Diol-Directed Pore Aperture Control in Polymer-Derived Titanium-Silica Oxides Enables Selective Cyclohexene...

Precise control of pore apertures remains a central challenge in the synthesis and application of porous materials. For titanium-silica oxides, this control is especially difficult because titanium alkoxides hydrolyze and condense faster than silicon alkoxides, compromising the homogeneous distribution of Ti species under conventional sol-gel conditions. Here we show that Ti-diol-Si polymers provide a direct route to pore-aperture control in porous titanium-silica oxides, allowing pore structures to be systematically varied from the microporous to mesoporous regime. The polymers were prepared by transesterification of titanium and silicon alkoxides with diols of different sizes and flexibilities, from 1,3-propanediol (PDO) to polyethylene glycol 400 (PEG400). The diol segments act as reactive linkers and removable molecular spacers, translating diol structure into pore architecture after calcination. The resulting oxides retain dispersed Ti─O─Si environments and show surface areas up to 1053 m² g^-1, with systematically varied pore and external surface areas. In cyclohexene epoxidation with tert-butyl hydroperoxide (TBHP) in acetonitrile, the PEG400-derived oxide gives a turnover number of 487.6% and 97.9% selectivity to cyclohexene oxide. This work establishes a diol-polymer route to pore-aperture control in Ti─Si mixed oxides.