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).
Highlights
The use of molecular sieves has been of great industrial interest, since they direct the reactions due to their defined porous structure, being able to promote a greater selectivity for the product of interest
No significant mass loss events were observed for calcined catalysts (ClNbS-600 and ClNbS-AC-600); which means that the calcination temperature was sufficient to remove all surfactant and hydroxyls, leaving only
The results results presented presented an efficient catalytic process using niobium oxyhydroxide synthesized synthesized from the precursor analysis showed the incorporation of in the structure of the from the precursor NbCl5
Summary
The use of molecular sieves has been of great industrial interest, since they direct the reactions due to their defined porous structure, being able to promote a greater selectivity for the product of interest. Niobium compounds stand out among those of neighboring elements because of their bifunctional properties, since they may have high acidity and ability to form highly oxidizing species in the presence of H2 O2 by the formation of peroxo (Nb-O-OH) surface groups [3]. This allows their oxides to be widely used in heterogeneous catalysis in several types of reactions [4]. Selective oxidation reactions are less thermodynamically favored than those that promote total oxidation, necessitating a suitable catalyst to direct the formation of the product of kinetic interest [7]
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