Catalisadores de Pd metálico modificados por líquidos iônicos para a hidrogenação seletiva de compostos poli-insaturados

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

06/08/2012

RESUMO

In this work, heterogeneous catalysts immobilized on supported ionic liquid (IL) were prepared, characterized and investigated in hydrogenation reactions of the substrates 1,5-cyclooctadiene (1,5-COD), trans-cinnamaldehyde (CALD) and nitrobenzene (NB). Two methods were used to prepare the catalysts. In the first, commercial Pd/C catalyst was coated with different amounts of ionic liquids. This method is known as SCILL and consists of a solid catalyst (heterogeneous) covered with IL layers. In the second, Pd nanoparticles were dispersed in IL and supported on the surface of magnetic materials, i) magnetic particles of iron core coated with carbon ([email protected]) and ii) magnetic particles of nickel/molybdenium coated with carbon ([email protected]). This method is known as SILP, and it is related to catalysts immobilized on supported ionic liquid phases. Chapter 1 presents a general introduction about ionic liquids, their properties and applications in catalysis. The types of support used for the catalysts immobilization and hydrogenation reactions are also introduced. Chapter 2 presents the objectives and Chapter 3 describes the experimental work. Chapter 4 shows the preparation and characterization of the Pd/C catalyst coated with different amounts of the ILs 1-hexyl-3-methylimidazolium bromide (HMIm.Br) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm.BF4), prepared by the SCILL method. The amounts of ionic liquid used were 0,5; 1; 2,5; 5 and 10 wt% for HMIm.Br and 1 and 5 wt% for BMIm.BF4. These materials were characterized by X-ray diffraction, thermal analysis and scanning electron microscopy and it was possible to identify the phases of Pd and amorphous carbon, and the presence of IL. The prepared materials were investigated in the hydrogenation reactions of CALD and 1,5-COD. For CALD, the hydrogenation was dependent on the temperature and the amount of IL on the catalyst surface. The increase in the IL layer favored the total hydrogenation. As for 1,5-COD, it was observed an improvement in selectivity for the intermediate cyclooctene (COE). This study showed how the IL can influence the reactions selectivity, both the dissolution of the substrate and products and the interactions IL-substrate can be changed depending on the employee IL. Chapter 5 shows the preparation and characterization of iron magnetic particles coated with carbon [email protected] and the Pd catalyst dispersed in IL supported on [email protected] The support [email protected] was prepared by the CVD method (Chemical Vapor Deposition) at 800°C. The ionic liquid HMIm.Br (1 and 22 wt%) containing dispersed Pd was immobilized on [email protected] to obtain Pd-LI/[email protected] by the impregnation method. Through thermal analysis, infrared spectroscopy and scanning electron microscopy was possible to identify the ionic liquid in the materials. Crystallite average size measurements by X-ray diffraction suggested the Pd crystallites dimensions of approximately 5 nm. The catalysts were used in hydrogenation reactions of 1,5-COD and CALD. For 1,5-COD and CALD with the catalyst Pd-LI/[email protected] prepared with 22 wt% of HMIm.Br, it was observed a low catalyst activity, which was attributed to the relatively high amount of IL immobilized. For the catalyst Pd-LI/[email protected] prepared with 1 wt% of IL, it was observed a different behavior, the activity and selectivity improvement for the hydrogenation of 1,5-COD. As for CALD this same catalyst showed a low activity and selectivity. These results were very interesting with respect to the IL influence in the activity and selectivity of catalysts. Chapter 6 shows the preparation and characterization of the support [email protected] and the Pd catalyst dispersed in the ionic liquid supported on [email protected] (SILP method). The magnetic support [email protected] was prepared by the CVD method at 800°C. The catalysts were dispersed in the IL BMIm.BF4 (1and 2,5 wt%) and immobilized on the magnetic support surface by the impregnation method. Phases of metallic Ni, molybdenum carbide and graphitic carbon were identified through X-ray diffraction analysis. The presence of carbon in the material was also confirmed by TG/DTA. The prepared materials were investigated in hydrogenation reactions of 1,5-COD and NB, and it was possible to study the influence of IL in the activity and selectivity of these catalysts. For 1,5-COD it was observed the improvement in selectivity for the intermediate product COE. For NB it was observed high selectivities to aniline with all the catalysts, with or without IL, however, it was observed the improvement in catalyst activity with the increase in IL layer. This behavior was attributed to the possible interaction between substrate and IL, which favored the access of substrate to catalyst and consequently improved the activity. The Chapter 7 presents the general conclusions of the work

ASSUNTO(S)

química inorgânica  teses.   hidrogenação  teses.   catalisadores  teses.   paladio  teses.  

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