Facile synthesis of efficient and selective Ti-containing mesoporous silica catalysts for toluene oxidation

We report a novel, facile, physical mixing synthetic method that leads to titanium silicate and copper titanium silicate materials or highly effective solid acid catalysts for toluene oxidation reaction. The synthesis involves simple physical mixing of tetraethyl orthosilicate and various titanium alkoxide (and also copper(II) chloride), and then calcination of the products. The effects of the types of precursors on the catalytic activity of the resulting materials are investigated. Notably, titanium(IV) n-butoxide, whose hydrolysis rate is close to that of tetraethyl orthosilicate, yields a material that exhibits strong acidic properties and excellent catalytic activity for toluene oxidation with hydrogen peroxide (H₂O₂) as oxidant, giving 98% conversion of toluene and ca. 100% selectivity to benzaldehyde product. The work demonstrates not only simplicity in terms of synthesis of the materials but also unprecedented solid-acid catalytic activity for titanium silicate materials, the catalytic properties of which can be easily tailored by varying the types of precursors. It is also noteworthy that the materials give among the best catalytic performance (in terms of both conversion and product selectivity) under mild reaction conditions that has been reported for toluene oxidation with H₂O₂ as oxidant for heterogeneous catalysts.