Regulating Titanium Species on TS-1 Zeolites by Na+ for Liquid-Phase Epoxidation of Propylene and H2O2

This paper focuses on the hydrothermal modification of as-synthesized TS-1 zeolites with Na⁺ ion-containing TPAOH solutions. The effects of NaNO₃ dosage, TPAOH concentration, and modification time are investigated in detail. Multiple techniques including XRD, XRF, transmission electron microscopy, Ar physisorption, FT-IR (skeletal vibration and hydroxyl stretching), UV–vis, and UV–Raman (excited by 257 and 266 nm laser lines, respectively) are employed to characterize the parent zeolites and their modified catalyst samples, with emphasis on revealing the changes of both the microenvironment and coordination state of titanium species in the modified zeolites. Besides, propylene and H₂O₂ liquid-phase epoxidation is used as a probe reaction to evaluate the catalytic performance of the modified catalysts, which is carried out in both the batch reactor and fixed-bed reactor. Results show that the hydrothermal modification of the TS-1 zeolite with a Na⁺ ion-containing TPAOH solution is a very useful method to simultaneously regulate the microenvironment and coordination state of titanium species as well as the diffusivity of the micropore in the TS-1 zeolite and, therefore, to remarkably improve its selectivity and catalytic activity.