Dissociative Adsorption Of Hydrogen Research Articles

Semihydrogenation of Acetylene on the (010) Surface of GaPd2: Ga Enrichment Improves Selectivity

Ab-initio density-functional calculations have been used to investigate the structure and stability of the (010) surfaces of the intermetallic compound GaPd2 and their activity and selectivity for the catalytic semihydrogenation of acetylene to ethylene. The calculations of the surface energies show that Ga-enrichment of the surface is energetically favored under Ga-rich preparation conditions. The bulk-terminated stoichiometric GaPd2(010) surface is catalytically active but does not exhibit the desired selectivity. The high Pd concentration in the surface leads to the formation of Pd3 triplets favoring a strong binding of ethylene and its further hydrogenation to ethyl. In contrast Ga-enriched GaPd2(010) surfaces provide an excellent selectivity for the formation of ethylene. Selectivity increases with increasing number of Ga atoms in the vicinity of the active Pd atoms. The atomistic scenarios for the dissociative adsorption of hydrogen, the diffusion of atomic hydrogen, and the hydrogenation reactions ...

The effects of hydrogen and ph on plasmon absorption of gold hydrosol. Electrochemical reactions on nanoelectrodes

A short-wavelength shift in the plasmon absorption band of 3-nm gold nanoparticles at their hydrosol saturation with hydrogen has been discovered and analyzed. It has been shown that dissociative adsorption of hydrogen occurs on a gold nanoparticle followed by the transfer of hydrogen in the form of a proton to a dispersion medium, with an electron remaining on the nanoparticle; i.e., a hydrogen nanoelectrode is realized. A linear increase in the magnitude of the experimentally observed shift in the plasmon resonance band with solution pH has been qualitatively explained.

Improved Effect of Anode-Additive PrBaInOx and Gd-doped BaCeO3 on the Electrochemical Performance of Solid Oxide Fuel Cells

PrBaInOx (PBI) and materials with related structures of perovskite were added to the anode of Solid Oxide Fuel Cells (SOFCs). The electrochemical performance of SOFCs improved by addition of PBI particles to the Ni/GDC anode in dry methane fuel. The effect of added PBI and materials with related structures of perovskite on the electrode characteristics was then investigated to determine the appropriate SOFC anode additive. Electrochemical measurements of Ni/GDC anodes with added PBI, PrInO3, BaCeO3 and Gd-doped BaCeO3 (BCG) suggest that BCG is the most effective anode additive for dry methane fuel. With wet H2 (1% H2O) fuel, the addition of BCG improved the electrochemical performance only of the Ni-free GDC anode, possibly due to the difference in hydrogen dissociative adsorption performance with and without Ni.

Dissociative Hydrogen Adsorption on the Hexagonal Mo2C Phase at High Coverage

Hydrogen adsorption on the primarily exposed (001), (100), (101), and (201) surfaces of the hexagonal Mo2C phase at different coverage has been investigated at the level of density functional theory and using ab initio thermodynamics. On the Mo-terminated (001) and (100) as well as mixed Mo/C-terminated (101) and (201) surfaces, dissociative H2 adsorption is favored both kinetically and thermodynamically. At high coverage, each surface can have several types of adsorption configurations coexisting, and these types are different from surface to surface. The stable coverage as a function of temperature and partial pressure provides useful information not only for surface science studies at ultrahigh vacuum condition but also for practical applications at high temperature and pressure in monitoring reactions. The differences in the adsorbed H atom numbers and energies of these surfaces indicate their different potential hydrotreating abilities. The relationship between surface stability and stable hydrogen c...

A ReaxFF Investigation of Hydride Formation in Palladium Nanoclusters via Monte Carlo and Molecular Dynamics Simulations

Palladium can readily dissociate and absorb hydrogen from the gas phase, making it applicable in hydrogen storage devices, separation membranes, and hydrogenation catalysts. To investigate hydrogen transport properties in Pd on the atomic scale, we derived a ReaxFF interaction potential for Pd/H from an extensive set of quantum data for both bulk and surface properties. Using this potential, we employed a recently developed hybrid grand canonical-Monte Carlo/molecular dynamics (GC-MC/MD) method to derive theoretical hydrogen absorption isotherms in Pd bulk crystals and nanoclusters for hydrogen pressures ranging from 10–1 atm to 10–14 atm, and at temperatures ranging from 300 to 500 K. Analysis of the equilibrated cluster structures reveals the contributing roles of surface, subsurface, and bulk regions during the size-dependent transition between the solid solution α phase and the hydride β phase. Additionally, MD simulations of the dissociative adsorption of hydrogen from the gas phase were conducted to assess size-dependent kinetics of hydride formation in Pd clusters. Hydrogen diffusion coefficients, apparent diffusion barriers, and pre-exponential factors were derived from MD simulations of hydrogen diffusion in bulk Pd. Both the thermodynamic results of the GC-MC/MD method and the kinetic results of the MD simulations are in agreement with experimental values reported in the literature, thus validating the Pd/H interaction potential, and demonstrating the capability of the GC–MC and MD methods for modeling the complex and dynamic phase behavior of hydrogen in Pd bulk and clusters.

Hydrogen adsorption on bimetallic PdAu(111) surface alloys: minimum adsorption ensemble, ligand and ensemble effects, and ensemble confinement.

The adsorption of hydrogen on structurally well defined PdAu-Pd(111) monolayer surface alloys was investigated in a combined experimental and theoretical study, aiming at a quantitative understanding of the adsorption and desorption properties of individual PdAu nanostructures. Combining the structural information obtained by high resolution scanning tunneling microscopy (STM), in particular on the abundance of specific adsorption ensembles at different Pd surface concentrations, with information on the adsorption properties derived from temperature programmed desorption (TPD) spectroscopy and high resolution electron energy loss spectroscopy (HREELS) provides conclusions on the minimum ensemble size for dissociative adsorption of hydrogen and on the adsorption energies on different sites active for adsorption. Density functional theory (DFT) based calculations give detailed insight into the physical effects underlying the observed adsorption behavior. Consequences of these findings for the understanding of hydrogen adsorption on bimetallic surfaces in general are discussed.

Dissociative Adsorption of Hydrogen on PdO(101) Studied by HRCLS and DFT

High-resolution core-level spectroscopy (HRCLS) and density functional theory (DFT) calculations have been used to investigate the adsorption and dissociation of hydrogen on a PdO(101) film grown on Pd(111). Energy-dependent measurements of the O 1s and Pd 3d5/2 binding energies enable identification of surface components that correspond to undercoordinated Pd and O atoms. HRCLS data obtained at 110 K, after hydrogen exposure at the same temperature, reveal hydrogen adsorption and formation of Pd-H and O-H groups. Adsorption at room temperature results instead in complete reduction of the oxide. The experimental results are supported by the DFT calculations of core-level shifts and barriers for water formation.

Environment-driven reactivity of H2 on PdRu surface alloys

The dissociative adsorption of molecular hydrogen on Pd(x)Ru(1-x)/Ru(0001) (0 ≤ x ≤ 1) has been investigated by means of He atom scattering, Density Functional Theory and quasi-classical trajectory calculations. Regardless of their surroundings, Pd atoms in the alloy are always less reactive than Ru ones. However, the reactivity of Ru atoms is enhanced by the presence of nearest neighbor Pd atoms. This environment-dependent reactivity of the Ru atoms in the alloy provides a sound explanation for the striking step-like dependence of the initial reactive sticking probability as a function of the Pd concentration observed in experiments. Moreover, we show that these environment-dependent effects on the reactivity of H2 on single atoms allow one to get around the usual constraint imposed by the Brønsted-Evans-Polanyi relationship between the reaction barrier and chemisorption energy.

Yb-Decorated Carbon Nanotubes As a Potential Capacity Hydrogen Storage Medium

We report a first-principles study, which demonstrates that a single Yb atom coated on a single-walled nanotube (SWNT), B atom doped CNT and N atom doped CNT binds up to six hydrogen molecules. At high Yb coverage we show that a SWNT can strongly adsorb up to 3.18 wt% hydrogen. Yb-4f electrons have no contribution on the adsorp-tion of hydrogen molecules in Yb doped CNT. The charge analysis results show that 4f electrons remain in Yb. These results promote our fundamental understanding of dissociative adsorption of hydrogen in RE atom doped carbon nano-structures.

Hydrogen Storage in Carbon Nanotubes Prepared by Using Copper Nanoparticles as Catalyst

carbon nanotubes were synthesized by pyroysis method using copper nanoparticles as catalyst. The structure, phase composition and hydrogen storage capacity were investigated by TEM, XRD spectra and Electrochemical System. The results show that the diameter of carbon nanotubes is 200-500nm, The P-C-T curve of adsorbing hydrogen of samples was measured in the pressure up to 12 MPa at room temperature. we show that a SWNT can strongly adsorb up to 8-wt% hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.

Dissociative Hydrogen Adsorption on Close-Packed Cobalt Nanoparticle Surfaces

The dissociative adsorption of hydrogen on cobalt is central to a number of catalytic reactions, yet to date there are relatively few studies examining this important process. Here we utilize Co nanoparticles grown on Cu(111), instead of the traditional planar Co single crystals, to study a more catalytically relevant form of Co. We present scanning tunneling microscopy images of different phases of H on the close-packed Co nanoparticle surfaces with a range of densities. Our data reveal a so-far unreported high coverage phase of H with a (1 × 1) structure and elucidate the importance of spillover from step edges in H adsorption. We also illustrate that, in contrast to the low density phases, the H-(1 × 1) structure can only be formed at an intermediate temperature, indicating that compression to this higher-density phase is activated. Density functional theory calculations yield energies for each of the H overlayer structures, as well as their preferred geometries. This work is the first to report on higher coverage (>0.75 ML) phases of H on Co, which are undoubtedly important in catalytic systems at elevated pressure. Finally, through the use of epitaxial Co nanoparticle growth on Cu(111), we illustrate the importance of step edges in H2 activation and the formation of dense H phases.

The (2 1 0) surface of intermetallic B20 compound GaPd as a selective hydrogenation catalyst: A DFT study

Recently, it has been demonstrated that intermetallic compounds composed of transition (Pd and Co) and simple (Ga and Al) metals used as catalysts provide excellent efficiency and selectivity for the hydrogenation of acetylene to ethylene. Motivated by experimental work on GaPd catalysts, we have performed a detailed density-functional study of the hydrogenation of acetylene catalyzed by the B20-type GaPd compound. We have identified the pseudo-fivefold (210) surface of the B20 structure as a possible catalytically active surface termination. The atomic structure of the (210) surface can be described by a triangle-rectangle tiling. An atomistic scenario has been constructed for the hydrogenation process catalyzed by this surface. We demonstrate that the active sites for the hydrogenation of acetylene to vinyl and further to ethylene are triangular arrangements of two Ga and one Pd atom atoms. Acetylene is bound to bridge sites formed by two Ga atoms. Vinyl formed in a first hydrogenation step is strongly attached to a Ga atom through its CH group, while the CH2 group shifts toward a neighboring Pd atom. In contrast, ethylene is bound only on top of the Pd atom most strongly protruding from the surface. The activation energies for all steps of the reaction (dissociative adsorption and diffusion of hydrogen, adsorption of all hydrocarbon species, hydrogenation of acetylene to vinyl, of vinyl to ethylene, and of ethylene to ethyl, desorption of ethylene) have been calculated. The activation energies for the rate-controlling steps of 60–70kJ/mol are comparable to those on other catalytically active compounds AlPd and Al13Co4 investigated in previous studies and also comparable or even lower than for a pure Pd catalyst. The desorption energy for ethylene of 45kJ/mol is at least by 14kJ/mol lower than the activation energy of ethylene to ethyl and provides thus excellent selectivity of GaPd. We show that the decisive factors for the activity and selectivity of the catalyst (corrugated surface with slightly protruding transition-metal atoms forming together with two neighboring Al/Ga atoms a triangular arrangement) are essentially the same on all investigated intermetallic compounds GaPd, AlPd, and Al13Co4.

Dissociative adsorption of hydrogen on the ZrB2(0001) surface

We have studied the dissociation of H2 on the ZrB2(0001) surface using density functional theory and reflection absorption infrared spectroscopy (RAIRS). Our results show that H2 readily dissociates on the Zr-terminated (0001) surface up to a H coverage of 1/2ML. Furthermore, we show that H is very mobile on the surface and that it desorbs between 545 and 625K. The calculated vibrational frequencies for the adsorbed H are in excellent agreement with our RAIRS measurements and with previously reported high resolution electron energy loss spectra.

On the formation of surface gallium hydride species in supported gallium catalysts

Molecular hydrogen is dissociatively adsorbed at elevated temperatures on Ga3+ surface sites of supported gallium catalysts. Both the amount of hydrogen absorbed by the catalysts and GaH vibration frequencies of surface gallium hydrides formed upon dissociative hydrogen adsorption depend on the nature of the support. The surface sites, active in the dissociative adsorption of hydrogen, most probably are Ga3+ cations bonded to the support surface.

Dissociative adsorption of H2 molecules on steric graphene surface: Ab initio MD study based on DFT

Recently, carbon materials have attracted considerable attention with their strong potential for hydrogen storage. In the present study, the possibility for dissociative adsorption of hydrogen on the surface of graphene is investigated by using ab initio molecular dynamics (MDs) based on density functional theory. The orientation of a H2 molecule with respect to a modeled graphene surface (perpendicular or parallel) is taken into account in this investigation, and the differences between results obtained with different values of the incident energy are discussed. The adsorption processes of hydrogen molecules are simulated by focusing on electron transfer between H and C atoms, in which dissociation and adsorption of H2 are found to be promoted above the steric graphene structure due to pronounced electron transfer at the impact point. The local steric structure forms sp3 hybridized molecular orbitals, which results in increased electron density and acts as a catalytic agent inducing cleavage of the H–H bond. In MD simulations, an excess incident energy of 6.00eV (579kJ/mol) is required to promote the reaction, although the activation energy is evaluated as 3.33eV (321kJ/mol) by static electronic structure computation. This result is obtained by taking both the motion of molecules as well as electron transfer into account and assuming that chemical reactions do not always progress along the ideal reaction pathway in actual systems.

Kinetic study of the partial hydrogenation of 1‐heptyne on tungsten oxide supported on alumina

AbstractBACKGROUND: Partial hydrogenation of alkynes have industrial and academic relevance on a large scale; industries such as petrochemical, pharmacology and agrochemical use these compounds as raw material. Typical commercial catalysts contains palladium. Finding an economic, active and selective catalyst for the production of alkenes via partial hydrogenation of alkynes is thus an important challenge. On the other hand, the literature on kinetic studies of partial hydrogenation of heavy alkynes is scarce. So the main objectives of this work were to prepare a cheaper catalyst based on low W loading, and study the kinetic of the partial hydrogenation of 1‐heptyne. A pseudo‐homogeneous and six heterogeneous kinetic models were analyzed. The catalyst was characterized by ICP, XPS, DRX, TPR and hydrogen chemisorption techniques.RESULTS: The characterization results indicate that only WOx species are present on the alumina surface. The WOx/Al2O3 catalyst was active and selective for producing 1‐heptene even at low reaction temperatures, the partial hydrogenation of 1‐heptyne proceeds via two irreversible reactions in parallel.CONCLUSION: The best fit of the experimental data was achieved with a heterogeneous Langmuir‐Hinshelwood‐Hougen‐Watson model in which the rate controlling step is the dissociative adsorption of hydrogen. The activation energy was estimated as EH2 = 34.8 kJ mol−1. Copyright © 2012 Society of Chemical Industry

Assessing the coupled heat and mass transport of hydrogen through a palladium membrane

We have formulated the coupled transport of heat and hydrogen through a palladium membrane, including the dissociative adsorption of hydrogen at the surface. This was done using the systematic approach of non-equilibrium thermodynamics. We show how this approach, which deviates from Sieverts’ law, makes is possible to calculate the direct impact that a temperature gradient, or a heat flux, has on the hydrogen flux. Vice versa, we show how the dissociative adsorption leads to heat sinks and sources at the surface.Using a set of transport coefficients estimated from experimental values available in the literature, calculations were performed. An enhancement of the hydrogen flux through the membrane with 10% and 25%, by transmembrane temperature differences of 24.8K and 65.6K, respectively, was predicted with a feed temperature of 673K. Similarly, a transmembrane temperature difference of −176.5K was observed to stop the hydrogen flux (Soret equilibrium). The calculations are done with estimated transport properties for the surfaces. The results show that an effort should be put into determination of these. Such experiments are discussed.

Hydrogen adsorption on and spillover from Au- and Cu-supported Pt3 and Pd3 clusters: a density functional study

Motivated by the use of electrodes modified at the nanoscale by supported metal species, we studied computationally how the reactivity changes in such a composite system compared to the reactivity of the individual systems, metal clusters and metal surfaces. Specifically, we examined hydrogen adsorption on and hydrogen spillover from Au- and Cu-supported Pt(3) and Pd(3) clusters, using a method based on Density Functional Theory. Two distinctive types of sites were found for the adsorption of atomic hydrogen: (i) on the supported clusters and (ii) at the cluster-substrate interfaces. The adsorption energy of hydrogen on the supported clusters is ∼20 kJ mol(-1) smaller when the cluster is supported by Cu instead of Au. In contrast, the substrate has no effect on hydrogen adsorbed at the cluster-substrate interfaces. Adsorbed Pt(3) and Pd(3) clusters locally modify the reactivity of the substrates as quantified by the reduced adsorption energy of hydrogen compared to the corresponding clean substrate. Hydrogen dissociative adsorption followed by spillover is thermodynamically and kinetically favored for clusters supported on a Cu surface, but not on Au. Moreover, spillover of hydrogen is more likely from metal-supported Pd than Pt clusters as revealed by barriers that are calculated 40-50 kJ mol(-1) lower in energy.

The electric field as a novel switch for uptake/release of hydrogen for storage in nitrogen doped graphene

Nitrogen-doped graphene was recently synthesized and was reported to be a catalyst for hydrogen dissociative adsorption under a perpendicular applied electric field (F). In this work, the diffusion of H atoms on N-doped graphene, in the presence and absence of an applied perpendicular electric field, is studied using density functional theory. We demonstrate that the applied field can significantly facilitate the binding of hydrogen molecules on N-doped graphene through dissociative adsorption and diffusion on the surface. By removing the applied field the absorbed H atoms can be released efficiently. Our theoretical calculation indicates that N-doped graphene is a promising hydrogen storage material with reversible hydrogen adsorption/desorption where the applied electric field can act as a switch for the uptake/release processes.

Hydrogen adsorption on electron-dopedC60monolayer on Cu(111) studied by He atom scattering

Hydrogen adsorption onto an electron-doped C${}_{60}$ monolayer on Cu(111) was examined at room temperature by means of highly surface-sensitive He atom scattering measurements. The electron-doped C${}_{60}$ was modeled utilizing the self doping of the C${}_{60}$ monolayer on the Cu(111) substrate. Hydrogen was found to adsorb randomly on the surface area of the electron-doped C${}_{60}$ monolayer, while the ordered structure of the C${}_{60}$ monolayer remained unchanged. The surface hydrogen layer desorbed completely below 420 K. Thermal desorption spectroscopy measurements suggested the dissociative adsorption of hydrogen. The driving mechanism to facilitate the adsorption in this system should be in agreement with recent theoretical predictions concerning the enhanced hydrogen storage ability of the doped carbon nanomaterials.