Nanostructured molybdenum chalcogenides: synthesis, structure and catalytic properties
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The catalytic properties of nanostructured molybdenum oxides and sulfides were investigated. Several synthesis methods were tested in order to determine a reliable and reproducible way to produce structurally and chemically homogeneous products. The structure of synthesized molybdenum oxides and sulfides was thoroughly studied by electron microscopy techniques, X-ray diffraction and X-ray photoelectron spectroscopy among others. It was found that the synthesis method of choice produced high yield, single phase, single crystalline molybdenum oxide nanoparticles. These oxide crystals are susceptible to reduction and sulfidation, which enable their use as precursor in the synthesis of molybdenum sulfides. The sulfidation of molybdenum oxide nanocrystals produced highly textured molybdenum sulfide nanostructures. Pseudo one-dimensional structures were identified in these samples. The structural model proposed for such structures implies the presence of sulfur atoms decorating the edges. This is particularly important since these extra-sulfur atoms may lead to an electronic structure different from the bulk molybdenum sulfide. The catalytic properties of these compounds were studied with the model reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT). DBT is considered an appropriate compound for the investigation of the activity and reaction mechanisms of HDS catalysts, and it is widely used in the literature, which facilitates the comparison with reported data. The nanostructured molybdenum compounds showed typical to high activity values, however they presented enhanced selectivity. The oxides were more efficient in the desulfurization of DBT, while the sulfides for hydrogenation.