Direct Observation of Surface Ethyl to Ethane Interconversion upon C2H4 Hydrogenation over Pt/Al2O3 Catalyst by Time-Resolved FT-IR Spectroscopy

Wasylenko, Walter; Frei, Heinz

doi:10.1021/jp053773o

Cited by 48 publications

(70 citation statements)

References 41 publications

(126 reference statements)

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“…23,33 The first hydrogenation step, converting π ethylene to a surface-bound ethyl intermediate, is generally accepted to be rate-determining, the ethyl coverage is very low under all conditions studied. 23,33 Other possible intermediates such as vinylidene, vinyl, or ethylidene have not been identified in surface science experiments and likely do not play an important mechanistic role in this reaction. 49 The second hydrogenation step, converting the ethyl intermediate to ethane, a formal reductive elimination of the ethyl group with adsorbed hydrogen, competes (generally) unfavorably with a reverse β-hydride elimination to ethylene, 53,54 as has been demonstrated by isotope exchange experiments (i.e., hydrogenation experiments with ethylene and deuterium), 11,13,22,43,55,56 in which essentially all possible deuterated ethane isotopomers were obtained.…”

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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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: ■ 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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“…4,5 The decay of the C 2 H 5 Pt species was found to exhibit the same temporal behavior as the rise of ethane, demonstrating directly the kinetic significance of the intermediate. The…”

Section: Introductionmentioning

confidence: 79%

Dynamics of Propane in Silica Mesopores Formed upon Propylene Hydrogenation over Pt Nanoparticles by Time-Resolved FT-IR Spectroscopy

Waslylenko¹,

Frei²

2007

J. Phys. Chem. C

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Propylene hydrogenation over Pt nanoparticles supported on mesoporous silica type SBA-15 was monitored by time-resolved FT-IR spectroscopy at 23 ms resolution using short propylene gas pulses that joined a continuous flow of hydrogen in N 2 (1 atm total pressure). Experiments were conducted in the temperature range 323 -413 K.Propane was formed within 100 milliseconds or faster. The CH stretching region revealed distinct bands for propane molecules emerging inside the nanoscale channels of the silica support. Spectral analysis gave the distribution of the propane product between support and surrounding gas phase as function of time. Kinetic analysis showed that the escape of propane molecules from the channels occurred within hundreds of milliseconds (3.1 + 0.4 s -1 at 383 K). A steady state distribution of propane between gas phase and mesoporous support is established as the product is swept from the catalyst zone by the continuous flow of hydrogen co-reactant. This is the first direct spectroscopic observation of emerging products of heterogeneous catalysis on nanoporous supports under reaction conditions.2

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“…under the con ditions for this application (100-200 °c), hydrogen can form a subsurface or bulk hydrides which play a role for the (undesired) full conversion of alkenes to alkanes. The hydrogena tion of the ethyl group seems to be the rate determining step [70] while several studies have observed the formation of ethylidyne species on Pd surfaces (*c-ch 3 ) [71]. Atomic hydrogen may form another σ bond with one of the two carbon atoms leading to an ethyl group on the surface.…”

Section: Kinetics and Reaction Mechanism Of Side Reactions (C 2 Species)mentioning

confidence: 99%

Methanation for Synthetic Natural Gas Production – Chemical Reaction Engineering Aspects

Schildhauer¹

2016

Synthetic Natural Gas From Coal, Dry Biomass, and Power‐to‐Gas Applications

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Direct Observation of Surface Ethyl to Ethane Interconversion upon C₂H₄ Hydrogenation over Pt/Al₂O₃ Catalyst by Time-Resolved FT-IR Spectroscopy

Abstract: Time-resolved FT-IR spectra of ethylene hydrogenation over alumina-supported Pt catalyst were recorded at 25 ms resolution in the temperature range 323 to 473 K using various H 2 flow rates (1 atm total gas pressure). Surface ethyl species (2870 and 1200 cm

Cited by 48 publications

References 41 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

Dynamics of Propane in Silica Mesopores Formed upon Propylene Hydrogenation over Pt Nanoparticles by Time-Resolved FT-IR Spectroscopy

Methanation for Synthetic Natural Gas Production – Chemical Reaction Engineering Aspects

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