ADSORPTION OF HYDROGEN ON β-Ga2O3(100): A THEORETICAL STUDY

Gonzalez, Estela Andrea; Jasen, Paula Verónica; Luna, Carla Romina; Juan, Alfredo

doi:10.1142/s0218625x07009098

Cited by 8 publications

(3 citation statements)

References 25 publications

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“…A more likely explanation is that Ga-OH sites (and/or O vacancies), which are formed by the partial reduction of the HSA powder surface during annealing in H 2 , are necessary for the production of stable Ga-H sites. This is consistent with a suggestion based on recent theoretical work 71 for H adsorption on β-Ga 2 O 3 . It has also been suggested 72 in the case of γ-Al 2 O 3 HSA powders that H 2 dissociation, at least near room temperature, requires the presence of surface defects, believed to be Al sites with low coordination numbers.…”

Section: Surface Preparationsupporting

confidence: 93%

Infrared Spectroscopy and Surface Chemistry of β-Ga₂O₃ Nanoribbons

2007

Langmuir

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The structure and surface chemistry of crystalline beta-Ga2O3 nanoribbons (NRs), deposited in a thin layer on various metallic and dielectric substrates (mainly on Au), have been characterized using vibrational spectroscopy. The results have been analyzed with the aid of a previous ab initio theoretical model for the beta-Ga2O3 surface structure. Raman spectra and normal-incidence infrared (IR) transmission data show little if any difference from corresponding results for bulk single crystals. For a layer formed on a metallic substrate, IR reflection-absorption spectroscopy (IRRAS) shows longitudinal-optic (LO) modes that are red-shifted by approximately 37 cm-1 relative to those of a bulk crystal. Evidence is also seen for a bonding interaction at the Ga2O3/Au interface following heating in room air. Polarization-modulated IRRAS has been used to study the adsorption of pyridine under steady-state conditions in ambient pressures as high as approximately 5 Torr. The characteristic nu19b and nu8a modes of adsorbed pyridine exhibit little or no shift from the corresponding gas-phase values. This indicates that the surface is only weakly acidic, consistent with the theoretical prediction that singly unsaturated octahedral Ga sites are the only reactive cation sites on the NR surface. However, evidence for adsorption at defect sites is seen in the form of more strongly shifted modes that saturate in intensity at low pyridine coverage. The effect of H atoms, formed by thermal cracking of H2, has also been studied. No Ga-H or O-H bonds are observed on the pristine NR surface. This suggests that the previously reported presence of such species on Ga2O3 powders heated in H2 is a result of a partial reduction of the oxide surface. The heat of adsorption of atomic H on the pristine beta-Ga2O3(100) surface at 0 K is computed to be -1.79 eV per H at saturation (average of Ga-H and O-H sites), whereas a value of +0.45 eV per H is found for the dissociative adsorption of H2. This suggests that rapid recombinative desorption of H2 may limit the coverage of chemisorbed H on this surface.

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Section: Surface Preparationsupporting

confidence: 93%

Infrared Spectroscopy and Surface Chemistry of β-Ga₂O₃ Nanoribbons

2007

Langmuir

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“…β-Ga 2 O 3 (100) surface have been studied in previous studies. [56][57][58][59][60] Bermudez had studied the structure and properties of four different monoclinic β-Ga 2 O 3 surface, showing that (100) surface is the most stable surface. 61 In the present study, Ga 2 O 3 (100) surface is simulated by a unit cell (p(4×2), 12.37 Å × 11.79 Å) with an 20 Å vacuum region between slabs.…”

Section: Model and Computational Detailsmentioning

confidence: 99%

Periodic Density Functional Theory Study of Propane Dehydrogenation over Perfect Ga₂O₃(100) Surface

Liu

et al. 2008

J. Phys. Chem. C

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Propane dehydrogenation over perfect Ga 2 O 3 (100) was studied in detail by periodic density functional theory (DFT) calculations. It was found that the initial C-H bond activation mainly follows a radical mechanism that the two-coordinated surface oxygen site (O(2)) abstracts a hydrogen atom from propane with the formation of propyl radical and hydroxyl group (O(2)H). Physically adsorbed propyl radical can easily form propoxide or propylgallium intermediate. Subsequently, propene is formed by a second H abstraction from propyl, propoxide, or propylgallium by surface oxygen and Ga sites. H abstraction by O(2) site always has low energy barrier. However, it is difficult for the hydrogen atoms in the hydroxyl groups to leave the surface in the form of either H 2 or H 2 O. In addition, propene formed through H abstraction by oxygen site has high adsorption energy and is prone to further dehydrogenation or oligomerization, leading to fast deactivation of the catalyst. On the other hand, the formation of H 2 from GaH and hydroxyl group is much easier, although the formation of GaH has to overcome high energy barrier. Thus, there is a shift of rate-determining step for propane dehydrogenation: at the initial stage of the reaction, the rate-determining step is H abstraction by oxygen sites and then it shifts to H abstraction from various propyl sources by Ga sites to form gallium hydrides after the surface oxygen sites are consumed. Our results also indicate that dehydrogenation of propane mainly follows a direct dehydrogenation mechanism (DDH), whereas oxidative dehydrogenation (ODH) is energetically less feasible but cannot be ruled out in the presence of mild oxidant such as CO 2 .

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“…The lattice constants of 𝛽-Ga All calculations in this article were carried out with the Cambridge Serial Total Energy Package (CASTEP) code in the Materials Studio 2017 package. [13] The electronic states 3d 10 4s 2 4p 1 , 2s 2 2p 4 , and 3s 2 3p 2 are adopted as the valence states for Ga, O, and Si atoms, respectively. To obtain the accurate band-gap of 𝛽-Ga 2 O 3 , the GGA+ U method is adopted and the parameters of U d,Ga , and U p,O [14] are set to be 12.0 and 8.4 eV, respectively.…”

Section: Computational Detailsmentioning

confidence: 99%

First‐Principles Calculations of Electronic Structure and Optical Properties of Si‐Doped and Vacancy β‐Ga₂O₃

Liu

Gao

et al. 2021

Crystal Research and Technology

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The electronic structure and optical properties of Si-doped 𝜷-Ga 2 O 3 with vacancy are studied using the generalized gradient approximation plus the Hubbard term. The results show that the most easily formed are doping systems, followed by the doped with vacancy systems, and the vacancy systems. The conductivity of 𝜷-Ga 2 O 3 is enhanced significantly after being doped with Si, but its absorptivity decreased. The defect levels generated by the vacancy system can enhance the light absorption capability, especially O vacancy system. The doped with vacancy system may improve the conductivity and absorptivity in the visible range of the 𝜷-Ga 2 O 3 .

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ADSORPTION OF HYDROGEN ON β-Ga₂O₃(100): A THEORETICAL STUDY

Cited by 8 publications

References 25 publications

Infrared Spectroscopy and Surface Chemistry of β-Ga₂O₃ Nanoribbons

Infrared Spectroscopy and Surface Chemistry of β-Ga₂O₃ Nanoribbons

Periodic Density Functional Theory Study of Propane Dehydrogenation over Perfect Ga₂O₃(100) Surface

First‐Principles Calculations of Electronic Structure and Optical Properties of Si‐Doped and Vacancy β‐Ga₂O₃

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ADSORPTION OF HYDROGEN ON β-Ga2O3(100): A THEORETICAL STUDY

Cited by 8 publications

References 25 publications

Infrared Spectroscopy and Surface Chemistry of β-Ga2O3 Nanoribbons

Infrared Spectroscopy and Surface Chemistry of β-Ga2O3 Nanoribbons

Periodic Density Functional Theory Study of Propane Dehydrogenation over Perfect Ga2O3(100) Surface

First‐Principles Calculations of Electronic Structure and Optical Properties of Si‐Doped and Vacancy β‐Ga2O3

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Resources

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ADSORPTION OF HYDROGEN ON β-Ga₂O₃(100): A THEORETICAL STUDY

Infrared Spectroscopy and Surface Chemistry of β-Ga₂O₃ Nanoribbons

Infrared Spectroscopy and Surface Chemistry of β-Ga₂O₃ Nanoribbons

Periodic Density Functional Theory Study of Propane Dehydrogenation over Perfect Ga₂O₃(100) Surface

First‐Principles Calculations of Electronic Structure and Optical Properties of Si‐Doped and Vacancy β‐Ga₂O₃