MAGNETIC METAL NANOPARTICLES AS CATALYST SUPPORTS

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Nanopartículas metálicas magnéticas como suporte de catalisadores

Publication . Fernandes, Cristina Isabel Silva; Nunes, Carla Maria Duarte; Vaz, Pedro Miguel Duarte

In the last few years, nanoscience and nanotechnology have brought a revolution in several areas such as medicine, health, biology, catalysis, communication, environmental protection, and many others. Among these areas, harnessing catalytic processes by using nanoscience remains one of the key areas of research because of its direct implications on human society. Some of the mentioned catalytic processes involve the use of supermagnetic nanoparticles whose interest has increased due to its unique physico-chemical properties, potential aplications across areas, such as, pharmaceutical chemistry, biomedicine/biotechnology or magnetic sensors. In this thesis systems based on metallic magnetic nanoparticles as catalysts support to be applied in olefin epoxidation catalytic reactions have been developed in order to take advantage of the nanoparticles magnetism, for providing easy separation of the catalyst from the reaction slurry. For such, magnetite magnetic nanoparticles (Fe3O4) with different sizes, namely, 11 nm and 30 nm, were sintesized and funcionalized with different organic ligands, namely, a ligand derived from nicotinic acid and another ligand derived from a phosphine. After the functionalization of the magnetic nanoparticles surface with an organic ligand, the metallic fragment [MoI2(CO)3(CH3CN)2] was coordinated to the ligand. The functionalization of the magnetic nanoparticles surface and the coordination of molybdenum metallic fragment was confirmed using suitable characterization techniques, namely, transmission (TEM) and scanning (SEM) electron microscopies, powder X-ray diffraction (DRX), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and Mössbauer spectroscopy. The magnetite magnetic nanoparticles were applied as molybdenum catalysts support in the catalytic epoxidation reaction of a group of olefins and the results were very satisfied regarding to nanoparticles catalytic activity and selectivity. Due to nanoparticles magnetic properties it was possible to remove them from the reaction medium by using an external magnet and reuse them along several catalytic cycles. Keeping in mind the advantages of applying metallic magnetic nanoparticles as catalyst supports, the chemical properties of mesoporous materials with high surface area, such as MCM-41, as nanoparticles support have been explored as well. For such, a mesoporous magnetic nanocomposite was synthesized by impregnation of magnetite magnetic nanoparticles (Fe3O4) in a mesoporous silica matrix. The synthesis of the magnetic nanocomposite was confirmed using suitable microscopic techniques, namely, transmission (TEM) and scanning (SEM) electron microscopies, being possible to verify that this type of materials combined the magnetic properties of the nanoparticles core with the possibility of posterior functionalization characteristic of porous materials, as well as easy recovery and reuse of the catalyst characteristic of magnetic nanoparticles. The activity of the mesoporous magnetic nanocomposite as catalyst support in olefin epoxidation catalytic reactions was studied and it was possible to verify that the nanocomposite is an effective support material. In order to study the influence of the mesoporous material morphology on its catalytic activity, magnetite magnetic nanoparticles were also embedded in the matrix of an helicoidal mesoporous material and, subsequently applied as catalysts support in olefin epoxidation catalytic reactions. In order to study the influence of the metallic center coordinated to the magnetic nanoparticles surface on its catalytic activity, ruthenium was coordinated to nanoparticle´s surface and tested also in olefin epoxidation catalytic reactions. The results presented in this thesis make proof that the iron oxide magnetic nanoparticles exhibit a great potential as catalyst supports in olefin epoxidation catalytic reactions.

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Fundação para a Ciência e a Tecnologia

Número da atribuição

SFRH/BD/81029/2011