Hydrogen on Cobalt: The Effects of Carbon Monoxide and Sulphur Additives on the D2/Co(0001) System

Habermehl-Cwirzen, Karin; Kauraala, K.; Lahtinen, Jouko

doi:10.1238/physica.topical.108a00077

Cited by 35 publications

(71 citation statements)

References 2 publications

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“…This dose measurement also does not depend significantly on the hydrogen pressure: experiments were repeated with hydrogen pressure in the 10 −10 and 10 −9 Torr range and the total dose at which out-of-plane magnetic contrast vanishes agreed within 10%. These observations are consistent with the results from prior thermal programmed desorption studies (TPD [30][31][32], reporting that hydrogen adsorbs as atomic hydrogen on Co in a nonactivated reaction with the reported desorption energy of H/Co in the range of 0.85-1.0 eV/atom. 31 Assuming a constant sticking coefficient of 0.5 up to coverages of 0.5 ML, as reported in Ref.…”

Section: A Experimental Resultssupporting

confidence: 91%

Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)

et al. 2012

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Imaging the change in the magnetization vector in real time by spin-polarized low-energy electron microscopy, we observed a hydrogen-induced, reversible spin-reorientation transition in a cobalt bilayer on Ru(0001). Initially, hydrogen sorption reduces the size of out-of-plane magnetic domains and leads to the formation of a magnetic stripe domain pattern, which can be understood as a consequence of reducing the out-of-plane magnetic anisotropy. Further hydrogen sorption induces a transition to an in-plane easy axis. Desorbing the hydrogen by heating the film to 400 K recovers the original out-of-plane magnetization. By means of ab initio calculations we determine that the origin of the transition is the local effect of the hybridization of the hydrogen orbital and the orbitals of the Co atoms bonded to the absorbed hydrogen.

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Section: A Experimental Resultssupporting

confidence: 91%

Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)

et al. 2012

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“…[47] From Co (1), hydrogen desorbs with a maximum at % 330 K in the temperature interval from 250 to 450 K during methanol decomposition (Figure 3). This peak temperature is quite comparable to the value of 350 K observed in the TPD spectra after deuterium adsorption [48] as well Figure 2. Integral intensities of the TPD spectra in Figure 1 plotted against the amount of Pd in the particle system (0 % corresponds to monometallic Co, 100 % to monometallic Pd).…”

Section: Resultssupporting

confidence: 85%

UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

et al. 2008

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Bimetallic nanoparticles often turn out to be superior to the corresponding monometallic systems with respect to their catalytic properties. To study such effects for the methanol decomposition reaction, model catalysts were prepared by physical vapor deposition of Pd and Co under ultrahigh-vacuum (UHV) conditions. Monometallic Pd and Co particles as well as CoPd core-shell particles were generated on an epitaxial alumina film grown on NiAl(110). The interaction with methanol is examined by temperature-programmed desorption of methanol and carbon monoxide and by X-ray photoelectron spectroscopy. The decomposition of methanol proceeds in two reaction pathways independent of the particle composition: complete dehydrogenation towards carbon monoxide and hydrogen, and C--O bond scission yielding carbon deposits. Pd is the most active material studied here. The relative importance of the two channels varies for the different particle systems: on Pd dehydrogenation is preferred, whereas the C--O bond cleavage is more pronounced on Co. The bimetallic clusters show a moderate performance for both pathways. Carbon deposition poisons the model catalysts by blocking the adsorption sites for methoxide, which is the first intermediate product during methanol decomposition. In particular on Co, large amounts of carbon deposits can also be caused by dissociation of the final product of the dehydrogenation pathway, carbon monoxide. A comparison with the results of methanol decomposition on Co, Pd, and CoPd catalysts in continuous-flow reactors demonstrates that the findings of the present UHV study are relevant for catalytic performance under high-pressure conditions.

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“…For our 2H-(2 × 2) structure, the coverage is 0.5 ML, which corresponds well to the literature value for θ obtained by temperature programmed desorption, as well as the reported LEED results. 3,5 Additionally, our DFT results indicate that the H-(2 × 2) structure is much less favorable with respect to the 2H-(2 × 2) and suggest that the H-(2 × 2) (θ = 0.25 ML) would thermodynamically prefer to rearrange into regions of the 2H-(2 × 2) (θ = 0.5 ML) and bare Co (θ = 0 ML).…”

Section: ■ Results and Discussionmentioning

confidence: 73%

Dissociative Hydrogen Adsorption on Close-Packed Cobalt Nanoparticle Surfaces

Lewis

Murphy

et al. 2012

J. Phys. Chem. C

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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 H 2 activation and the formation of dense H phases.

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Hydrogen on Cobalt: The Effects of Carbon Monoxide and Sulphur Additives on the D2/Co(0001) System

Cited by 35 publications

References 2 publications

Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)

Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)

UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

Dissociative Hydrogen Adsorption on Close-Packed Cobalt Nanoparticle Surfaces

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