Synthesis of Nb-containing mesoporous silica molecular sieves: Analysis of its potential use in HDS catalysts Original Research Article

In the preparation of mesoporous materials of the MCM-41 type, the synthesis aging time is an important parameter that can alter the structural and chemical properties of the final product. This work analyzes the effect of synthesis aging time on the structural and chemical properties of niobium-containing mesoporous silica with two different Si/Nb atomic ratios, 52 and 31. Samples of Nb-modified mesoporous silica were prepared at aging times of 2, 3, 4 and 8 days. The samples were characterized by N2 adsorption measurements, XRD, differential thermogravimetric analysis, FT-IR, pyridine adsorption analyzed by FT-IR, HREM, SEM, DRS and Raman spectroscopy. The results show that synthesis aging time has a definitive influence in the textural, structural and chemical properties of niobium-modified mesoporous silica. Short synthesis aging times (2 days) do not allow the proper incorporation of niobium to the silica framework. With synthesis aging times of 3 and 4 days the niobium is well incorporated to the silica framework. Synthesis aging times up to 4 days promotes the formation of hexagonal structures while aging during 8 days induces the formation of cubic structures. Niobium sulfide has been reported to have good hydrodesulfurization (HDS) and hydrogenation (HYD) activities. The results show that niobium incorporated to the framework of Si-MCM-type materials undergoes partial sulfidation, as attested by the TPS experiments and its small catalytic activity in the thiophene hydrodesulfurization reaction. The solids studied here present therefore an interesting potential application as supports for HDS catalysts.