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Catalizadores de iridio molecular soportados: efectos de resolución de la nuclealidad metálica y soportes como
Jing Lu1, Pedro Serna, Ceren Aydin
1Department of Chemical Engineering and Materials Science, University of California-Davis, One Shields Avenue, Davis, California 95616, United States.
Journal of the American Chemical Society
|August 27, 2011
Resumen
Este estudio revela cómo el rendimiento del catalizador de iridio en la hidrogenación de eteno depende de las propiedades de soporte. Los soportes de MgO donantes de electrones requieren racimos de iridio para la activación de H2, a diferencia de la zeolita HY que retira electrones.
Área de la Ciencia:
- La catálisis heterogénea.
- Ciencias de la superficie Ciencias de la superficie.
- Química de los materiales química de los materiales.
Sus antecedentes:
- El rendimiento del catalizador está dictado por el tamaño del metal, la estructura, los ligandos y el soporte.
- Comprender estos factores es un desafío debido a la falta de sitios catalíticos sistemáticamente variados.
- Las especies de iridio isostruturales ofrecen un modelo para diseccionar estos efectos.
Objetivo del estudio:
- Para dilucidar la influencia de las propiedades de soporte en la hidrogenación de eteno catalizado por iridio.
- Para diferenciar las funciones de los soportes de donación de electrones (MgO) y de retirada de electrones (zeolita HY).
- Para correlacionar la actividad catalítica con el comportamiento del catalizador a nivel molecular.
Principales métodos:
- Síntesis de especies isostruturales de iridio en soportes de MgO y HY de zeolita.
- Análisis espectroscópico in situ de catalizadores de trabajo.
- Estudios cinéticos de la hidrogenación del eteno.
Principales resultados:
- Las velocidades catalíticas en MgO dependen de la disociación de H2, influenciada por la nuclealidad del iridio (mono- vs tetra-nuclear).
- En la zeolita HY, la disociación H2 no limita la velocidad, incluso para átomos de iridio individuales.
- Los sitios de iridio vecinos son cruciales en MgO pero no en HY zeolita para la activación de H2 y eteno.
Conclusiones:
- Las propiedades de soporte alteran significativamente el mecanismo de reacción para la hidrogenación de eteno catalizado por iridio.
- Los soportes de zeolita que retiran electrones facilitan la catálisis incluso a nivel de un solo átomo.
- Los soportes de MgO donantes de electrones requieren sitios de iridio multi-nucleares para una catálisis eficiente.
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