Synthesis of titanosilicate TS-1 crystals via mechanochemical route using low cost materials

Abstract

This paper presents a method for alkoxide-free synthesis of titanium silicalite-1 (TS-1) powder with high catalytic activity using inexpensive materials. A low-grade amorphous silica fume and crystalline anatase-type titania nanoparticles were used as the silicon and titanium sources, respectively. The silica and titania powders were subjected to a mechanochemical treatment under dry conditions using a tumbling ball mill, resulting in the formation of silica–titania nanocomposites as a TS-1 precursor. In order to promote the incorporation of titanium species into the silica matrix in the mechanochemical treatment and to facilitate crystallization in the hydrothermal treatment, the adhesion of the titania nanoparticles was reduced, and aggregates of silica–titania nanocomposites were disintegrated, which were carried out before and after the mechanochemical treatment, respectively. In the hydrothermal treatment, tetrapropylammonium bromide (TPABr) and n-butylamine (NBA) were used as the structure-directing agent (template) for the MFI structure and the weak base, respectively, both of which are relatively inexpensive reagents. Under optimized operating conditions for precursor preparation, large amounts of titanium incorporated into the TS-1 framework were achieved, and the obtained TS-1 powders showed high catalytic activity. For example, the conversion of 1-hexene in the oxidation, using hydrogen peroxide as an oxidant in an acetonitrile solvent, was 12.3%, which is equal to or more than the catalytic activity of TS-1 powders synthesized via conventional sol–gel and mechanochemical methods. The results demonstrate that the modified mechanochemical method is useful and promising for the industrial synthesis of TS-1 powder with high catalytic activity.