Mesoporous niobium oxyhydroxide catalysts for cyclohexene epoxidation reactions

Abstract

Mesoporous catalysts were synthesized from the precursor NbCl5 and surfactant CTAB (cetyltrimethylammonium bromide), using different synthesis routes of, in order to obtain materials with different properties which are capable of promoting the epoxidation of cyclohexene. The materials were characterized by X ray diffractometry (XRD), thermogravimetry (TG), acidity via pyridine adsorption, Hammet titration and N2 adsorption/desorption. The characterization data indicate that the calcination process of the catalysts was efficient for elimination of the surfactant, but it caused a collapse of the structure, causing a Brunauer Emmett Teller (BET) specific area decrease (ClNbS-600, 44 and ClNbS-AC-600, 64 m2 g-1). The catalysts that have not been calcined showed high BET specific areas (ClNbS 198 and ClNbS-AC 153 m2 g-1). Catalytic studies have shown that mild reaction conditions promote high conversion. The catalysts ClNbS and ClNbS-AC showed high conversions of cyclohexene, 50 and 84%, respectively, while the calcined materials showed low conversion ( < 30%). The epoxide formation was confirmed by nuclear magnetic resonance (NMR).