Electrostatic adsorbate-adsorbate interactions: The poisoning and promotion of the molecular adsorption reaction

Lang, N. D.; Holloway, S.; Nørskov, Jens K.

doi:10.1016/0039-6028(85)90208-0

Cited by 390 publications

(124 citation statements)

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“…23,24 These sulfur atoms lower the surface activity by blocking the available adsorption/reaction sites on the surface due to sterical hindrance. 19,26,27 Such blocking has been found to affect both hydrogen and oxygen adatoms 27 which are used to regenerate the catalyst through either a reductive mechanism (formation and desorption of H 2 S) 12 or an oxidative mechanism (formation and desorption of SO 2 or SO 3 ). 28 The only study on a thermal oxidation reaction is an early temperature programmed desorption study, 29 which included isothermal experiments.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study

Gotterbarm

Luckas

Höfert

et al. 2012

The Journal of Chemical Physics

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We studied the reaction kinetics of sulfur oxidation on the Pd(100) surface by in situ high resolution x-ray photoelectron spectroscopy and ab initio density functional calculations. Isothermal oxidation experiments were performed between 400 and 500 K for small amounts (∼0.02 ML) of preadsorbed sulfur, with oxygen in large excess. The main stable reaction intermediate found on the surface is SO 4 , with SO 2 and SO 3 being only present in minor amounts. Density-functional calculations depict a reaction energy profile, which explains the sequential formation of SO 2 , SO 3 , and eventually SO 4 , also highlighting that the in-plane formation of SO from S and O adatoms is the rate limiting step. From the experiments we determined the activation energy of the rate limiting step to be 85 ± 6 kJ mol −1 by Arrhenius analysis, matching the calculated endothermicity of the SO formation.

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Section: Introductionmentioning

confidence: 99%

Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study

Gotterbarm

Luckas

Höfert

et al. 2012

The Journal of Chemical Physics

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“…The spectroscopic identification of the precursor state rationalizes many phenomena in gas-surface interactions [4][5][6][7][8] and underpins our fundamental understanding of the kinetics of elementary surface reactions. In heterogeneous catalytic processes, many different species or promoters exist on the surface that can influence each other through adsorbate-adsorbate interactions [11]. Effects of the coadsorbate interaction on desorption dynamics have, however, largely been unexplored and their role in the correlated chemical environment is presently still poorly understood [11][12][13].…”

mentioning

confidence: 99%

“…In heterogeneous catalytic processes, many different species or promoters exist on the surface that can influence each other through adsorbate-adsorbate interactions [11]. Effects of the coadsorbate interaction on desorption dynamics have, however, largely been unexplored and their role in the correlated chemical environment is presently still poorly understood [11][12][13].…”

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confidence: 99%

Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy andAb InitioSimulations

et al. 2015

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We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5σ and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.

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“…This result is surprising considering overwhelming evidence from FT-IR [Gracia 2002] and surface science studies [Holloway 1987, Lang 1985, Nørskov 1984 suggesting that the presence of Cl should actually destabilize the adsorption of CO due to electrostatic adsorbate-adsorbate interactions. However, because the deposition of Cl on the Pt surface is from the hydrodechlorination of TTCE, it can be speculated that the structure sensitivity of the reaction plays a role.…”

Section: Discussionmentioning

confidence: 97%

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Goodwin¹,

Colón-Mercado²,

Hongsirikarn³

et al. 2011

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EXECUTIVE SUMMARYThe main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. This project was carried out primarily at Clemson University and the Savannah River National Lab. Fuel cell investigations were done at SRNL while all investigations of the MEA components were carried out at Clemson. Meetings took place weekly at Clemson University and at SRNL with the respective project participants. Joint meetings between researchers at Clemson and SRNL took place quarterly, on average. In addition, frequent communications among project participants took place via e-mail and telephone discussions. On other occasions the researchers met with the technical staff of John Deere for discussions. At least one member of our team routinely participated in the DOE-Sponsored Joint Hydrogen Quality Task Force Meetings (usually conducted monthly).The nature and concentrations of impurities investigated and their impact on fuel cell performance and individual components are given in the table below. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion.Even though already well known as fuel cell poisons, the effects of CO and NH 3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization.New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H 2 -D 2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts.Using a combination of standard catalyst characterization techniques, a structure sensitive catalytic reaction technique (cyclopropane hydrogenolysis), and reaction and transport modeling led to the finding that in the catalyst layer (essentially Nafion/Pt/C) the following best describes the structure. Pt is highly dispersed on the C support, but primarily in the meso-and macropores. The Nafion (ca. 30 wt%) resides primarily on the external surface of the C support where it blocks significant numbers ...

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Electrostatic adsorbate-adsorbate interactions: The poisoning and promotion of the molecular adsorption reaction

Cited by 390 publications

References 38 publications

Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study

Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study

Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy andAb InitioSimulations

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

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