Facile synthesis of Ti-TUD-1 for catalytic oxidative desulfurization of model sulfur compounds

Abstract

A facile synthesis route for Ti-TUD-1 at room temperature employing silatrane and titanium glycolate as Si and Ti sources (2–8 mol%), respectively, over a triethanolamine template is proposed. XRD, N2 adsorption–desorption isotherms, and TEM analysis confirmed disordered mesoporous structures with high surface area (715–824 m2/g). According to the UV–visible spectroscopy of the calcined materials, titanium species of ca. 2.7 mol% Ti loading were present mostly in tetrahedral coordination for a sample prepared with 4 mol% Ti in the substrate mixture. Ti-TUD-1 showed catalytic activity in cyclohexene epoxidation, which depended on the amount of tetrahedrally coordinated Ti species. The hydrophilic nature of the surface of Ti-TUD-1 was confirmed by the effect of oxidant such that tert-butyl hydroperoxide (TBHP, 5–6 M in decane) was superior to other oxidants in water (cyclohexene conversion: TBHP in decane 36.5% vs. TBHP in water 30.6%). Ti-TUD-1 was more active in oxidative desulfurization (ODS) reaction than Ti-MCM-41 at the same Ti loading; the former produced 4,6-dimethyldibenzothiophene (4,6-DMDBT) conversion near 100% after reacting for 15 min, whereas Ti-MCM-41 produced final conversion of 4,6-DMDBT of 89% after reacting for 180 min. ODS over Ti-TUD-1 was influenced both by electron density and steric hindrance in model sulfur compounds. Partially polymerized Ti sites seemed to also contribute to the reaction.