Aerosol Route to TiO ₂ –SiO ₂ Catalysts with Tailored Pore Architecture and High Epoxidation Activity

Abstract

Herein, we present the aerosol-assisted sol–gel preparation of hierarchically porous TiO2–SiO2 catalysts having a spherelike shell morphology and a high Ti dispersion. In order to control the porosity at the micro-, meso-, and macrolevels, we use the evaporation-induced self-assembly (EISA) of a surfactant, possibly combined with polymer beads as hard templates. These catalysts are tested for the epoxidation of cyclohexene with cumene hydroperoxide as the oxidant, and their performance is compared to the reference TS-1 zeolite. The high catalytic performance observed with the catalysts prepared by aerosol stems from their high specific surface area, but also from the short diffusion path length generated by the meso-/macropore architecture which provides entryways for bulky reactants and products. Besides, these materials can incorporate a higher Ti loading than TS-1 zeolite, while ensuring a good control over the Ti speciation. Thus, the unique features of the aerosol process—which is also known to be scalable—allow us to prepare catalytic materials with high epoxidation activity, also for bulky olefins.