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Papel dominante de la entropía en la estabilización de los estados de transición de isomerización del azúcar dentro
Michael J Cordon1, James W Harris1, Juan Carlos Vega-Vila1
1Charles D. Davidson School of Chemical Engineering , Purdue University , 480 Stadium Mall Drive , West Lafayette , Indiana 47907 , United States.
Journal of the American Chemical Society
|September 29, 2018
Resumen
Los microporos de zeolita hidrofóbicos mejoran la catálisis de isomerización del azúcar al reducir la interferencia del agua y estabilizar los estados de transición, lo que lleva a tasas de rotación significativamente más altas en comparación con los poros hidrofílicos. Esto mejora la eficiencia catalítica en soluciones acuosas.
Área de la Ciencia:
- Catálisis
- Ciencias de los materiales
- Química Física
Sus antecedentes:
- Los sitios de ácido de Lewis en las zeolitas son cruciales para la isomerización del azúcar en fase acuosa.
- La influencia de la polaridad de microporos en la actividad catalítica y los mecanismos de reacción sigue siendo incompletamente entendida.
Objetivo del estudio:
- Para dilucidar los efectos del agua coadsorbida en la reacción de isomerización de la glucosa, coordinar paisajes de energía libre dentro de las zeolitas.
- Aclarar las funciones de la adsorción competitiva del agua y la estabilización del estado de transición en microporos hidrofóbicos frente a los hidrofílicos.
Principales métodos:
- Espectroscopia in situ de reflectancia total atenuada en el infrarrojo (IR) y espectroscopia de excitación por modulación.
- Espectroscopia de transmisión IR y cálculos de la teoría funcional de la densidad (DFT).
- Medidas cinéticas de la isomerización de la glucosa en fase acuosa en las zeolitas Ti-Beta.
Principales resultados:
- Las zeolitas beta hidrofóbicas exhiben tasas de rotación de isomerización de glucosa más altas (3-12x) en comparación con las hidrofílicas.
- El agua forma redes de enlace de hidrógeno en microporos hidrofílicos pero no en los hidrofóbicos.
- El confinamiento hidrofóbico reduce la energía libre de Gibbs de los estados de transición de isomerización y reduce el impacto del agua en los sitios activos.
Conclusiones:
- La polaridad de microporos impacta significativamente la isomerización de azúcar catalizada por zeolita al modular la adsorción de agua y la estabilización del estado de transición.
- El confinamiento hidrofóbico mejora el rendimiento catalítico al minimizar la interferencia del agua y estabilizar los intermediarios clave de la reacción.
- La adaptación de la polaridad del microporo de la zeolita ofrece una estrategia prometedora para optimizar los procesos catalíticos en fase líquida.
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