Synthesis of TS-1 from supported embryonic to nano-/micro-metersized crystalline particles: The impact of accessibility of Ti species on the catalytic performance

Abstract

This study reports a seeding-polymer-assisted method using inexpensive tetrapropylammonium bromide (TPABr) to synthesize titanium silicalite-1 (TS-1) ranging from supported embryonic (<8 nm) to crystalline nano-/micrometersized (≈0.1–1.0 μm) particles by kinetic regulation. The in situ grown embryonic TS-1 on the amorphous silica presents defective Ti(OH)(OSi)3, tetrahedral framework Ti (“TiO4”), and extraframework Ti (“TiO6”) species, while crystalline nano-/micro-metersized TS-1 particles exhibit either “TiO4” or both “TiO4” and “TiO6” species and a smaller external surface area, Sext. Turnover frequency (TOF) of TS-1 catalysts in the oxidation of dibenzothiophene (DBT) changes by an order of magnitude with the alteration of active Ti species. For instance, the TOF of supported embryonic TS-1 is 224.3 h−1 while it is 32.6 h−1 for the micro-metersized particles due to differences in the active Ti species. However, the TOF of the different TS-1 samples with similar Ti active sites scales only in proportion to Sext. The supported embryonic TS-1 on amorphous silica presents similar structural and chemical stability in comparison with crystalline nano-/micro-metersized TS-1 catalysts under water-free reaction conditions. Consequently, in situ prepared supported embryonic TS-1 combining improved accessibility (via increased external surface area) of different types of Ti species is a promising alternative for the conversion of bulky substrates.