Professor, Universidad de Chile; Head, Laboratory of Inorganic Synthesis and Electrochemistry Department of Chemistry, Chile

Speech Title: Synthesis strategies to morphology controlling in rhenium disulfide-carbon composites
Abstract: Rhenium disulfide (ReS2) belongs to a class of layered transition metal dichalcogenides (TMDC) particularly interested as catalysts in hydrodesulfurization (HDS). The incidence of morphology of MoS2-based formulations on their catalytic performance is well known. Attaining reduced lamellae sizes and low stacking degree, favoring reactant access to active sites at sheet edges, is restrained by relatively high van der Waals forces between MoS2 sheets. From this perspective ReS2 appears promising. Its electronic configuration, with one electron more than the MoS2, leads to peculiar intralaminar bonds ―including Re-Re linkages― reducing moreover its tendency to stacking, in an extension that even in bulk it presents a single-layer behavior. In this work we describe the synthesis de ReS2/carbon composites by the hydrothermal reaction (180 °C at auto-generated pressure) of different rhenium salts ―ammonium or alkylammonium and the rhenate(VII) and (IV) complexes― with thiourea. The products, characterized by conventional analytical techniques (e.g. thermal analysis, X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy), in general are amorphous solids with particle size, stacking degree and carbon content which depend on the nature of the rhenium salt used as precursor. The selection of both anion and cation in this salt is important in designing the morphology of resulting composite. The oxidation state of rhenium affects the morphology of the product mainly through the molecular or extended structure of the corresponding oxides, Re2O7 or ReO2, which are the intermediary species in the sulfidation process. Since the alkylammonium cation, concomitantly with the thiourea, is the carbon source for the composite, the carbon content may be easily regulated by adequate selection of the alkylchain length. The volume of the counter ion indeed influences the stacking degree of the rhenium sulfide in the composite. Main results of this work will further discussed by comparing them with the solvent effects in the obtaining of Re2S/C microspheres from the solvothermal reaction of carbonylrhenium (0) with sulfur and its use as catalyst in the HDS reaction [2].
Keywords: Rhenium disulfide; ReS2/C composites; Amorphous materials; Hydrothermal synthesis