Catalizadores de Au-Ir soportados en óxidos reducibles para hidrogenación de aldehídos α, β-insaturados
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En la presente memoria de tesis se describe el uso de catalizadores de Au, Ir e Au-Ir soportados en óxidos reducibles para la hidrogenación selectiva de aldehídos α, β-insaturados. Se estudió, el efecto del contenido de metal, temperaturas de reducción y método de preparación del sistema Au-Ir. A bajas relaciones atómicas de Au/Ir se evidencia la formación de sitios Irδ+ independiente de la temperatura de reducción empleada, fenómeno que no es observado cuando la proporción de oro incrementa. Sitios activos de distinta naturaleza para la adsorción de citral y adsorción disociativa de hidrógeno parecen ser los responsables por la actividad catalítica observada. Es necesario la formación de sitios activos hidrogenantes y selectivos, como fue comprobado por un nuevo método de deposición de coloides metálicos. Una combinación de pequeñas partículas y la presencia de sitios de oro cargados negativamente parecen ser necesarios para incrementar la selectividad a la hidrogenación del grupo C=O. Se aportó al conocimiento de sistemas bimetálicos y a la explicación de su comportamiento catalítico.
Abstract. In this thesis, Au, Ir and Au-Ir catalysts for the hydrogenation of α, β-unsaturated aldehydes were evaluated. The influence of the metal content, reduction temperature and preparation method was studied. The formation of Irδ+ sites independent of the reduction temperature at low ratios was evidenced. This phenomenon is not observed when the gold proportion increases; in these activesites with different nature seems be responsibles of the catalytic activity observed. It is necessary to increase the extent of Irδ+ sites for a better catalytic behavior, as was checked by colloids deposition. A combination of small particles and the presence of gold sites negatively charged seem to be necessary to enhance the selectivity to hydrogenation of the C=O bond. This thesis it is a contributed to knowledge of bimetallic systems and the explanation of its catalytic behavior.
Abstract. In this thesis, Au, Ir and Au-Ir catalysts for the hydrogenation of α, β-unsaturated aldehydes were evaluated. The influence of the metal content, reduction temperature and preparation method was studied. The formation of Irδ+ sites independent of the reduction temperature at low ratios was evidenced. This phenomenon is not observed when the gold proportion increases; in these activesites with different nature seems be responsibles of the catalytic activity observed. It is necessary to increase the extent of Irδ+ sites for a better catalytic behavior, as was checked by colloids deposition. A combination of small particles and the presence of gold sites negatively charged seem to be necessary to enhance the selectivity to hydrogenation of the C=O bond. This thesis it is a contributed to knowledge of bimetallic systems and the explanation of its catalytic behavior.