Synthesis of Plate-Like TS-1 Zeolites with a Controllable <i>b</i>-Axis Thickness and Ti Coordination States

Developing an approach for the efficient synthesis of TS-1 zeolites with desirable morphologies and tunable coordination environments for Ti active sites is a pivotal challenge in the design of high-performance catalysts and zeolite crystal engineering. Herein, we report a cost-effective and efficient additive, guanidinoacetic acid (GAA), and conduct a systematic study on the synthesis of plate-like TS-1 zeolites using GAA as an additive. Introducing GAA during hydrothermal synthesis not only modulates the morphology of TS-1 crystals but also permits GAA to adequately chemically interact with titanium precursors to form hexa-coordinated Ti species. TS-1 zeolites with a controllable b-axis thickness in the range of 80–110 nm, and abundant framework Ti and hexa-coordinated Ti species are successfully achieved by optimizing the synthetic parameters. Through SEM, FT-IR, XPS, TEM, and XRD analysis, the mechanism of GAA altering crystal growth is mainly to inhibit the growth of the (010) plane. A b-axis-oriented TS-1 zeolite enriched with hexa-coordinated Ti species displays better catalytic performance in the 1-hexene epoxidation reaction than the conventional TS-1 zeolite containing only framework Ti species (35 vs 24%). This can be ascribed to the more active hexa-coordinated Ti species and shorter diffusion distance. This synthetic strategy provides a way to change the zeolite morphology and tune the number and distribution of Ti species in TS-1 zeolites.