Effect of AI<sup>3+</sup> introduction into hydrothermally prepared ZnFe<inf>2</inf>O<inf>4</inf>

J. A. Toledo, M. A. Valenzuela, P. Bosch, H. Armendáriz, A. Montoya, N. Nava, A. Vázquez

Research output: Contribution to journalArticle

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Abstract

The effect of aluminum introduction into the zinc ferrite ZnFe2-xAlxO4 spinel structure was studied in the concentration range of 0.0 ≤ x ≤ 1.0. Spinel ferrites were obtained by hydrothermal method at 140°C in the whole range of Al concentration (x). The resulting powders were calcined at 550 and 750°C, and their physicochemical and catalytic properties were compared with those prepared by coprecipitation method [J.A. Toledo, P. Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. 125 (1997) 53]. As in coprecipitated samples, isomorphic substitution of Fe3+ by Al3+ into the octahedral sites was observed. The aluminum introduction gives rise to a lattice distortion caused by the introduction of a metal with smaller atomic radius. This lattice distortion facilitates a charge transfer from Fe3+ to O2-, which increases the basicity of the oxygen atoms in the Fe-O-Al bonds, increasing its proton affinity. Therefore, it favors the acid-base dissociation that takes place in the C-H bond during the abstraction of the hydrogen atom in the oxidative dehydrogenation (OXD) process. After calcination at 550°C, a maximum in the intrinsic activity and butadiene yield was obtained for an Al concentration of 0.2 ≤ x ≤ 0.5, whereas in coprecipitated catalysts, a higher aluminum content was necessary (0.75 ≤ x ≤ 1.0). In the hydrothermally treated samples calcined at 750°C, the promoter effect of aluminum was not evident. Indeed, the pure ZnFe2O4 showed the maximum activity to butadiene. However, the activity of the structural surface sites increased by a factor about 2 as the calcining temperature increased from 550 to 750°C. © 2000 Elsevier Science B.V. All rights reserved.
Original languageAmerican English
Pages (from-to)235-245
Number of pages210
JournalApplied Catalysis A: General
DOIs
StatePublished - 15 May 2000
Externally publishedYes

Fingerprint

Aluminum
ferrite
aluminum
spinel
Butadiene
Atoms
Hydrogen
Ferrites
substitution
Dehydrogenation
Alkalinity
Coprecipitation
zinc
catalyst
hydrogen
Powders
Calcination
Ferrite
Protons
Charge transfer

Cite this

Toledo, J. A. ; Valenzuela, M. A. ; Bosch, P. ; Armendáriz, H. ; Montoya, A. ; Nava, N. ; Vázquez, A. / Effect of AI<sup>3+</sup> introduction into hydrothermally prepared ZnFe<inf>2</inf>O<inf>4</inf>. In: Applied Catalysis A: General. 2000 ; pp. 235-245.
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abstract = "The effect of aluminum introduction into the zinc ferrite ZnFe2-xAlxO4 spinel structure was studied in the concentration range of 0.0 ≤ x ≤ 1.0. Spinel ferrites were obtained by hydrothermal method at 140°C in the whole range of Al concentration (x). The resulting powders were calcined at 550 and 750°C, and their physicochemical and catalytic properties were compared with those prepared by coprecipitation method [J.A. Toledo, P. Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. 125 (1997) 53]. As in coprecipitated samples, isomorphic substitution of Fe3+ by Al3+ into the octahedral sites was observed. The aluminum introduction gives rise to a lattice distortion caused by the introduction of a metal with smaller atomic radius. This lattice distortion facilitates a charge transfer from Fe3+ to O2-, which increases the basicity of the oxygen atoms in the Fe-O-Al bonds, increasing its proton affinity. Therefore, it favors the acid-base dissociation that takes place in the C-H bond during the abstraction of the hydrogen atom in the oxidative dehydrogenation (OXD) process. After calcination at 550°C, a maximum in the intrinsic activity and butadiene yield was obtained for an Al concentration of 0.2 ≤ x ≤ 0.5, whereas in coprecipitated catalysts, a higher aluminum content was necessary (0.75 ≤ x ≤ 1.0). In the hydrothermally treated samples calcined at 750°C, the promoter effect of aluminum was not evident. Indeed, the pure ZnFe2O4 showed the maximum activity to butadiene. However, the activity of the structural surface sites increased by a factor about 2 as the calcining temperature increased from 550 to 750°C. {\circledC} 2000 Elsevier Science B.V. All rights reserved.",
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Effect of AI<sup>3+</sup> introduction into hydrothermally prepared ZnFe<inf>2</inf>O<inf>4</inf> / Toledo, J. A.; Valenzuela, M. A.; Bosch, P.; Armendáriz, H.; Montoya, A.; Nava, N.; Vázquez, A.

In: Applied Catalysis A: General, 15.05.2000, p. 235-245.

Research output: Contribution to journalArticle

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AU - Toledo, J. A.

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N2 - The effect of aluminum introduction into the zinc ferrite ZnFe2-xAlxO4 spinel structure was studied in the concentration range of 0.0 ≤ x ≤ 1.0. Spinel ferrites were obtained by hydrothermal method at 140°C in the whole range of Al concentration (x). The resulting powders were calcined at 550 and 750°C, and their physicochemical and catalytic properties were compared with those prepared by coprecipitation method [J.A. Toledo, P. Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. 125 (1997) 53]. As in coprecipitated samples, isomorphic substitution of Fe3+ by Al3+ into the octahedral sites was observed. The aluminum introduction gives rise to a lattice distortion caused by the introduction of a metal with smaller atomic radius. This lattice distortion facilitates a charge transfer from Fe3+ to O2-, which increases the basicity of the oxygen atoms in the Fe-O-Al bonds, increasing its proton affinity. Therefore, it favors the acid-base dissociation that takes place in the C-H bond during the abstraction of the hydrogen atom in the oxidative dehydrogenation (OXD) process. After calcination at 550°C, a maximum in the intrinsic activity and butadiene yield was obtained for an Al concentration of 0.2 ≤ x ≤ 0.5, whereas in coprecipitated catalysts, a higher aluminum content was necessary (0.75 ≤ x ≤ 1.0). In the hydrothermally treated samples calcined at 750°C, the promoter effect of aluminum was not evident. Indeed, the pure ZnFe2O4 showed the maximum activity to butadiene. However, the activity of the structural surface sites increased by a factor about 2 as the calcining temperature increased from 550 to 750°C. © 2000 Elsevier Science B.V. All rights reserved.

AB - The effect of aluminum introduction into the zinc ferrite ZnFe2-xAlxO4 spinel structure was studied in the concentration range of 0.0 ≤ x ≤ 1.0. Spinel ferrites were obtained by hydrothermal method at 140°C in the whole range of Al concentration (x). The resulting powders were calcined at 550 and 750°C, and their physicochemical and catalytic properties were compared with those prepared by coprecipitation method [J.A. Toledo, P. Bosch, M.A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. 125 (1997) 53]. As in coprecipitated samples, isomorphic substitution of Fe3+ by Al3+ into the octahedral sites was observed. The aluminum introduction gives rise to a lattice distortion caused by the introduction of a metal with smaller atomic radius. This lattice distortion facilitates a charge transfer from Fe3+ to O2-, which increases the basicity of the oxygen atoms in the Fe-O-Al bonds, increasing its proton affinity. Therefore, it favors the acid-base dissociation that takes place in the C-H bond during the abstraction of the hydrogen atom in the oxidative dehydrogenation (OXD) process. After calcination at 550°C, a maximum in the intrinsic activity and butadiene yield was obtained for an Al concentration of 0.2 ≤ x ≤ 0.5, whereas in coprecipitated catalysts, a higher aluminum content was necessary (0.75 ≤ x ≤ 1.0). In the hydrothermally treated samples calcined at 750°C, the promoter effect of aluminum was not evident. Indeed, the pure ZnFe2O4 showed the maximum activity to butadiene. However, the activity of the structural surface sites increased by a factor about 2 as the calcining temperature increased from 550 to 750°C. © 2000 Elsevier Science B.V. All rights reserved.

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