Two-dimensional Organic-Inorganic Ti-MWW as Regenerable Catalyst for Fixed-bed Propylene Epoxidation

The direct epoxidation of propylene to propylene oxide with hydrogen peroxide, known as the HPPO process, is a highly efficient and eco-friendly route for propylene oxide production. In the present study, the three-dimensional (3D) MWW-type titanosilicate Ti-MWW in shaped form was reconstructed to a 2D organic-inorganic hybrid material through the hydrothermal treatment of piperidine (PI) solution, which serves as a highly active catalyst for the fixed-bed HPPO process. The PI hydrothermal treatment induced chemical modifications on the Ti active centers, fabricating an open hexacoordinated Ti species [Ti(OSi)₂(OH)₂(H₂O)PI], which significantly enhanced the catalytic activity. The solvent effect was also altered after the PI hydrothermal treatment, especially for methanol. In the continuous fixed-bed HPPO reaction, this 2D organic-inorganic Ti-MWW catalyst (RS-Ti-MWW) exhibited exceptional stability, achieving a lifetime of 730 h in MeCN and 216 h in MeOH, with PO selectivity exceeding 99.6% and H₂O₂ utilization above 95%. RS-Ti-MWW can be regenerated through calcination and the subsequent hydrothermal treatment of PI solution, and the regenerated sample remains stable for up to 730 h of continuous operation, demonstrating its strong potential for industrial application.