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Promoción del cesio en la epoxidación del estireno en catalizadores de plata
Ling Zhou1, Craig F Gorin, Robert J Madix
1School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA.
Journal of the American Chemical Society
|December 22, 2009
Resumen
La adición de cesio a los catalizadores de plata redirige la oxidación del estireno al óxido de estireno. El cesio estabiliza los intermediarios clave y altera la estructura de la superficie, mejorando el rendimiento del catalizador para la epoxidación selectiva.
Área de la Ciencia:
- Ciencias de la superficie Ciencias de la superficie.
- Catálisis Heterogénea.
- Química de la oxidación Química de la oxidación
Sus antecedentes:
- La oxidación del estireno es un proceso industrial crucial.
- Los catalizadores de plata se utilizan ampliamente para la epoxidación del estireno.
- El control de la selectividad en las reacciones de oxidación sigue siendo un desafío.
Objetivo del estudio:
- Para investigar el efecto de la adsorción de cesio en la selectividad de la oxidación del estireno en Ag110).
- Para aclarar el papel del cesio en la estabilización de los intermediarios de reacción y la modificación de la estructura de la superficie.
- Para comprender los orígenes microscópicos de la influencia del cesio en el rendimiento del catalizador de plata.
Principales métodos:
- Difracción de electrones de baja energía (LEED) para el análisis de la estructura de la superficie.
- Desorción programada por temperatura (TPD) para estudiar las vías de adsorción y reacción.
- Espectroscopia de fotoelectrones de rayos X (XPS) para la determinación de la estructura electrónica (implicado).
Principales resultados:
- La adición de cesio redirige la oxidación del estireno desde el fenilacetaldehído/fenilaceteno al óxido de estireno.
- El cesio estabiliza el intermediario del oxametallaciclo, impidiendo su conversión en productos no deseados.
- Las bajas coberturas de cesio inducen una reconstrucción de la fila faltante (1 x 2) de Ag{110) y un óxido de superficie (3 x 5).
- La estructura de óxido de superficie observada en las microfacetas de Ag111 imita la reactividad de las superficies de Ag111 extendidas.
Conclusiones:
- El cesio actúa como un agente de dirección de la estructura, no un promotor electrónico, en la epoxidación del estireno en Ag{110}.
- La reconstrucción de la superficie y la formación de una fase de óxido de superficie específica son clave para la influencia del cesio en la selectividad.
- Estos hallazgos ofrecen información sobre el diseño de catalizadores selectivos de plata para reacciones de oxidación.
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