An exafs study of the influence of the metal particle size, nature of support, and adsorption of H2 and CO on the structure of palladium catalysts

Kochubey, D.I.; Feodorov, V. K.; Williams, C.; Nogin, Yu. N.; Stenin, M. V.; Ryndin, Yu. A.; Thomas, John Meurig; Zamaraev, K. I.

doi:10.1007/bf00765176

Cited by 7 publications

(6 citation statements)

References 2 publications

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“…For example, for Pd particles with sizes of 1–2 nm on multiple supports at atmospheric pressure and room temperature, lattice expansions of ≤ 1.8% have been reported . For 5 wt % Pd/Al 2 O 3 with sizes of ≈5 nm, an expansion of 3.7% was found, and for Pd/SiO 2 with sizes of 1.9–10.8 nm at 250 °C, relatively larger expansions of 5–7% have been identified …”

Section: Resultsmentioning

confidence: 99%

“…It has become common to perform XAS experiments under reaction conditions . The work on supported Pd particles − has mainly focused on changes in structural order upon hydrogen exposure. Compared to fully metallic clusters, which are present in inert atmospheres, the particles in hydrogen atmospheres exhibited significantly reduced structural order and increased lattice constants, indicative of the formation of a palladium hydride phase .…”

Section: Introductionmentioning

confidence: 99%

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Comparative in Operando Studies in Heterogeneous Catalysis: Atomic and Electronic Structural Features in the Hydrogenation of Ethylene over Supported Pd and Pt Catalysts

Jung

Elsen

et al. 2015

ACS Catal.

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There exists an emerging opportunity, engendered by advances made in experimental methods of research, to address long-standing questions about the nature of the molecular mechanisms that are operative in important heterogeneous catalytic processes, as well as the nature of the complex atomic and electronic structural features that mediate them. Of particular interest in this regard is the understanding of the dynamical attributes of catalytic processesan understanding that might allow design principles to be applied to optimize the atomic and electronic structure of heterogeneous catalysts to sustain their performance in essentially any operating process condition. The current work explores these ideashighlighting capabilities of in operando methods of spectroscopic characterization as applied to an exemplary heterogeneous catalytic process, olefin hydrogenation. No heterogeneous catalytic process has been studied more intensively than olefin hydrogenation. The extensive literature available establishes important features by which metal catalysts activate and efficiently transform the bonding of the hydrogen and alkene reactants to generate a product alkane. Even so, many important mechanistic questions remain poorly understood due to the inherent multiscale complexity associated with heterogeneous catalytic transformations, as well as the paucity of methods suitable for their characterization in operando. The recent literature documents the development of new capabilities for characterization afforded by in situ and in operando methods. Of these, X-ray absorption spectroscopy (XAS) has become a particularly important technique for studying the mechanisms of catalytic reactions due to its capabilities for elucidating the nature of the atomic and electronic structural features of operating catalysts. Many important questions can now be addressed, in particular those that follow from the unique dynamical impacts and patterns of reactivity that occur in higher pressure (non-UHV) environments. In this Perspective, we examine important structure−property correlations for an exemplary model reactionethylene hydrogenationas elucidated in operando for two efficient catalyst materialsnanoscale Pd and Pt clusters supported on SiO 2 . The examined features include the following: the structural dynamics of the metal clusters and their sensitivity to the composition of the reactant feed; the role of hydrogen, and metal-and/ or support-bonded forms of adsorbates more generally, in forming intermediates and products; the influences of adsorbate bonding states (e.g., hydrogen) on reactivity; the role played by carbonaceous deposits (and the mechanisms of their formation); the quantitative nature of the atomistic features that exist within the structure−sensitivity correlations of this catalytic reaction; and mechanisms that mediate the sintering of catalysts operating in high-pressure ambient environment. Here we present a comparative overview of the hydrogenation of ethylene over ≈1 nm-sized Pd and Pt catalysts supported ...

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Comparative in Operando Studies in Heterogeneous Catalysis: Atomic and Electronic Structural Features in the Hydrogenation of Ethylene over Supported Pd and Pt Catalysts

Jung

Elsen

et al. 2015

ACS Catal.

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“…3 The detailed lattice structure of palladium nanoparticles and the formation of palladium hydride have been studied in detail using various techniques, including X-ray absorption spectroscopy (XAS). [11][12][13] Geometrical and electronic information of palladium nanoparticles and of palladium hydride can be obtained by performing XAS at the K and L edges. XAS at the K edge (∼24 350 eV) probes the transition of an electron from a 1s to a 5p orbital.…”

Section: Introductionmentioning

confidence: 99%

“…14 No contraction of particles was observed when palladium was supported on silica and carbon. 13 The formation of palladium hydrides can be determined from the lattice expansion, which is indicated by an increased interatomic distance. Expansion of the palladium lattice by 2.2 to 7% after hydride formation was observed on supported palladium particles.…”

Section: Introductionmentioning

confidence: 99%

Particle Size Effect of Hydride Formation and Surface Hydrogen Adsorption of Nanosized Palladium Catalysts: L₃ Edge vs K Edge X-ray Absorption Spectroscopy

2009

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The particle size effect on the formation of palladium hydride and on surface hydrogen adsorption was studied at room temperature using in situ X-ray absorption spectroscopy at the Pd K and L3 edges. Hydride formation was indirectly observed by lattice expansion in Pd K edge XANES spectra and by EXAFS analysis. Hydride formation was directly detected in the L3 edge spectra. A characteristic spectral feature caused by the formation of a Pd−H antibonding state showed strong particle size dependence. The L3 edge spectra were reproduced using full multiple scattering analysis and density of state calculations, and the contributions of bulk absorbed and surface hydrogen to the XANES spectra could be distinguished. The ratio of hydrogen on the surface versus that in the bulk increased with decreasing particle size, and smaller particles dissolved less hydrogen.

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“…Nanoparticles of Pd have been studied previously by X-ray absorption fine structure (XAFS) to compare their physical properties with those of bulk Pd. − Also, in situ XAFS of Pd catalysts has been studied during reduction of gas phase reactants − as well as in organic solvent . None of these studies, however, have characterized the particles in the presence of water or at the pressures and temperatures where the rates of the catalytic transformations are practicable.…”

Section: Introductionmentioning

confidence: 99%

State of Supported Pd during Catalysis in Water

et al. 2013

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The structure and chemical state of supported Pd nanoparticles in contact with H 2 in the aqueous phase have been explored by X-ray absorption spectroscopy to better understand their surface reactivity in polar condensed media. The Pd−Pd distances at substantial H 2 pressures indicate the presence of sorbed hydrogen and point to the presence of Pd hydrides, proving that such nanoparticles are hardly influenced by the presence of water. During the hydrogenation of the reactants (phenol, cyclohexanone, and cyclohexene), the Pd−Pd bond length decreased, indicating a drastically lower concentration of sorbed H compared to Pd in the absence of the reactants. This steady state concentration of sorbed hydrogen is established by all reactions involving H 2 , i.e., the sorption/desorption into the bulk, the adsorption at the surface, and the reaction with unsaturated reactants, but not by reaction with water. This demonstrates that neither the Pd particles nor the H/Pd ratio is influenced by water, but dynamically adapt to reaction conditions. Consistently, ab initio molecular dynamic simulations indicate that Pd−water interactions are relatively weak for Pd metal and that these interactions become even weaker, in the presence of H 2 and when hydrogen is incorporated into the metal particles.

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An exafs study of the influence of the metal particle size, nature of support, and adsorption of H2 and CO on the structure of palladium catalysts

Cited by 7 publications

References 2 publications

Comparative in Operando Studies in Heterogeneous Catalysis: Atomic and Electronic Structural Features in the Hydrogenation of Ethylene over Supported Pd and Pt Catalysts

Comparative in Operando Studies in Heterogeneous Catalysis: Atomic and Electronic Structural Features in the Hydrogenation of Ethylene over Supported Pd and Pt Catalysts

Particle Size Effect of Hydride Formation and Surface Hydrogen Adsorption of Nanosized Palladium Catalysts: L₃ Edge vs K Edge X-ray Absorption Spectroscopy

State of Supported Pd during Catalysis in Water

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An exafs study of the influence of the metal particle size, nature of support, and adsorption of H2 and CO on the structure of palladium catalysts

Cited by 7 publications

References 2 publications

Comparative in Operando Studies in Heterogeneous Catalysis: Atomic and Electronic Structural Features in the Hydrogenation of Ethylene over Supported Pd and Pt Catalysts

Comparative in Operando Studies in Heterogeneous Catalysis: Atomic and Electronic Structural Features in the Hydrogenation of Ethylene over Supported Pd and Pt Catalysts

Particle Size Effect of Hydride Formation and Surface Hydrogen Adsorption of Nanosized Palladium Catalysts: L3 Edge vs K Edge X-ray Absorption Spectroscopy

State of Supported Pd during Catalysis in Water

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Particle Size Effect of Hydride Formation and Surface Hydrogen Adsorption of Nanosized Palladium Catalysts: L₃ Edge vs K Edge X-ray Absorption Spectroscopy