Phosphate-promoted synthesis of TS-1 thin crystals with Ti(OSi)2(OH)4 species for 1-hexene epoxidation

PO 4 3- assists the one-step synthesis of highly active TS-1 containing Ti-VI species. • PO 4 3- induces plate-like TS-1 morphology and creates hierarchical micropores. • Ti-VI is constructed by Ti-O-PO 4 x- intermediate from bonding of Ti-OH with PO 4 3- . • TS-MAP-0.2 doubles the activity for 1-hexene epoxidation than additive-free TS-1. Titanium silicalite-1 (TS-1) is an efficient and green oxidation catalyst that has been employed in various industrial processes. In our previous work, a highly active TS-1 catalyst bearing Ti(OSi) 2 (OH) 4 (Ti-VI) was successfully prepared via post-treatment with alkaline solutions. Herein, a novel synthesis strategy is developed using monoammonium phosphate (MAP) as a regulator to fabricate thin TS-1 crystals with Ti-VI species, eliminating the complicated post-treatment operations. The study reveals that although the added phosphate anion (PO 4 3- ) is not incorporated into the MFI framework, it significantly affects the crystallization behavior of TS-1 during the synthesis. Essentially, PO 4 3- exerts two functions. First, it regulates the Ti species in the resulting TS-1 by forming Ti-O-PO 4 x - intermediates which not only promotes the formation of Ti-VI but also the construction of large micropores (0.7−0.8 nm) around Ti atoms in TS-1. Furthermore, PO 4 3- induces the formation of plate-like crystal morphology of TS-1. The obtained TS-1 catalyst exhibits remarkably enhanced catalytic performance in 1-hexene epoxidation, which is ascribed to the concurrent o ptimization of its intrinsic catalytic activity and mass transfer diffusion properties. Download: Download high-res image (354KB) Download: Download full-size image