Hierarchical Ti-MWW for Efficient Propylene Epoxidation With Cumene Hydroperoxide

Area of Science:

• Materials Science
• Catalysis
• Chemical Engineering

Background:

• Diffusion limitations hinder epoxidation reactions with large molecules using conventional catalysts.
• Titanium-silicate (Ti-MWW) zeolites are promising catalysts but face challenges with accessibility.

Purpose of the Study:

• To synthesize hierarchical micro-mesoporous Ti-MWW zeolites to improve catalytic performance in epoxidation.
• To overcome diffusion limitations for large molecules in propylene epoxidation.

Main Methods:

• A one-pot dissolution-recrystallization process was employed to create Ti-MWW zeolites with hierarchical structures.
• Characterization of pore structure, Ti site distribution, and catalytic activity was performed.
• Poisoning experiments were conducted to determine active site location.

Main Results:

• The synthesized hierarchical Ti-MWW exhibited bimodal pores and abundant external Ti sites.
• Propylene epoxidation achieved a high propylene oxide (PO) yield of 91%, significantly outperforming pristine Ti-MWW (35%).
• Poisoning studies indicated the reaction primarily occurs on the external surface of the catalyst.

Conclusions:

• The hierarchical structure and accessible external Ti sites are crucial for high epoxidation activity.
• Recrystallization enhances open Ti sites, boosting catalytic efficiency.
• The robust Ti-MWW framework offers superior stability under harsh reaction conditions compared to other mesoporous catalysts.