Influence of M2+ ions substitution on the structure of lanthanum hexaaluminates with magnetoplumbite structure

Gasperin, M.; Saine, M.C.; Kahn, A.; Laville, F.; Lejus, A.M.

doi:10.1016/0022-4596(84)90131-2

Cited by 105 publications

(40 citation statements)

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“…It is clearly revealed that the Mg ions prefer to occupy the tetrahedral (Al(3)) sites in MP structure as they do in the spinel structure. This result is in good agreement with the X-ray experimental results (9,11), as well as that of our earlier simulation study (20), where the site preference of Mg in the MP structure was determined from the substitution energy in SrAl O . Morgan and Miles (32) suggested that the normal site preferences of cations for tetrahedral or octahedral sites in spinels (33) are presumably paralleled in magnetoplumbite structure also, with the added complexity of competition for, or avoidance of, the nearly trigonal bipyramidal mirror plane sites.…”

Section: Defect Energy Calculationsupporting

confidence: 90%

“…It has been reported that LMA type compounds suffered a loss of divalent cations during crystal growth, leading to a significant departure from their starting compositions (2,11,37,41,42). It was also found that the smaller the content of M>, the higher the disorder in the crystal lattice, the worse the crystal growth, and the more intense the diffuse scattering in (001) planes (11).…”

Section: Defect Complexes Involving »mentioning

confidence: 97%

“…The nonstoichiometric formula LaMg \V Al O \V involved in the A3 process can be expressed also as LaMg W Al O >W . This latter formula was used as initial compositions (0(y(1) for a series of lanthanum hexaaluminates containing diverse divalent cations, by Gasperin et al (11), in order to understand the role played by M> ions in the formation of LMA-type structures. Their structural refinement revealed that the stoichiometries of their grown crystals did not follow the nonstoichiometric formula.…”

Section: Probable Defect Processes Involved In Nonstoichiometric Lmamentioning

confidence: 99%

“…Gasperin et al (11) reported that a whole series of single crystals with LaMn V Al O >V (0(x(1) as a starting composition is obtained, and for x&1, the crystal growth becomes much easier and resulting crystals have a good crystallinity. For , based on the results of structural refinement and chemical analysis.…”

Section: Introductionmentioning

confidence: 98%

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Defect Energetics and Nonstoichiometry in Lanthanum Magnesium Hexaaluminate

Park

Cormack

1997

Journal of Solid State Chemistry

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Section: Defect Energy Calculationsupporting

confidence: 90%

Section: Defect Complexes Involving »mentioning

confidence: 97%

Section: Probable Defect Processes Involved In Nonstoichiometric Lmamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Defect Energetics and Nonstoichiometry in Lanthanum Magnesium Hexaaluminate

Park

Cormack

1997

Journal of Solid State Chemistry

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“…Many papers cover the kinds of coupled-ion substitutions that they have observed in their mineral case. Thus we read, 'The theoretical (sic) REE end-member composition is therefore (my italics) REE R2+AlllO19', when, indeed, not only is this a known structure, but LaR2+AIlIO9, where R --Mg, Co, Mn, Cu etc., have actually been refined by Gasperin et al (1984) and site occupancies of the divalent atom were determined. Early work on these compounds was carried out at the Philips Lab.…”

mentioning

confidence: 99%

Comment on 'zoned hibonites from Punalur, South India'

Morgan

1992

Mineral. mag.

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Structure–Activity Relationships of Nickel–Hexaaluminates in Reforming Reactions Part II: Activity and Stability of Nanostructured Nickel–Hexaaluminate‐Based Catalysts in the Dry Reforming of Methane

Roussière

Schulz

Schelkle³

et al. 2014

ChemCatChem

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Ni–hexaaluminates exhibiting a high magnetoplumbite or β“‐alumina phase content (>80 wt %) and high specific surface areas (10–30 m2 g−1) were investigated under dry reforming conditions. Ni content and choice of mirror plane cation are the key factors controlling the structure–property relationship in the dry reforming reaction of CH4. The Ni content is favorably kept below a threshold of y=0.25 in ANiyAl12‐yO19−δ, (A=Ba, La, Sr) to ensure controlled nanoparticle formation and to avoid uncontrolled Ni0 nanoparticle growth apart from the support. Sr,Ni and Ba,Ni–hexaaluminates promote high activity of the catalyst in the dry reforming reaction of CH4, but show fast deactivation if the Ni content is maladjusted in the hexaaluminate framework (y≥0.5). La,Ni–magnetoplumbites display much lower activity accompanied by fast deactivation. The use of very high calcination temperatures (1600 °C) resulting in low specific surface area is detrimental to the activity in the dry reforming of CH4, simultaneously higher hexaaluminate phase content obtained undoes catalytic stability, reasoned by Ni0 nanoparticles produced after reduction cannot be stabilized over surface defects typically found on hexaaluminate platelets calcined at moderated temperatures (<1300 °C). As a result, larger metallic Ni ensembles are built up, selectivity to coke is increased and catalytic stability is compromised.

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Influence of M2+ ions substitution on the structure of lanthanum hexaaluminates with magnetoplumbite structure

Cited by 105 publications

References 10 publications

Defect Energetics and Nonstoichiometry in Lanthanum Magnesium Hexaaluminate

Defect Energetics and Nonstoichiometry in Lanthanum Magnesium Hexaaluminate

Comment on 'zoned hibonites from Punalur, South India'

Structure–Activity Relationships of Nickel–Hexaaluminates in Reforming Reactions Part II: Activity and Stability of Nanostructured Nickel–Hexaaluminate‐Based Catalysts in the Dry Reforming of Methane

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