Adsorption Of Deuterium Research Articles

Adsorption of hydrogen and deuterium on potassium-promoted Pd(100) surfaces

The adsorption of H 2 and D 2 has been studied on clean and K-promoted Pd(100) surfaces using thermal desorption, work function changes, ultraviolet photoelectron and Auger spectroscopy. The potassium adlayer significantly lowers the sticking coefficient (from 0.6 to 0.06 at θ k = 0.2), and the uptake of hydrogen, but increases the desorption energy for H 2 desorption. Calculation showed that each potassium adatom blocks approximately 4–5 adsorption sites for H 2 adsorption. Atomization of hydrogen led to an increase of hydrogen uptake. The adsorption of potassium on the H-covered surface caused a significant decrease in the amount of hydrogen adsorbed on the surface (as indicated by less desorbing hydrogen below 500 K) and promoted the dissolution of H atoms into the bulk of Pd. The dissolved hydrogen was released only above 600–650 K. In the interpetation of the results the extended charge transfer from K-dosed Pd to the adsorbed H atoms and the direct interaction between adsorbed H and K adatoms are taken into account.

Reconstruction of Cu(100) by adsorption of atomic hydrogen

The adsorption of hydrogen and deuterium on a Cu(100) single crystal has been investigated as a function of coverage using an atomic hydrogen doser. It was found that the Cu(100) surface undergoes a reconstruction into the rather rare p4g or pgg structure. The reconstruction took place only at the very highest coverage and it was found to be followed by an adsorption site change for some of the hydrogen from a hollow site into a bridge bonded site. The thermal desorption spectra revealed a memory effect, suggesting a strong mass transport or modulation of the surface during the reconstruction.

Reconstruction of Cu(100) by adsorption of atomic hydrogen

Abstract The adsorption of hydrogen and deuterium on a Cu(100) single crystal has been investigated as a function of coverage using an atomic hydrogen doser. It was found that the Cu(100) surface undergoes a reconstruction into the rather rare p4g or pgg structure. The reconstruction took place only at the very highest coverage and it was found to be followed by an adsorption site change for some of the hydrogen from a hollow site into a bridge bonded site. The thermal desorption spectra revealed a memory effect, suggesting a strong mass transport or modulation of the surface during the reconstruction.

Ultra-thin cobalt films on Mo(110): overlayer growth and chemisorption of CO and D 2

The overlayer growth of cobalt on Mo(110) and the adsorption of CO and deuterium on Co/Mo(110) have been studied by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and temperature-programmed desorption (TPD). Co grows layer by layer on Mo(110) at a sample temperature of 115 K. Annealing multilayers of Co on Mo(110) to > 400 K results in the formation of three-dimensional (3D) Co clusters. The TPD spectra of Co from Mo(110) reveal two desorption peaks, β 1 and β 2, with activation energies of 82 and 85 kcal/mol, corresponding to desorption from 3D Co clusters and the first uniform Co overlayer, respectively. Submonolayer Co( < 0.75 ML, where 1 ML corresponds to the atomic density of the Co(0001) surface) is believed to form a pseudomorphic layer on Mo(110) upon annealing to 400 K. Co coverages from 0.75 to multilayers, annealed to 500 K, exhibit the following LEED patterns: a 9 × 2 structure, a hexagonal structure, and a 2 × 2 structure. The 9 × 2 and hexagonal structures are interpreted to correspond to a distorted lattice of Co(0001) and to 3D Co clusters on Mo(110), respectively. The TPD spectra of CO or D 2 on Co overlayers show desorption features with lower activation energies than the analogous desorption features from bulk Co(0001).

The role of surface conditions on fatigue behaviour of metal parts: Lieurade, H.-P. Surfaces Sept. 1989 27, (208), 70–71, 74, 77–78, 80 (in French)

Measurements of the permeation rate of deuterium in martensitic steel DIN 1.4914 (MANET) were performed by a gas permeation technique over the temperature range 560–740 K and for deuterium driving pressures in the range from 9 to 5 × 104 Pa. From these measurements, the surface constants for the adsorption (σ-κ1) and release (σ,κ2) of deuterium in MANET were determined. The experimental values of the surface constants σκ1 and σκ2 are well described by the following equations: σ k1= 7.66 × 10−6 exp (−55217/RT) (mol m−2 Pa−1 s−1), σκ2 = 2.59 × 10−5 exp (5781/RT) (mol−10 m4 s−1), where R = 8.314 J K−1 mol−1 and T is the temperature in Kelvin.

Deuterium adsorption on thin nickel films

Adsorption states arising upon interaction of deuterium with thin nickel films at 298 and 78 K were distinguished by simultaneous surface potential and pressure measurements. Rapid recording, sensitive and nondisturbing methods (static capacitor and ultrasensitive Pirani-type gauge) were applied. Negatively polarized β - adspecies are formed at 298 K, while at 78 K the β - state arising at low coverage is followed by the positively polarized β + state. The features of the β + state are described. The isotope effect is shown.

Adsorption and reaction of oxygen and deuterium on a Pd(110) surface, studied by Δφ and TDS

The co-adsorption of oxygen and deuterium at 100 K on a Pd(110) surface has been studied by measurements of the change in work function (Δφ) and by thermal desorption spectroscopy (TDS). When the surface with co-adsorbed species is heated, the adsorbates O and D react to form D 2O which desorbs from the surface at T > 200 K. The D 2O desorption peaks shift continuously to lower temperatures as the surface D coverage (θ D) increases. The maximum production of D 2O is estimated to be ∼ 0.26 ML (1 ML = 9.5 × 10 14 atoms cm −2), resulting from reaction in a layer containing 0.65 ML D and ∼ 0.3 ML O. The maximum work function increase caused by adsorption of D to saturation onto oxygen precovered Pd(110) decreases almost linearly with Δφ O of the oxygen precovered surface. On a surface with pre-adsorbed D however, the maximum Δφ increase contributed by oxygen adsorption decreases abruptly at Δφ D > 200 mV. This sharp change occurs at θ D > 1 ML and is believed to be associated with the development of the reconstructed (1 × 2) phase of D/Pd(110).

Weakly bound hydrogen state on thin iron films

Hydrogen and deuterium adsorption on thin iron films deposited under uhv conditions was studied over the pressure range 10 −10–10 −1 torr within the temperature interval 78 K – 298 K, measuring simultaneously surface potential and pressure. A rapidly recording (response time 1 ms) static capacitor system and ultrasensitive Pirani-type gauge were applied to avoid atomic hydrogen presence in the gas phase. The weakly adsorbed β − w state of the adsorbate following the strongly adsorbed β − s state was clearly distinguished. Isosteric heat of adsorption, differential entropy, spreading pressure and sticking probability for the β − w state are determined as a function of coverage. Isotope effect is demonstrated.

Fourier transform-infrared spectroscopic study of the adsorption of hydrogen on chromia and on some metal chromites

Adsorption of hydrogen and deuterium on samples of chromia and on nonstoichiometric zinc, cobalt, and manganese chromites (M/Cr atomic ratio 1:1; M = Zn, Co, Mn), previously activated in hydrogen and vacuum, was studied by means of Fourier transform-infrared spectroscopy. Parallel CO adsorption experiments indicate that all four catalysts are essentially in an oxide form after hydrogen adsorption. Only in the case of the cobalt compound are zerovalent centers observed. Terminal hydrides CrH are formed on chromia, whereas on the three chromites, both terminal and bridged hydride species, thought to be bonded to Zn 2+, Co 2+, and Mn 2+ centers, respectively, are observed. These assignments are based on the H(D) isotopic shift and on a comparison with the spectra of known hydride species of the same metals. The mechanism of formation of these adsorbed forms is briefly discussed.

Direct and precursor dynamics in dissociative hydrogen chemisorption on Ni(100)

We report evidence for the coexistence of direct and precursor dynamics in the dissociative chemisorption of H2 on Ni(l00). Hydrogen and deuterium uptakes on Ni(l00) were measured at various surface temperatures by following the secondary ion ratios, Ni2 H+/Ni+ and Ni2 D+/Ni+ , which are proportional to surface hydrogen and deuterium coverage on both clean and carbon-covered Ni(100). Between 100 and 200 K on clean Ni(l00), the initial sticking coefficient of hydrogen decreases, but only slightly, as the surface temperature increases. The decrease is more pronounced both in the presence of predosed carbon and for deuterium adsorption on Ni(100). This is interpreted as due to the involvement at low temperatures of a molecular precursor which mediates dissociative adsorption at low temperatures. The precursor probably involves surface defects and sites formed in the presence of carbon. In addition to the precursor channel, a direct dissociation channel also operates, and dominates for T≥200 K.

D2 on Pd(110): Surface and subsurface phases, absolute coverages, and interconversion

The adsorption of deuterium on Pd(110) has been studied by means of low‐energy electron diffraction, work function measurements (Δφ), thermal desorption spectroscopy, nuclear reaction analysis (NRA), and Rutherford backscattering (RBS). These measurements show that, upon D2 adsorption at low temperature, (2×1) and (1×2) phases are formed in sequence. The RBS data show that the (2×1) structure is unreconstructed, while the (1×2) is reconstructed, with an entire monolayer (ML) of Pd atoms displaced laterally from their bulklike locations by ≳0.01 nm. The NRA data demonstrate that depending on the method of preparation, the (2×1) phase can be associated with a total coverage of 1 or 1.5 ML, while the (1×2) phase can be produced with total coverages of 1.5 or 2 ML. The additional 0.5 ML, associated with the high coverage form of each phase, is due to subsurface adsorbed species.

Interaction of hydrogen with Ir(111) and Ir(110) surfaces

Hydrogen and deuterium adsorption on Ir(111) and Ir(110) surfaces is studied by the HREELS method at 170 and 300 K. The vibrations observed in the energy loss spectra at 560 cm −1 for Ir(111) and at 590 cm −1 for Ir(110) are assigned to symmetric stretching of the bond of hydrogen with three indium atoms, a threefold hollow site being proposed for adsorption at low temperatures on both surfaces. The differences in behaviour of hydrogen during adsorption on the two surfaces are interpreted on the basis of the faces under consideration. Different modes of the bond between the hydrogen atoms and the iridium surface at room temperature are discussed.

Adsorption of hydrogen on a stepped nickel surface

The adsorption of hydrogen and deuterium on a stepped nickel surface, Ni(510), has been studied using electron energy loss spectroscopy, EELS. At a surface temperature of ~100 K both dissociative and molecular chemisorption is found. For small doses hydrogen atoms adsorb in both hollow sites on the terraces and in low symmetry bridge sites at the steps with a preference for the step sites. For larger exposures, 0.5–0.9 L H 2, a dense layer of hydrogen atoms is formed on the terraces and the coverage increases at the steps where a second kind of step site gets occupied. Finally, for exposures larger than 0.9 L H 2, hydrogen molecules chemisorb at sites above the steps.

The adsorption and reaction of hydrogen and deuterium on a nickel/silica catalyst

The adsorption and reaction of hydrogen and deuterium on a nickel/silica catalyst

Adsorbate induced charge-exchange of low-energy He + scattered from a TiC(111) surface

The scattering of low-energy (300 eV) He + ions from a TiC(111) surface covered with oxygen, deuterium and sodium has been studied on the basis of neutralization of the ions. The intensity of surviving He + scattered from Ti for the deuterium (oxygen) saturated surface is reduced to 17% (less than 2%) of that for the clean surface mainly due to the Auger neutralization, while the neutralization of reionized He 0 appears to be less influenced by the existence of these adsorbates. The probability for the neutralization induced by deuterium adsorption is almost independent of the scattering trajectory. For the sodium adsorbed surface with a work function as small as about 2.8 eV, the He + intensity decreases to less than 20% of that for the oxidized surface with a work function as large as about 4.2 eV due to the resonance neutralization.

Direct observations of the deuterium-induced surface reconstruction of the Ni(110) plane.

The reconstruction of the Ni(110) plane induced by the adsorption of deuterium has been investigated in atomic detail with the field ion microscope. Small clusters of Ni atoms were observed to rearrange from a bulk-terminated structure to a ``missing-row'' structure upon exposure to ${10}^{\mathrm{\ensuremath{-}}8}$-Torr deuterium at 165--175 K. The observed structure is inconsistent with the ``paired-row'' structure deduced from low-energy electron diffraction and ion-scattering measurements.

Perturbations in the surface chemistry of hydrogen by nitrogen adatoms on platinum(110)-(1.times.2)

The kinetics of adsorption and desorption of deuterium have been studied on Pt(110)-(1x2) surfaces on which various fractional coverages of nitrogen adatoms are present. The nitrogen was adsorbed via the decomposition of ammonia at 400 K, at which temperature the initial probability of dissociative adsorption is approximately 4 x 10/sup -3/. Nitrogen selectively blocks the high-temperature ..beta../sub 2/-state of deuterium prior to poisoning the low-temperature ..beta../sub 1/-state. No evidence of a long range electronic perturbation of the surface by the nitrogen adatoms was found. The adsorption kinetics of deuterium on both clean and nitrogen-precovered Pt(110)-(1x2) surfaces were Langmuirian. In particular, adsorption into the ..beta../sub 2/-state was first order with respect to the fraction of vacant surface sites, and adsorption into the ..beta../sub 1/-state was second order in all cases. The modification of the desorption rate coefficients of deuterium on Py(110)-(1x2) by the nitrogen adatoms was measured quantitatively. Nitrogen modifies the preexponential factor and the activation energy of desorption of deuterium on Pt(110)-(1x2) by essentially rescaling the effective coverage of the deuterium. For the ..beta../sub 2/-state, the activation energy and the preexponential factor of the rate coefficient of deuterium desorption from both clean and nitrogen-precovered Pt(110)-(1x2) display a compensation effect. Themore » activation energy of desorption of nitrogen from Pt(110)-(1x2) was determined to be 24 kcal x mol/sup -1/ and relatively independent of coverage, whereas the preexponential factor decreases from approximately 5 x 10/sup -5/ cm/sup 2/ x s/sup -1/ at low coverages (theta/sub N/ less than or equal to 0.15) to approximately 5 x 10/sup -7/ cm/sup 2/ x s/sup -1/ at higher coverages (theta/sub N/ greater than or equal to 0.3).« less

The interaction of hydrogen with a rhodium (110) surface

The dissociative adsorption of hydrogen and deuterium on a Rh(110) surface was studied in UHV at 80 K by means of LEED, thermal desorption spectroscopy (TDS) and work function (Δ ϕ) measurements. We find atomic desorption in three different binding states α 1, α 2 and β having activation energies for desorption of ∼ 33, ∼ 53 and ∼ 90 kJ/mol, respectively. The initial sticking probability, s 0, is 0.97±0.10; the adsorption kinetics follows a precursor state model. The saturation coverage reaches the abnormally high value of 2 H atoms per Rh surface atom. Hydrogen forms a variety of ordered lattice gas phases, namely, a p(1×3) at θ H = 0.33, a p(×2) at θ H = 0.5, a 1×2−2H at θ H = 1.5 and a 1×1–2H at θ H = 2.0 with pronounced lateral interaction energies between the adsorbed H atoms. A layer relaxation or slight surface reconstruction induced by adsorbed H cannot be ruled out from our data.

Activated adsorption of deuterium on Ni(110): evidence for a high temperature desorption state

Cooling a clean Ni(110) sample in D 2 from T ≥ 350 K results in the appearance of a new high temperature peak ( β 3) centred at ∼ 435 K in the thermal desorption spectrum. The Ni surface is also reconstructed to the streak (St) phase. For exposures up to ∼ 10 −1 Pa s during slow cooldown, the β 3 state saturates at ∼ 0.06 monolayers (ML). It is not formed upon exposure at T ≤ 320 K even though the St phase may form under these conditions. The desorption of the ß 3 state occors without change in work function. Nuclear reaction analysis (NRA) has shown that the total coverage obtained on cooling from T ≥ 350 K to 170 K is 1.7±0.05 ML, significantly higher than obtained upon saturation at 170 K (1.5 ML). The ß 3 state probably arises from deuterium at sites just below the surface. The desorption is limited by activated migration to the surface at temperatures at which the equilibrium coverage would be very small. The ß 3 state might be associated with the final stages of removal of the St phase.

Heterolytic dissociation of hydrogen on high-temperature methanol synthesis catalysts

The heterolytic dissociation of hydrogen is thought to constitute the hydrogen-activation step in the mechanism of methanol synthesis. No data have been reported until now for the adsorption of hydrogen on the high-temperature methanol synthesis catalysts based on Zn/Cr mixed oxides, with a Zn/Cr atomic ratio higher than 0.5. In the present communication results of an IR study of the adsorption of hydrogen and deuterium on stoichiometric (Zn/Cr = 0.5) and nonstoichiometric zinc-rich spinels (Zn/Cr = 0.6 and 1.0) are reported. X-ray diffraction (XRD) analysis of such samples indicates that all samples are monophasic, showing only the presence of the spinel-type phases. Furthermore, these samples were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with an energy dispersive X-ray analyzer (EDX), and the presence of particles containing only zinc was not found. 30 references.