Scaling reducibility of metal oxides

Helali, Zeineb; Jedidi, Abdesslem; Syzgantseva, Olga A.; Calatayud, Mònica; Minot, Christian

doi:10.1007/s00214-017-2130-y

Cited by 71 publications

(103 citation statements)

References 90 publications

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“…> 5 eV ( Table 3). The stability of F-centers has also been observed in other poorly reducible oxides 71 , and is associated to a high coordination stabilized by electrostatic interaction with neighboring cations. Two main effects account for the value of the formation energy of oxygen vacancy.…”

Section: Bulkmentioning

confidence: 74%

H2 Dissociation and Oxygen Vacancy Formation on Ce2O3 Surfaces

Matz

Calatayud

2019

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H 2 dissociation on ceria (CeO 2) has attracted much attention in the last years because of its potential application in catalysis for hydrogenation reactions, as well as for the stabilization of hydride bulk and surface species. The ability of ceria to split hydrogen is strongly dependent on the surface morphology. However, to the best of our knowledge, the reactivity of the cerium sesquioxide Ce 2 O 3 Atype (hexagonal structure with space group 3 1) has not been previously addressed. In the present study, we investigate (i) the formation of oxygen vacancies in ACe 2 O 3 bulk and (ii) the effect of the surface topology in the H 2 dissociation and in the oxygen vacancy formation for the four most stable surfaces of ACe 2 O 3 : (0001), (01-11), (11-20) and (11-21). Our results indicate a significant decrease of the energetic barrier for the hydrogen dissociation compared to stoichiometric CeO 2 , with an activation energy of ~0.1 eV. Interestingly, Ce 2 O 3 surfaces lead to a heterolytic product with hydride species more stable than the homolytic product, which is the opposite behavior found in CeO 2. These results suggest a better performance of Ce 2 O 3 than CeO 2 for H 2 dissociation and provide insight in the nature of hydride-Ce 2 O 3 interfaces that could be important intermediates in the formation of CeH x phases from cerium oxide.

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Section: Bulkmentioning

confidence: 74%

H2 Dissociation and Oxygen Vacancy Formation on Ce2O3 Surfaces

Matz

Calatayud

2019

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“…18 β-Ga2O3 was found to be nonreducible via DFT. 19 Therefore, it is most likely that H2 follows heterolytic dissociation as shown in Fig. 1a.…”

Section: Imentioning

confidence: 99%

Chemical manipulation of hydrogen induced high p-type and n-type conductivity in Ga2O3

Islam

Liedke

Winarski

et al. 2020

Sci Rep

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Advancement of optoelectronic and high-power devices is tied to the development of wide band gap materials with excellent transport properties. However, bipolar doping (n-type and p-type doping) and realizing high carrier density while maintaining good mobility have been big challenges in wide band gap materials. Here P-type and n-type conductivity was introduced in β-Ga2O3, an ultra-wide band gap oxide, by controlling hydrogen incorporation in the lattice without further doping. Hydrogen induced a 9-order of magnitude increase of n-type conductivity with donor ionization energy of 20 meV and resistivity of 10 -4 Ω.cm. The conductivity was switched to p-type with acceptor ionization energy of 42 meV by altering hydrogen incorporation in the lattice. Density functional theory calculations were used to examine hydrogen location in the Ga2O3 lattice and identified a new donor type as the source of this remarkable n-type conductivity. Positron annihilation spectroscopy confirmed this finding and the interpretation of the results. This work illustrates a new approach that allows a tunable and reversible way of modifying the conductivity of semiconductors and it is expected to have profound implications on semiconductor field. At the same time it demonstrates for the first time p-type and remarkable n-type conductivity in Ga2O3 which should usher in the development of Ga2O3 devices and advance optoelectronics and high-power devices.

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“…The properties of the energetically favorable vanadium sites (in position T2 for V-OH, T2, T3 for V=O and T3 for V(=O)(-OH)) described above, present in the vanadium-substituted BEA zeolite, can be compared with the active centers present on the (010) surface of the most known vanadium catalyst-V 2 O 5 (see Table 5). The electronic structure of V 2 O 5 was a subject of several papers, where the cluster and periodic models and theory on various theory levels was used [23][24][25][26][27]29]. In here, we report the cluster calculations for the (010) V 2 O 5 surface using the V 20 O 62 H 22 cluster model-see Figure 9a.…”

Section: Comparison With V 2 Omentioning

confidence: 99%

“…Theoretical studies of V 2 O 5 reported in the literature aim at characterization of the bulk oxide and its surfaces and employ both cluster and periodic models [23][24][25][26]. Activity of V 2 O 5 in oxidation reactions prompted the intensive studies in its reducibility, formation of vacancies, and the re-oxidation [23,[27][28][29]. Vanadium pentoxide is a crystalline solid built of [VO 6 ] distorted octahedra, in which V-O bonds have different lengths: one of 1.58 Å, one of 1.78 Å, two of 1.89 Å, one of 2.02 Å, and one long bond of 2.78 Å.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Catalytic Properties of Vanadium Centers Introduced into BEA Zeolite and Present on (010) V2O5 Surface–DFT Studies

et al. 2020

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Vanadium-based catalysts, in which vanadium is present either as bulk V2O5 or as isolated species, are active in numerous oxidation reactions. In the present study, vanadium speciation and the possibility of its introduction in various forms (V=O, V–OH, V(=O)(–OH)) into the structurally different crystallographic positions in BEA zeolite was considered by means of Density Functional Theory (DFT). Out of nine nonequivalent positions, T2 and T3 positions are the most preferred. The former may accommodate V=O or V–OH, the latter V–OH or V(=O)(–OH). The structural and electronic properties of all possible centers present in the BEA zeolite are then compared with the characteristics of the same species on the most abundant (010) V2O5 surface. It is demonstrated that they exhibit higher nucleophilic character when introduced into the zeolite, and thus, may be more relevant for catalysis.

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Scaling reducibility of metal oxides

Cited by 71 publications

References 90 publications

H2 Dissociation and Oxygen Vacancy Formation on Ce2O3 Surfaces

H2 Dissociation and Oxygen Vacancy Formation on Ce2O3 Surfaces

Chemical manipulation of hydrogen induced high p-type and n-type conductivity in Ga2O3

Comparison of Catalytic Properties of Vanadium Centers Introduced into BEA Zeolite and Present on (010) V2O5 Surface–DFT Studies

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