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Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
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Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
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Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...
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Efectos de apoyo del catalizador sobre el derrame de hidrógeno

Waiz Karim1,2,3, Clelia Spreafico4, Armin Kleibert5

  • 1Institute for Chemical and Bioengineering, ETH Zurich, 8093 Zurich, Switzerland.

Nature
|January 6, 2017
PubMed
Resumen
Este resumen es generado por máquina.

El derrame de hidrógeno, el movimiento de los átomos de hidrógeno activados, se produce rápidamente en soportes de óxido de titanio reducibles, pero es significativamente más lento y limitado en soportes de óxido de aluminio no reducibles. Este estudio cuantifica la eficiencia de derrame en diferentes soportes de catalizadores.

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Área de la Ciencia:

  • Ciencias de los materiales
  • Química de las superficies
  • Catálisis

Sus antecedentes:

  • El derrame de hidrógeno es la migración de hidrógeno activado de los catalizadores metálicos a los soportes.
  • Su aparición en soportes reducibles como el óxido de titanio es conocida, pero su comportamiento en soportes no reducibles como el óxido de aluminio sigue sin estar claro.

Objetivo del estudio:

  • Cuantificar la eficiencia y la extensión espacial del derrame de hidrógeno tanto en soportes reducibles (óxido de titanio) como no reducibles (óxido de aluminio).
  • Investigar los mecanismos de derrame de hidrógeno en diferentes soportes de catalizadores utilizando sistemas de modelos diseñados con precisión.

Principales métodos:

  • Fabricación de sistemas de catalizadores modelo con espaciado de nanopartículas controlado (0-45 nm) utilizando nanofabricación de arriba hacia abajo.
  • Espectromicroscopia de absorción de rayos X in situ para observar la reducción de nanopartículas de óxido de hierro por hidrógeno generado en nanopartículas de platino.
  • Cálculos de la teoría funcional de la densidad para aclarar los mecanismos de derrame.

Principales resultados:

  • Se observó un derrame rápido de hidrógeno en el óxido de titanio, reduciendo las nanopartículas remotas de óxido de hierro a través de la transferencia de protones-electrones.
  • El derrame en el óxido de aluminio es diez órdenes de magnitud más lento y espacialmente restringido, mediado por interacciones con tres centros de aluminio coordinados y agua.
  • La desorción compite con la movilidad del hidrógeno en el óxido de aluminio.

Conclusiones:

  • El estudio aclara los diferentes mecanismos y eficiencias del derrame de hidrógeno en soportes de óxido reducibles versus no reducibles.
  • Los hallazgos mejoran la comprensión del almacenamiento de hidrógeno y las reacciones catalíticas, proporcionando información sobre los efectos sinérgicos en los catalizadores multifuncionales.
  • El enfoque del sistema modelo desarrollado ofrece una plataforma para estudiar las funcionalidades del catalizador admitidas.