Influence of surfactants on the physicochemical properties and catalytic behaviour of Mo-doped carbon xerogels

Abstract

A series of Mo-doped carbon xerogels were obtained by surfactant-assisted sol-gel polymerization of resorcinol-formaldehyde at neutral pH. The morphology, porous texture, acid-base character and metal phase and dispersion, of these novel nanostructured materials were studied by several and complementary techniques, while their catalytic performance was assessed in the isopropanol decomposition and n-hexane aromatization. The formation of different carbon nanostructures (nanospheres or nanofibers) was induced by fitting the surfactant ratios, being always obtained highly dispersed molybdenum nanoparticles on these nanostructures. Nevertheless, the nature of the Mo-phases varied from oxides to carbides depending on surfactant ratios. The incorporation of cationic surfactant molecules to the chemical structure of the gels favours the interaction with anionic precursors, like MoO42−, which avoids sintering and promotes the carbidization of the metallic phase (63% of the total metal loading being achieved) during carbonization. The combination of Mo-phases (oxide and carbide) together the carbon support moderates the catalyst acidity, which induces a high selectivity to benzene (around 75%) in hexane aromatization processes.