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Oxidación del metanol a formaldehído en catalizadores de óxido de vanadio apoyados en comparación con las moléculas
Jens Döbler1, Marc Pritzsche, Joachim Sauer
1Institut für Chemie der Humboldt Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany.
Journal of the American Chemical Society
|August 4, 2005
Resumen
La teoría funcional de la densidad investigó la oxidación del metanol a formaldehído en el óxido de vanadio soportado por sílice. El paso de limitación de velocidad implica la transferencia de hidrógeno, con una energía de activación significativamente menor para las especies cargadas.
Área de la Ciencia:
- La catálisis es la catálisis.
- Ciencias de la superficie Ciencias de la superficie.
- Química computacional es la química computacional.
Sus antecedentes:
- La oxidación del metanol a formaldehído es un proceso industrial clave.
- Los catalizadores de óxido de vanadio apoyados en sílice son ampliamente utilizados para esta reacción.
- Comprender el mecanismo de reacción a nivel molecular es crucial para el diseño de catalizadores.
Objetivo del estudio:
- Para dilucidar el mecanismo de la oxidación del metanol al formaldehído en el óxido de vanadio soportado de sílice utilizando métodos computacionales.
- Para identificar el paso que limita la velocidad y el estado de transición.
- Para evaluar la influencia de los sistemas de modelos de catalizadores y la carga en la vía de reacción.
Principales métodos:
- Se emplearon cálculos de la teoría funcional de la densidad (DFT).
- Se utilizaron modelos tipo silsesquioxano para especies aisladas de óxido de vanadio.
- El enfoque de simetría rota se utilizó para tratar los estados de transición biradicaloide.
- Se calcularon las energías de activación para diferentes sistemas modelo.
Principales resultados:
- La adsorción disociativa del metanol forma complejos superficiales CH3O(O=) V(O-) 2.
- El paso que limita la velocidad es la transferencia de hidrógeno del grupo methoxy al oxígeno vanadyl.
- Las energías de activación se calcularon para O=V(OCH3)3 (147 kJ/mol) y el modelo de silsesquioxano (154 kJ/mol).
- Se encontró una barrera de activación significativamente más baja (80 kJ/mol) para el catión radical O=V(OCH3)3(*+).
Conclusiones:
- El estudio proporciona información detallada sobre el mecanismo de oxidación del metanol en el óxido de vanadio soportado.
- El estado de carga de las especies de óxido de vanadio influye fuertemente en la energía de activación de la reacción.
- Los estudios de clúster de fase gaseosa pueden no representar completamente el comportamiento de los catalizadores soportados debido a los efectos de carga.
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