Textural and structural properties of niobium-containing micro-, meso- and macroporous molecular sieves

Micro-, meso- and macroporous niobium-containing silicas were synthesized with various silicon and/or niobium sources and/or surfactants. The structure of these materials was characterized by a variety of physico-chemical methods, i.e. nitrogen adsorption, X-ray diffraction, transmission, and scanning electron microscopy. The pore size and surface area of the niobium-containing materials can be systematically varied. The synthesis of the first ordered Nb-silica (NbSM-1, NbSM-2) with ordered mesoporosity by a ligand-assisted vesicle templating strategy was described. These niobium-containing materials have pore sizes in the 50–100 nm range as determined by scanning electron microscopy studies and roughly 5–20 nm mesopores in the same plane as the macropores as determined by transmission electron microscopy and nitrogen adsorption. Niobium-containing SBA-15 mesoporous molecular sieves were synthesized by the hydrolysis of tetraethylorthosilicate in the presence of a niobium source, using a triblock co-polymer as template in acidic medium. The pore size of the NbSBA-15 materials depended strongly on the synthesis conditions as well as the niobium source. All NbSM-X materials appeared to be active as catalysts in oxidation processes.