Interaction of hydrogen with solid surfaces

Christmann, K.

doi:10.1016/0167-5729(88)90009-x

Cited by 1,065 publications

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“…Nevertheless, there is a general consensus that the surface potential of β-PdH in equilibrium with H 2(g) is positive with respect to the work function of Pd metal and that the work function of β-PdH in equilibrium with H 2(g) is increased significantly with respect to that of Pd metal and is a consequence of lowering of the Fermi level and a positively polarized hydrogen species adsorbed on the surface of β-PdH. 25,29,[31][32][33][34]35 There is one other piece of evidence the H ads on Pd is positively charged. At 78 K and a hydrogen partial pressure that created a [H abs ]/[Pd] > 0.6, which is indicative of β-PdH, the surface potential is raised by approximately 1.3 V relative to that of Pd metal.…”

Section: Appendix C the Presence Of H Ads And H Ads + On The Surface mentioning

confidence: 99%

“…Dus' et al repeated the measurements of Conrad et al mostly at a temperature of 78 K and extended the tests to higher values of equilibrium partial pressure of hydrogen. [32][33][34] The experiments of Dus' et al were conducted on thin films (≈100 nm thick) of Pd. At low equilibrium partial pressures, which corresponded to hydrogen adsorbed on metallic Pd, the work function of palladium was increased in agreement with the higher temperature results of Conrad et al Once the equilibrium partial pressure of hydrogen was raised above a critical value further increases in partial pressure decreased the work function, indicative of the adsorption of positively charged hydrogen.…”

Section: Appendix C the Presence Of H Ads And H Ads + On The Surface mentioning

confidence: 99%

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Palladium Hydride as a Reference Electrode in Aprotic Solutions

Patrick

Chakravarti

Devine

2015

J. Electrochem. Soc.

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The results of a variety of electrochemical tests indicate palladium hydride (β-PdH) functions as a thermodynamic reference electrode in three aprotic solutions containing H 2(g) and solvents of dichloromethane, dimethylsulfoxide, and acetonitrile. For enhanced electrical conductivity all solutions contained 0.2 M of an ionic liquid, 1-methyl-3-butyl imidazolium tetrafluoroborate. As is required of all thermodynamic reference electrodes (i) the potential of β-PdH was stable, (ii) its small amplitude anodic and cathodic polarization were reversible, and (iii) it exhibited Nernstian behavior assuming that the hydrogen cation activity is controlled by the concentration of adsorbed hydrogen, which is set by the partial pressure of H 2(g) . © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0421603jes] All rights reserved.Manuscript submitted October 30, 2015; revised manuscript received December 8, 2015. Published December 17, 2015 Palladium hydride (PdH) has long been used as a redox system for measurement of pH, and as a titration electrode in nonaqueous solvents.1 The present investigation of PdH as a reference electrode in aprotic solutions arose from an interest in applying electrochemical techniques to assess the corrosivity of crude oil. Specifically, the current study was an offshoot of our efforts to use cyclic voltammetry of platinum in crude oil as a means for identifying the presence and concentrations of redox active corrosive species, such as naphthenic acids, which contribute significantly to the corrosion of steels in crude oil.At present, TAN (Total Acid Number) is employed to estimate the corrosiveness of a crude oil. TAN is the number of mg of potassium hydroxide required to neutralize the acids present in a 1 g sample of crude.2 However, it has been known for some time that there is considerable scatter in plots of low and intermediate values of TAN versus crudes' corrosiveness.3,4 For this reason, we have investigated the possibility of employing electrochemical techniques to characterize the corrosivity of an unknown crude.There are two major obstacles preventing the use of electrochemical techniques to assess the corrosivity of crudes. The first is the high electrical resistivity of crude oil. In a separate study we have addressed the resistivity issue by a combination of the use of ultramicroelectrodes (UME) and the addition of a supporting electrolyte, which does not itself affect the solution's corrosivity. 5 Many virgin crude oils have electrical resistivities on the order of 1 × 10 8 ohm•cm, which, although it is a high value, is nevertheless sufficiently low to permit electrochemical testing by employing UMEs without the need for a supporting electrolyte. However, the main concern over a crude's corrosivity relates to co...

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Section: Appendix C the Presence Of H Ads And H Ads + On The Surface mentioning

confidence: 99%

Section: Appendix C the Presence Of H Ads And H Ads + On The Surface mentioning

confidence: 99%

Palladium Hydride as a Reference Electrode in Aprotic Solutions

Patrick

Chakravarti

Devine

2015

J. Electrochem. Soc.

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“…surface atoms (see ref. [10] and references therein), in this paper the so-called "dangling bonds" on…”

Section: General Considerations Concerning the Adsorp-mentioning

confidence: 99%

“…The / /~/ / additional evidence exists (see ref. [7] and refer-/// // /// ,'-S1 2 ences therein) that the enthalpy should indeed be 10 …”

Section: -4 S1hmentioning

confidence: 99%

A theoretical study of adsorption equilibria in silicon CVD

Gardeniers

Giling

Jong

et al. 1990

Journal of Crystal Growth

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As part of a theoretical study of adsorption processes in the chemical vapour deposition of silicon, thermochemical data are derived for the adsorption of Si-H species on the Si(111) and the dimer-reconstructed Si(001)-(2 xl) surfaces. Essential contributions to the heats of adsorption appear to be electron pairing and two-and three-body interactions. It is shown that when the bond energies are defined in this way, also a consistent description of the bonds in silicon hydrides is provided. This demonstrates that with reasonable confidence the method can be applied to the adsorption process itself. Data are derived for species which may form one, two or even four bonds with the surface. It is assumed that on the (111) surface adsorbates bind on the "dangling bonds" which are present on this surface in a broken bond model. It is demonstrated that on the dimer reconstructed Si(001)-(2 xl) surface, adsorbates will either bind on the surface atoms with one or two bonds, without the breaking of the dimer bonds, or, if the species have the possibility to form two or four bonds with the surface atoms, may become inserted into the dimer bonds. With the aid of the derived thermochemical data for adsorption and the Langmuir isotherm or modifications thereof, the coverage of the Si(111) and the dimer reconstructed Si(001)-(2X1) surfaces with species from the Si-H system is calculated. It is found that the equilibrium surface coverages of the Si(111) and the Si(001)-(2 xl) surfaces are very similar: the hydrogen coverage is high at all temperatures, while at low supersaturation the coverage with growth species is very low on both surfaces.

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“…The adsorption of hydrogen on ruthenium at low pressures has been a subject of considerable research [42]. while several higher pressure studies have been conducted by our research group [43][44][45][46][47][48][49][50][51][52].…”

Section: Adsorption Of Hydrogenmentioning

confidence: 99%

A Kinetic Study on the Adsorption and Reaction of Hydrogen over Silica-Supported Ruthenium and Silver–Ruthenium Catalysts during the Hydrogenation of Carbon Monoxide

VanderWiel

Pruski

King

1999

Journal of Catalysis

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kinetic study on the adsorption and reaction of hydrogen over silica-supported ruthenium and silverruthenium catalysts during the hydrogenation of carbon monoxide " (1998) Table 2. Summar\' of kinetic parameters for CO hydrogenation over Ru/SiO; 40 Table 3. Summar\-of kinetic parameters for CO hydrogenation over Ag-Ru/Si02 50 Table 4. Comparison of kinetic parameters for methanation over supported Ru 55 Table 5. Rate decreases during CO hydrogenation upon addition of Ag to Ru 57 catalysts Table 6. Experimental design 83 Table 7. Statistical analysis of Ru/Si02 rate data 85 Table 8. Statistical analysis of Ag-Ru/SiO^ rate data 86. RESEARCH OBJECTIVESAlthough the cataKtic hydrogenation of carbon monoxide has been a subject of considerable investigation for many years, its increasing economical attractiveness as an industrial source of hydrocarbons has recently led to a search for more active and selectiv e catalysts. A fundamental problem in the development of such catalysts is an incomplete knowledge of the operative surface processes, due in large part to the inability to accurately measure surface concentrations of reactant species during reaction. Specifically, the concentration of surface hydrogen proves difficult to estimate using normally revealing techniques such as transient isotopic e.xchange due to kinetic isotope effects. Knowledge of such concentrations is essential to the determination of the mechanisms of adsorption and reaction, since many kinetic parameters are concentration dependent.It is the aim of this research to investigate the mechanism and kinetics of the adsorption and reaction of hydrogen on silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide. The specific activity of ruthenium in Group IB-ruthenium bimetallic catalysts is known to decrease dramaticalh' upon addition of the Group IB metal, even though these metals do not directly adsorb or react with hydrogen or carbon monoxide. Since silver is known to selectively occupy low-coordination sites in silver-ruthenium bimetallic systems, it can be used as a tool to block these sites from adsorption and reaction. In this way. any differences between the kinetics of processes occurring at these sites can be resolved. The mechanism of this synergistic effect will be elucidated in terms of a "portal site mediated adsorption" model. Previous work by our group has proposed that hydrogen adsorption occurs via a mechanism where lowcoordination "portal" sites on the catalyst serve as locations for rapid, dissociative adsorption of hydrogen to supply the surface with hydrogen for reaction with carbon monoxide.By preadsorbing carbon monoxide onto the surface of ruthenium and silver-ruthenium catalysts, the kinetics of hydrogen adsorption and reaction can be monitored upon exposure of this surface to ambient hydrogen gas. This is accomplished by conducting identical experiments on two separate systems. First, the formation of methane is monitored using mass spectroscopy, and specific reaction rates a...

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Interaction of hydrogen with solid surfaces

Cited by 1,065 publications

References 482 publications

Palladium Hydride as a Reference Electrode in Aprotic Solutions

Palladium Hydride as a Reference Electrode in Aprotic Solutions

A theoretical study of adsorption equilibria in silicon CVD

A Kinetic Study on the Adsorption and Reaction of Hydrogen over Silica-Supported Ruthenium and Silver–Ruthenium Catalysts during the Hydrogenation of Carbon Monoxide

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