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Estudios de RMN MAS en estado sólido de sitios de ácido de Brønsted en zeolita H-Mordenita
Hua Huo1, Luming Peng, Zhehong Gan
1Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, USA.
Journal of the American Chemical Society
|May 5, 2012
Resumen
Los investigadores utilizaron técnicas avanzadas de RMN para mapear los sitios de ácido de Brønsted dentro de la zeolita H-Mordenita. Este estudio revela distintas ubicaciones y accesibilidad de sitios ácidos, cruciales para la comprensión de la catálisis de la zeolita.
Área de la Ciencia:
- Espectroscopia de RMN en estado sólido Espectroscopia de RMN en estado sólido
- Química de los materiales Química de los materiales
- La catálisis de la catálisis.
Sus antecedentes:
- Las zeolitas, en particular la H-Mordenita (H-MOR), son catalizadores industriales vitales.
- Comprender la ubicación precisa y la naturaleza de los sitios de ácido de Brønsted es clave para optimizar su rendimiento.
- Los métodos anteriores carecían de la resolución para caracterizar completamente diversos sitios ácidos dentro de H-MOR.
Objetivo del estudio:
- Para aclarar la estructura local y la distribución de los sitios de ácido de Brønsted en H-Mordenite.
- Para diferenciar entre los sitios de ácido de Brønsted en función de sus distancias O-H.
- Para cuantificar la accesibilidad de estos sitios ácidos a las moléculas de sonda.
Principales métodos:
- Se utilizó la espectroscopia de RMN de doble resonancia (17) O-(1) H.
- Se emplean la RMN de giro de ángulo mágico de polarización cruzada (CPMAS), la RMN de doble resonancia de eco y rotación CP (CP-REDOR) y la RMN de correlación heteronuclear (HETCOR).
- Accesibilidad cuantificada del sitio mediante adsorción de trimetilfosfina.
Principales resultados:
- Distintos sitios de ácido de Brønsted con diferentes distancias O-H utilizando diferentes técnicas de RMN y tiempos de contacto.
- Se proponen ubicaciones específicas para diferentes tipos de sitios de ácido de Brønsted dentro del marco H-Mordenite.
- Determinó la accesibilidad de varios sitios de ácido de Brønsted.
Conclusiones:
- El estudio mapeó con éxito diversos sitios de ácido de Brønsted en H-Mordenite.
- La espectroscopia de RMN, en particular la doble resonancia (17) O- ((1) H, es efectiva para la caracterización del sitio.
- (17) Las correlaciones de desplazamiento químico ayudan en la asignación del sitio para la investigación de la zeolita.
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