Synthesis of bimodal mesoporous titanosilicate beads and their application as green epoxidation catalyst

• Bimodal mesoporous titanosilicate beads as active catalyst for epoxidations of alkenes with aqueous H2O2.
• Higher turnover frequency (TOF) values and higher yields to the relevant epoxides with the beads compared with Ti-MCM-41.
• More accessible Ti species in the beads via the continuous large mesopore system.
• A stable bead catalyst immune to titanium leaching.

Bimodal mesoporous titanosilicate beads with interconnected three-dimensional pore architecture (BMB-TiSil) were synthesized through a one-pot dual-templating method in the presence of a porous anion-exchange resin. Whereas the framework mesopores centered at 3.5 nm are generated by the templating effect of the surfactant, the continuous large mesopore system originates from removal of the resin body. In the green epoxidations of alkene with aqueous H2O2, BMB-TiSil showed higher turnover frequency (TOF) based on the alkene conversion and higher epoxide yield than Ti-MCM-41, which is mainly ascribed to the continuous large mesopore system favoring the diffusion of the reactants and products to and from the active titanium sites. Importantly, BMB-TiSil is a stable catalyst immune to titanium leaching, and can be reused in three successive catalytic cycles without significant loss of activity due to its continuous large mesopore system and stable Ti-sites.

Titanosilicate beads with bimodal mesoporosity displayed improved catalytic behavior in the epoxidations of cyclohexene and other alkenes bulkier than cyclohexene with aqueous H2O2 compared with Ti-MCM-41. The continuous large mesopore system in the beads favors the diffusion of the reactants to the active titanium sites.Figure optionsDownload high-quality image (185 K)Download as PowerPoint slide