TY - JOUR
T1 - Effect of AI3+ introduction into hydrothermally prepared ZnFe2O4
AU - Toledo, J. A.
AU - Valenzuela, M. A.
AU - Bosch, P.
AU - Armendáriz, H.
AU - Montoya, A.
AU - Nava, N.
AU - Vázquez, A.
PY - 2000/5/15
Y1 - 2000/5/15
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.
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.
KW - Aluminum zinc ferrite
KW - Ferrites
KW - Hydrothermal method
KW - Mixed oxides
KW - Mössbauer spectra
KW - Oxidative dehydrogenation
KW - Spinel
UR - http://www.scopus.com/inward/record.url?scp=0034658639&partnerID=8YFLogxK
U2 - 10.1016/S0926-860X(99)00514-1
DO - 10.1016/S0926-860X(99)00514-1
M3 - Artículo
SN - 0926-860X
VL - 198
SP - 235
EP - 245
JO - Applied Catalysis A: General
JF - Applied Catalysis A: General
IS - 1-2
ER -