Efecto del tratamiento hidrotérmico sobre las propiedades magnéticas de catalizadores del tipo MCM-41 modificados con hierro
Date
2016
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Abstract
Se sintetizaron catalizadores de estructuras altamente ordenadas del tipo MCM-41 modificados con
hierro por un método de síntesis directa. Por medio del análisis de las isotermas de adsorción de N2, los
espectros UV-Vis RD y las medidas de comportamiento magnético de las muestras se estudió el efecto
refinador del tratamiento hidrotérmico y su consecuente influencia sobre propiedades estructurales y
magnéticas. Se identificaron las diferentes especies metálicas (cationes aislados en la red, nanoclusters,
nanopartículas de óxidos de tamaños muy pequeños y nanopartículas de mayor tamaño). Las cuales, según
su cantidad relativa y tamaño dan lugar a las diferencias en el comportamiento magnético de las muestras.
Así, la muestra sin dicho tratamiento presentó un comportamiento magnético resultante de la combinación
de tres contribuciónes: paramagnética, superparamagnética e interacciones ferromagnéticas. En tanto, a
medida que se incrementa el tiempo de síntesis hidrotérmico se refuerza la estabilización del hierro en la
red con una menor segregación de especies de óxido. Esto conduce a un comportamiento
superparamagnético proveniente del menor tamaño de las nanoespecies y paramagnético debido a la
mayor cantidad de cationes de hierro en la red.
Highly ordered structures catalysts of MCM-41 type modified with iron by a direct synthesis method were synthesized. Through analysis of the N2 adsorption isotherms, UV-Vis spectra and measures magnetic behavior of samples, the refiner effect of hydrothermal treatment and its consequent influence on structural and magnetic properties were studied. Different metal species (isolated cations framework, nanoclusters, nanoparticles of oxides of very small sizes and larger nanoparticles) were identified. Which, depending on size and quantity result in differences in the magnetic behavior of the samples. Thus, the sample without such treatment presented a resulting magnetic behavior of the combination of three contributions: paramagnetic, superparamagnetic and ferromagnetic interactions. Meanwhile, time longer synthesis stabilized the iron cations in the framework and reinforced the segregation of smaller oxide species. This leads to a superparamagnetic behavior (from the smaller size nanoespecies) and paramagnetic behavior (due to the greater amount of iron cations in the framework).
Highly ordered structures catalysts of MCM-41 type modified with iron by a direct synthesis method were synthesized. Through analysis of the N2 adsorption isotherms, UV-Vis spectra and measures magnetic behavior of samples, the refiner effect of hydrothermal treatment and its consequent influence on structural and magnetic properties were studied. Different metal species (isolated cations framework, nanoclusters, nanoparticles of oxides of very small sizes and larger nanoparticles) were identified. Which, depending on size and quantity result in differences in the magnetic behavior of the samples. Thus, the sample without such treatment presented a resulting magnetic behavior of the combination of three contributions: paramagnetic, superparamagnetic and ferromagnetic interactions. Meanwhile, time longer synthesis stabilized the iron cations in the framework and reinforced the segregation of smaller oxide species. This leads to a superparamagnetic behavior (from the smaller size nanoespecies) and paramagnetic behavior (due to the greater amount of iron cations in the framework).
Description
Keywords
Mesoporosos, Superparamagnéticos, Tratamiento hidrotérmico
Citation
XXVI Congreso Iberoamericano de Catálisis (2016).
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