, Dmitry; Memmel, N.; Klötzer, Bernhard

doi:10.1016/j.jcat.2012.03.009

Cited by 51 publications

(69 citation statements)

References 25 publications

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“…[60,61] Subsequent catalytic experiments on the MSR reaction revealed that multilayered PdGa NSIP was a poor, unselective catalyst, owing to its inability to activate water, as evidenced by the parallel, unselective production of mainly CO, some HCHO, and a small amount of CO 2 ( Figure 6). This result is in contrast to our MSR results on both supported and thinfilm PdGa/b-Ga 2 O 3 and Pd 2 Ga/b-Ga 2 O 3 [67,68] , as well as on the related PdZn NSIP, [60,61] which all showed a temperature range for increased CO 2 selectivity above about 530 K. [66] However, Figure 6, bottom, shows that the PdGa NSIP is capable of efficient oxygen activation, because, under oxidative steam-reforming conditions, a large amount of CO 2 is observed at low temperatures (491 K).…”

Section: Insights Into the Pdàga Systemcontrasting

confidence: 99%

“…The water-activating role of the bimetalÀoxide contact became even more clear in our investigation of PdGa near-surface intermetallic phases ( Figure 5). [66] In situ XPS spectroscopy during the MSR reaction revealed no signs of (hydr)oxide species, Figure 2. Temperature-programmed MSR on a multilayer PdZn (1:1) alloy on Pd foil (top) versus the MSR on a "Zn-lean" monolayer PdZn surface and the MSR on clean Pd foil (bottom).…”

Section: Insights Into the Pdàga Systemmentioning

confidence: 99%

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From Oxide‐Supported Palladium to Intermetallic Palladium Phases: Consequences for Methanol Steam Reforming

et al. 2013

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This Minireview summarizes the fundamental results of a comparative inverse-model versus real-model catalyst approach toward methanol steam reforming (MSR) on the highly CO₂-selective H₂-reduced states of supported Pd/ZnO, Pd/Ga₂O3, and Pd/In₂O3 catalysts. Our model approach was extended to the related Pd/GeO₂ and Pd/SnO₂ systems, which showed previously unknown MSR performance. This approach allowed us to determine salient CO₂-selectivity-guiding structural and electronic effects on the molecular level, to establish a knowledge-based approach for the optimization of CO₂ selectivity. Regarding the inverse-model catalysts, in situ X-ray photoelectron spectroscopy (in situ XPS) studies on near-surface intermetallic PdZn, PdGa, and PdIn phases (NSIP), as well as bulk Pd₂Ga, under realistic MSR conditions were performed alongside catalytic testing. To highlight the importance of a specifically prepared bulk intermetallic[BOND]oxide interface, unsupported bulk intermetallic compounds of Pd_xGa_y were chosen as additional MSR model compounds, which allowed us to clearly deduce, for example, the water-activating role of the special Pd₂Ga-β-Ga₂O₃ intermetallic[BOND]oxide interaction. The inverse-model studies were complemented by their related “real-model” experiments. Structure–activity and structure–selectivity correlations were performed on epitaxially ordered PdZn, Pd₅Ga₂, PdIn, Pd₃Snv, and Pd₂Ge nanoparticles that were embedded in thin crystalline films of their respective oxides. The reductively activated “thin-film model catalysts” that were prepared by sequential Pd and oxide deposition onto NaCl(001) exhibited the required large bimetal[BOND]oxide interface and the highly epitaxial ordering that was required for (HR)TEM studies and for identification of the structural and catalytic (bi)metal[BOND]support interactions. To fully understand the bimetal[BOND]support interactions in the supported systems, our studies were extended to the MeOH- and formaldehyde-reforming properties of the clean supporting oxides. From a direct comparison of the “isolated” MSR performance of the purely bimetallic surfaces to that of the “isolated” oxide surfaces and of the “bimetal[BOND]oxide contact” systems, a pronounced “bimetal[BOND]oxide synergy” toward optimum CO2 activity/selectivity was most evident. Moreover, the system-specific mechanisms that led to undesired CO formation and to spoiling of the CO2 selectivity could be extracted

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Section: Insights Into the Pdàga Systemcontrasting

confidence: 99%

Section: Insights Into the Pdàga Systemmentioning

confidence: 99%

From Oxide‐Supported Palladium to Intermetallic Palladium Phases: Consequences for Methanol Steam Reforming

et al. 2013

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“…11 However, these early results were taken only in a limited coverage/temperature range (∼1.5 ML, 500 K) where buckling is close to zero.…”

Section: Ga/pd(111)mentioning

confidence: 99%

Alloying and Structure of Ultrathin Gallium Films on the (111) and (110) Surfaces of Palladium

Stadlmayr¹,

Huber²,

Penner³

et al. 2013

J. Phys. Chem. C

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Growth, thermal stability, and structure of ultrathin gallium films on Pd(111) and Pd(110) are investigated by low-energy ion scattering and low-energy electron diffraction. Common to both surface orientations are growth of disordered Ga films at coverages of a few monolayers (T = 150 K), onset of alloy formation at low temperatures (T ≈ 200 K), and formation of a metastable, mostly disordered 1:1 surface alloy at temperatures around 400–500 K. At higher temperatures a Ga surface fraction of ∼0.3 is slightly stabilized on Pd(111), which we suggest to be related to the formation of Pd2Ga bulk-like films. While on Pd(110) only a Pd-up/Ga-down buckled surface was observed, an inversion of buckling was observed on Pd(111) upon heating. Similarities and differences to the related Zn/Pd system are discussed.

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“…To correlate with the structure-insensitive total oxidation of methanol with O 2 toward CO 2 and water at low temperatures on the PdGa NSIP [2], two types of reforming reactions were studied in situ, namely “water-only” methanol steam reforming (MSR), corresponding to the “ideal” reaction CH 3 OH + H 2 O → CO 2 + 3H 2 , and oxidative steam reforming (OSR), whereby a certain added amount of O 2 may give rise to H 2 -formation stoichiometries ranging from partial methanol oxidation (CH 3 OH + 1/2 O 2 → CO 2 + 2H 2 ) to total oxidation (CH 3 OH + 3/2 O 2 → CO 2 + 2H 2 O). The interest in comparing MSR and OSR is basically derived from the fact that admission of a defined oxygen partial pressure to a methanol–water mixture is common to additionally suppress CO formation in the product stream by further CO oxidation and to compensate for the endothermicity of the pure methanol steam reforming reaction.…”

Section: Introductionmentioning

confidence: 99%

CO2-selective methanol steam reforming on In-doped Pd studied by in situ X-ray photoelectron spectroscopy

Rameshan

Lorenz

Mayr

et al. 2012

Journal of Catalysis

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Graphical abstractPdIn intermetallic phases can be switched in methanol steam reforming between a CO2-selective multilayer and an In-diluted phase by annealing at 453 K or 623 K.Highlights► A multilayer Pd1In1 phase in MSR is highly CO2-selective between 493 and 623 K. ► An In-diluted PdIn intermetallic phase yields CO formation via full methanol dehydrogenation. ► Higher reaction temperatures are needed for comparable CO2-TOF values as on supported PdIn/In2O3. ► A bimetal-oxide synergism for efficient CO2 formation is operative.

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In situ XPS study of methanol reforming on PdGa near-surface intermetallic phases

Cited by 51 publications

References 25 publications

From Oxide‐Supported Palladium to Intermetallic Palladium Phases: Consequences for Methanol Steam Reforming

From Oxide‐Supported Palladium to Intermetallic Palladium Phases: Consequences for Methanol Steam Reforming

Alloying and Structure of Ultrathin Gallium Films on the (111) and (110) Surfaces of Palladium

CO2-selective methanol steam reforming on In-doped Pd studied by in situ X-ray photoelectron spectroscopy

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