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Selectividad del benceno en la hidrogenación competitiva del areno: efectos del catalizador de un solo sitio y la
Weixing Gu1, Madelyn Marie Stalzer1, Christopher P Nicholas2
1†Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Journal of the American Chemical Society
|April 18, 2015
Resumen
Los catalizadores de organozirconio en óxidos ácidos hidrogenan eficientemente el benceno. La actividad y la selectividad del catalizador dependen de la acidez superficial y la masa estérica, lo que ofrece ideas para eliminar el benceno de la gasolina.
Área de la Ciencia:
- La catálisis heterogénea.
- Química organometálica de las sustancias orgánicas.
- Ciencias de la superficie Ciencias de la superficie.
Sus antecedentes:
- La hidrogenación del benceno es crucial para eliminar el benceno cancerígeno de la gasolina.
- Los complejos de organozirconio soportados en óxidos ácidos son prometedores como catalizadores.
- Comprender las relaciones estructura-actividad es clave para optimizar el rendimiento del catalizador.
Objetivo del estudio:
- Investigar la actividad y la selectividad de los catalizadores de organozirconio para la hidrogenación del benceno.
- Explorar la influencia de la acidez del soporte y la masa estérica del catalizador en el rendimiento catalítico.
- Para dilucidar el mecanismo de hidrogenación del benceno utilizando métodos espectroscópicos y computacionales.
Principales métodos:
- Quemisorción de los complejos de organozirconio (Cp*ZrMe3, Cp*ZrBz3, Cp*ZrPh3) en los óxidos ácidos de Brønsted (ZrO2 sulfatado, Al2O3 sulfatado, ZrO2-WO3).
- Reacciones de hidrogenación del benceno en condiciones suaves (25 °C, 1 atm H2) utilizando mezclas de benceno/areno.
- Caracterización utilizando espectroscopia de RMN de estado sólido, espectroscopia de absorción de rayos X (XAS) y cálculos de la teoría funcional de la densidad periódica (DFT).
Principales resultados:
- La actividad del catalizador se correlaciona positivamente con la acidez de Brønsted del soporte (ZrS > AlS ≈ ZrW).
- La selectividad de la hidrogenación del benceno está influenciada por la estructura del catalizador y el obstáculo estérico, con Cp*ZrBz3/ZrS mostrando alta actividad y selectividad moderada.
- Los grupos benzílicos voluminosos en los catalizadores de organozirconio expanden las distancias de soporte de metal, debilitando el emparejamiento iónico y permitiendo la activación de arenas estéricamente gravadas.
Conclusiones:
- La acidez de Brønsted del soporte juega un papel crítico en la mejora de la actividad del catalizador de organozirconio para la hidrogenación del benceno.
- Los factores estéricos, particularmente el tamaño de los grupos de ligandos en el zirconio, afectan significativamente las tasas de hidrogenación y la selectividad.
- Los hallazgos proporcionan información valiosa sobre el diseño de catalizadores eficientes para la eliminación selectiva de benceno de las corrientes de combustible.
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