Koexistente phasen vom FeSi-Typ in den mischungen Ni-Pd-Ga und Ni-Pt-Ga

doi:10.1016/0022-5088(75)90021-1

Journal of the Less Common Metals

Volume 42, Issue 1, August 1975, Pages 69-76

https://doi.org/10.1016/0022-5088(75)90021-1 Get rights and content

Zusammenfassung

Die Phasen Ni_mPd_50−mGa₅₀ und Ni_mPt_50−mGa₅₀ (m = 0…30) ändern in ihrem linear erschreckten Homogenitätsbereich weder die Valenzelektronenkonzentration noch die Konzentration der äusseren Rumpfelektronen, sondern nur die Konzentration der inneren Rumpfelektronen. Bei niedrigen Pd-bzw. Pt-Gehalten und bei Temperaturen unter 700 °C bestehen die Legierungen aus zwei Phasen verschiedener Zusammensetzung aber gleicher Kristallstruktur vom FeSi-Typ. Die von den Randphasen getrennten Phasen können Ni₃PdGa₄ bzw. Ni₃PtGa₄ genannt werden. In den koexistenten Phasen kann man für die Kommensurabilität der Rumpfelektronen korrelation zur Struktur einen kleinen aber charakteristischen Unterschied annehmen.

Abstract

Neither the valence electron concentration nor the concentration of the outer core electrons in the phases Ni_mPd_50−mGa₅₀ and Ni_mPt_50−mGa₅₀ (m = 0…30) change over their linearly extended homogeneity ranges, only the concentration of the inner core electrons. At lower Pd or Pt contents and at temperatures below 700 °C the alloys consist of two phases of different composition but with the same FeSi-type crystal structure. The phases separated from these marginal phases may be formulated as Ni₃PdGa₄ and Ni₃PtGa₄, respectively. In the coexistent phases it may be assumed that the commensurability of the core electron correlation to the crystal structure exhibits a small but characteristic difference.

Literatur (9)

K Khalaff et al.
J. Less-Common Met.
(1974)
G Phragmén
Jernkontorets Ann.
(1923)
F Wever et al.
Z. Kristallogr. Mineral.
(1930)
L Pauling et al.
Acta Crystallogr.
(1948)

There are more references available in the full text version of this article.

Cited by (26)

The role of Ga in the acetylene adsorption on PdGa intermetallic
2018, Applied Surface Science
Citation Excerpt :
An equilibrium lattice constant of 4.899 Å is used, as we obtained with a converged mesh of 7 × 7 × 7. This lattice constant agrees well with the experimental of 4.909 Å [48–50]. In order to understand C2Hx-PdGa interactions and bonding we used the concepts of Density of States (DOS) [53,54] and Bond Order (BO) as implemented in the DDEC6 method [55–57].
We performed density functional calculation of the acetylene hydrogenation reaction on the PdGa(110) surface. The reaction C₂H₂+H₂ → C₂H₄ is modeled and understood in terms of chemical bonding change. The evolution of electronic structure and electron density plot also shed more light on the role of Pd, Ga and C₂H₂ during the hydrogenation reactions. This new way of looking at a particular chemical reaction includes the changes in bond order in the different reaction steps. As mentioned before the role of Ga is revealed as a part of the active site and not a single spacer.
CO<inf>2</inf> hydrogenation to methanol and dimethyl ether by Pd-Pd<inf>2</inf>Ga catalysts supported over Ga<inf>2</inf>O<inf>3</inf> polymorphs
2015, Journal of CO2 Utilization
The production of methanol and dimethyl ether (DME) via CO₂ hydrogenation was studied using Pd catalysts supported on α-Ga₂O₃, α-β-Ga₂O₃ and β-Ga₂O₃ polymorphs. The formation of a Pd₂Ga intermetallic compound was observed using XRD and XPS. The catalytic activity improves with an increase in the content of the Pd₂Ga intermetallic compound. The content of Pd₂Ga on Pd/Ga₂O₃ depends on the Ga₂O₃ crystalline phase of the catalyst. A slight catalytic deactivation was observed for all samples studied. The Pd/α-β-Ga₂O₃ catalyst displayed the largest deactivation. The deactivation appears to be caused by a loss of basic sites. The selectivity to dimethyl ether is not dependent on the Pd₂Ga content, but depends on the catalyst acidity. This assertion was tested by adding niobia to the catalysts, thus increasing the DME selectivity from 0 to 53%. The content of Pd₂Ga over Pd/Ga₂O₃ catalysts was identified to be a crucial parameter for CO₂ hydrogenation to methanol.
Hydrogen adsorption on PdGa(100), (111) and (111 ) surfaces: A DFT study
2014, International Journal of Hydrogen Energy
Hydrogen adsorption on PdGa intermetallic compound is analyzed using density functional theory (DFT) calculations. Changes in the electronic structure of PdGa(100), (111) and $(\bar{1} \bar{1} \bar{1})$ surfaces and H bonding after adsorption are addressed. H interacts with Pd atoms with a tilted geometry on (100) and (111) surfaces. On the $(\bar{1} \bar{1} \bar{1})$ surface two possible forms for H adsorption are detected: one is observed atop perpendicular to the surface and the other one is subsuperficial, both with similar adsorption energies. The Ga–H interaction is energetically less stable and is only present on the (100) plane. Pd–Pd bond strength decreases up to 53.8% as the new Pd–H bond is formed. The Pd–H bond length differs less than 1%, compared to the gas phase value for the (100), (111) and atop $(\bar{1} \bar{1} \bar{1})$ . However in the $(\bar{1} \bar{1} \bar{1})$ subsurface-H bond length is about 2.17 Å. The effect of H is limited to its first Pd neighbor. Analysis of orbital interaction reveals that the Pd–H bond mainly involves s–s and s–p orbitals with lower participation of Pd 4d orbitals. The computed H vibration frequencies after adsorption show values of 1786, 1289 and 633.5 cm⁻¹ that correspond to top, bridge and hollow sites respectively.
CO adsorption on PdGa(1 0 0), (1 1 1) and (1¯ 1¯ 1¯) surfaces: A DFT study
2014, Applied Surface Science
Citation Excerpt :
Considering Pd-Ga bond, the s-p contribution is higher than 66% while a p-d contribution is close to 18%. As mentioned before, the PdGa intermetallic compound [22–24] has each Pd atom surrounded by seven Ga atoms. When the planes are generated from the bulk, an isolated Pd atom is exposed.
CO adsorption on (1 0 0), (1 1 1) and $(\bar{1} \bar{1} \bar{1})$ planes is analyzed using density functional theory (DFT) calculations. Changes in the electronic structure of these surfaces and CO bond after adsorption are also addressed here. CO is located on Pd atop geometry with a tilted configuration of 7.8° in the (1 0 0) plane, while in the (1 1 1) and $(\bar{1} \bar{1} \bar{1})$ are perpendicular to the surface. No direct interaction of CO with Ga is detected. The overlap population (OP) of Pd-Pd and Pd-Ga bond decreases as the new Pd-CO bond is formed. In all cases, the C-O bond length changes less than 1% compared to the vacuum but its strength decrease about 50% as determined by the changes in the OP. The effect of CO is limited to its first Pd neighbor. Analysis of orbital interaction reveals that Pd-CO bond mainly involves s-s and s-p orbitals with less participation of Pd 4d orbitals. Computed CO vibration frequencies after adsorption shows a red shift from vacuum towards 1972.9, 1990.4 and 1988.6 cm⁻¹ on (1 0 0), (1 1 1) and $(\bar{1} \bar{1} \bar{1})$ planes respectively, following the same trend that experimental data on the PdGa intermetallic compound.
Methanol steam reforming: CO<inf>2</inf>-selective Pd<inf>2</inf>Ga phases supported on α- And γ-Ga<inf>2</inf>O<inf>3</inf>
2013, Applied Catalysis A: General
A set of different Pd/Ga₂O₃ catalysts has been tested as suitable CO₂-selective catalysts in methanol steam reforming, formaldehyde steam reforming and formic acid decomposition. Special focus was put on two different polymorphic forms of Ga₂O₃, namely α-Ga₂O₃ and γ-Ga₂O₃ and their comparison to the use of the more common β-Ga₂O₃ as oxide support of small Pd particles. The formation of eventually CO₂-selective intermetallic Pd–Ga phases started at around 523 K on both supports. Pd₂Ga at low temperatures (between 523 K and 673 K) and generally PdGa at higher temperatures (at and above 673 K) were the only intermetallic phases observed. Both thermodynamically metastable oxide supports transformed into the stable β-Ga₂O₃ structure at 873 K reduction temperature. In contrast to previous studies, a highly CO₂-selective state in methanol steam reforming (CO₂ selectivity > 70%) could be established on both catalysts after reduction at 673 K (α-Ga₂O₃) and 523 K (γ-Ga₂O₃), where the active state of the catalysts can be characterised as Pd₂Ga/α-Ga₂O₃ and Pd₂Ga/γ-Ga₂O₃, respectively. α-Ga₂O₃ itself is reasonably CO₂-selective in methanol steam reforming (∼80%), although not very active. In contrast, the γ-Ga₂O₃ polymorph is neither CO₂-selective, nor active and resembles the behaviour of β-Ga₂O₃. The high CO₂-selectivity of α-Ga₂O₃ is explained in terms of a higher surface basicity alongside efficient decarboxylation of intermediary formed formic acid. As crucial parameters for the observed CO₂-selectivity in methanol steam reforming, decarboxylation of formic acid and oxidation of formaldehyde proceeding efficiently via a low-temperature reaction channel over either oxide-supported Pd₂Ga intermetallic catalysts were identified.
Ab initio study of CO adsorption on PdGa(1 1 0)
2013, Computational Materials Science
Citation Excerpt :
From the analysis of IR data, Kovnir et al. [9] assigned an on top position for CO on PdGa compound. As mentioned before, the PdGa intermetallic compound [16–18] has each Pd surrounded by seven Ga atoms. When the (1 1 0) plane is generated from the bulk, an isolated Pd atom is exposed.
CO adsorption is analyzed using Density Functional Theory (DFT) calculations. Changes in the electronic structure of PdGa(1 1 0) surface and CO bond after adsorption are addressed. CO is located only on Pd atop geometry with a tilted configuration (9.13° from the perpendicular to the surface) and no interaction with Ga is detected. The Pd–Pd bond strength decreases 54.2% as the new Pd–CO bond is formed. The C–O bond length change less than 1%, compared to the gas phase value, while its bond overlap population decrease 46.2%. The effect of CO is limited to its first Pd neighbor. Analysis of orbital interaction reveals the Pd–CO bond mainly involves s–s and s–p orbitals with less participation of Pd 4d orbitals. The computed CO vibration frequencies after adsorption shows a red shift from vacuum to ward 2013.85 cm⁻¹, which agrees with previous experimental data on PdGa intermetallic.

View all citing articles on Scopus

^∗: Die Untersuchungen an Ni-Pd-Ga bilden einen Teil einer Dissertation von M.K. Bhargava.

View full text

Koexistente phasen vom FeSi-Typ in den mischungen Ni-Pd-Ga und Ni-Pt-Ga

Zusammenfassung

Abstract

J. Less-Common Met.

Jernkontorets Ann.

Z. Kristallogr. Mineral.

Acta Crystallogr.