Farbe und Konstitution bei anorganischen Feststoffen. III Die Lichtabsorption des dreiwertigen Chroms

The effect of alumina structure (γ‐, η‐, χ‐Al2O3) on the long‐term stability of industrial‐like Cr2O3/Al2O3 dehydrogenation catalysts under industrial dehydrogenation conditions is studied. It is shown that the type of alumina support determines physicochemical and catalytic stability of the catalyst: η‐Al2O3 is the most stable against irreversible deactivation, whereas χ‐Al2O3 is the least stable. One of the possible reasons of predominant stability of η‐Al2O3‐based catalyst is its relatively high sintering stability under real plant conditions. High‐temperature (>800 °C) calcination, sometimes used to compare stabilities of chromia/alumina catalysts, appears to be unable to simulate industrial aging because of the inconsistency of the phase composition of industrially and artificially aged catalysts.

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The Effect of Transition Alumina (γ‐, η‐, χ‐Al₂O₃) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions

Назимов

Климов

Шаверина

et al. 2019

Energy Tech

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Structural stability, cation ordering, and local relaxation along the AlNbO4-Al0.5Cr0.5NbO4 join

Ardit

Dondi

Cruciani

2012

American Mineralogist

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(Al1–xCrx)3+Nb5+O4 (with 0 ≤ x ≤ 0.5) compounds have been investigated through the combination of X-ray powder diffraction (XRPD) and electronic absorption spectroscopy (EAS). In spite of the natural occurrence of AlTaO4, the lack of a mineral with composition AlNbO4 contrasts with the strong geochemical affinity between Nb and Ta elements. Rietveld refinements of XRPD data showed that the effective coordination numbers of the two non-equivalent octahedral sites (M1 and M2) in the AlNbO4 structure are much lower than expected, especially the one mainly occupied by Nb. This is in agreement with the very low crystal field strength values (10Dq) found by EAS for Cr3+ replacing Al at site M2. These findings imply that an unfavorable bonding situation occurs for Nb, Al, and Cr ions in the AlNbO4 structure, which can be regarded as substantially strained compared to AlTaO4, thus explaining the lack of a natural AlNbO4 isomorph. The observed long local Cr–O distances (low 10Dq) reveal that the AlNbO4 lattice is not relaxed as a consequence of the Cr–Al substitution (the relaxation coefficient ε is close to zero) and the AlNbO4 structure appears to follow the Vegard’s law. This is due to the fact that the Cr3+ for Al3+ substitution, for the limited range of solid solution (up to 0.2 apfu at site M2), does not induce any additional octahedral strain in a lattice already significantly strained

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Crystal Chemistry and Color of Inorganic Compounds

Ohtsuka¹

1985

J. Jpn. Soc. Colour Mater.

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Farbe und Konstitution bei anorganischen Feststoffen. III Die Lichtabsorption des dreiwertigen Chroms

Cited by 3 publications

References 13 publications

The Effect of Transition Alumina (γ‐, η‐, χ‐Al₂O₃) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions

The Effect of Transition Alumina (γ‐, η‐, χ‐Al₂O₃) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions

Structural stability, cation ordering, and local relaxation along the AlNbO4-Al0.5Cr0.5NbO4 join

Crystal Chemistry and Color of Inorganic Compounds

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Farbe und Konstitution bei anorganischen Feststoffen. III Die Lichtabsorption des dreiwertigen Chroms

Cited by 3 publications

References 13 publications

The Effect of Transition Alumina (γ‐, η‐, χ‐Al2O3) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions

The Effect of Transition Alumina (γ‐, η‐, χ‐Al2O3) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions

Structural stability, cation ordering, and local relaxation along the AlNbO4-Al0.5Cr0.5NbO4 join

Crystal Chemistry and Color of Inorganic Compounds

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Product

Resources

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The Effect of Transition Alumina (γ‐, η‐, χ‐Al₂O₃) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions

The Effect of Transition Alumina (γ‐, η‐, χ‐Al₂O₃) on the Activity and Stability of Chromia/Alumina Catalysts. Part II: Industrial‐Like Catalysts and Real Plant Aging Conditions