Synthesis of TiSBA-15 with low HCl content as catalysts in cyclohexene epoxidation

A series of TiSBA-15 mesoporous materials were synthesised by hydrothermal and wet impregnation method at low HCl content (pH 1.5) (Si/Ti 15 and 30). The calcined samples were characterized by N2 adsorption, FT-IR, DRX, SEM and elementary chemical analysis by atomic absorption. The Ti-containing mesoporous materials showed good textural properties even for load of titanium up to 12% (w/w). FT-IR spectroscopy and elemental analysis provided that it is possible to know the amount of Ti (IV) incorporated into the SBA-15 framework. On our synthesis conditions a limit of 4% (w/w) was found. The catalysts were evaluated in the cyclohexene epoxidation with TBHP (tert-butyl hydroperoxide) as oxidant agent; the selectivity toward cyclohexene epoxide was 100%, and conversion was 50–70% depending on synthesis procedure. It is possible that part of the catalytic response is due to the chemical nature and reactivity of the Ti sources employed. The catalysts obtained by impregnation were more active than that obtained by hydrothermal synthesis for same load of titanium; we cannot discard that non-crystalline TiO2 species co-exist with Ti (IV) isolated and contribute to catalytic activity.

Graphical abstractA series of TiSBA-15 mesoporous materials were synthesised by hydrothermal and wet impregnation procedure at low HCl content (pH 1.5) (Si/Ti 15 and 30). By FT-IR spectroscopy and elemental analysis it is possible to know the level of Ti (IV) incorporation into the framework of SBA-15, on our synthesis conditions a limit at ∼4% (w/w) it was found. The catalysts were evaluated in the cyclohexene epoxidation with TBHP (tert-butyl hydro peroxide); the selectivity toward cyclohexene epoxide was 100%. The catalysts obtained by impregnation (b) were more active than that obtained by hydrothermal synthesis (a) for same load of titanium. TiO2 species co-exist with Ti (IV) isolated and contribute to catalytic activity.Figure optionsDownload full-size imageDownload high-quality image (192 K)Download as PowerPoint slideHighlights► TiSBA-15 mesoporous materials were synthesised at pH 1.5. ► The Ti (IV) incorporation into the framework of SBA-15 has a limit at 4% (w/w). ► All catalysts were selective toward cyclohexene epoxidation. ► Ti/SBA-15 solids (wet impregnation) were more active than Ti-SBA-15 (hydrothermal synthesis). ► TiO2 species co-exist with Ti (IV) isolated and contribute to catalytic activity.