CONICET | Buscador de Institutos y Recursos Humanos

Sililacin de un sistema de Fe/MCM-41  Fischer-Tropsch synthesis (FTS) is a process used to produce a broad distribution of clean" hydrocarbons from syngas using principally Fe catalysts. Although it has been used industrially for decades, the main still unresolved problem is to reach a good selectivity toward desirable products. Two main approaches have been applied to this purpose: controlling the operative variables of the process (pressure, contact time, reactor selection or temperature) or modifying the structural properties of the catalysts. The last option is the more promising because the reaction is kinetically controlled. It is generally accepted that FTS is a structure-sensitive reaction. A strategy to increase the selectivity is to obtain a catalyst with a narrow size distribution of active phase crystals which average size is within a determinate range. If a mesoporous solid like MCM-41 ] would be used as iron support and if it would be possible to introduce the iron species mainly inside its channels, the small sizes of the obtained crystals would lead to highly selective catalysts towards the production of light hydrocarbons (HC),since the growth of chain would be limited. Nevertheless, these crystals have an activity smaller than the larger ones . For this reason, the aim of the present work consists in modifying the surface of Fe/MCM-41 catalyst, avoiding the water adsorption, a product of the reaction that leads to active sites poisoning. This surface modification would compensate the activity decrease due to the crystal size. With this purpose a sylilation treatment was carried out to eliminate the supercial hydroxyls, increasing the surface hidrophobicity. Two Fe/MCM-41 systems were obtained with more than 90% of the iron species located inside the support channels, leading to a narrow crystal size distribution, accessible to reactive gases. The samples were characterized by X-ray difraction, atomic absorption spectroscopy, nitrogen adsorption, Mossbauer spectroscopy and Fourier transformer infrared spectroscopy. Moossbauer spectroscopy allowed us to demonstrate that the catalytic active species were the same in both catalysts. The only difference between them was the surface hydrophobicity, that produce a decrease of the \water gas shift reaction in the sylilated catalyst. Besides, this solid is more active for HC production, with a lower methane yield.