Generating Beta Zeolite Nanosheets of Intergrown Polymorph B and C Using Polycationic Structure-Directing Agent

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Zeolitic nanosheets offer improved catalytic performance over bulk crystals due to enhanced mass transport and accessibility.
• Synthesizing Beta zeolite nanosheets, vital for industrial applications, remains challenging due to their inherent intergrowth nature.

Purpose of the Study:

• To develop a method for generating Beta zeolite nanosheets with a house-of-cards architecture.
• To investigate the structural and catalytic properties of these novel nanosheets.

Main Methods:

• Synthesis of aluminosilicate Beta nanosheets using a specific polycationic organic structure-directing agent (OSDA) in hydroxide media.
• Characterization using transmission electron microscopy (TEM), electron tomography, and 2D heteronuclear correlation NMR spectroscopy (2D 29Si{1H} and 27Al{1H} HCCH NMR).

Main Results:

• Successfully generated Beta zeolite nanosheets (approx. 16 nm thick) with a house-of-cards architecture and BEC topology, featuring straight micropore channels.
• NMR studies indicated strong interaction between framework aluminum and the OSDA within the channels.
• Enhanced catalytic activity, selectivity (ethylene, propylene), and lifetime in n-heptane cracking were observed, attributed to increased acidity and improved diffusion.
• The nanosheet architecture demonstrated robustness for further modifications like dealumination and Ti-incorporation, showing potential in cyclohexene epoxidation.

Conclusions:

• A novel method for synthesizing Beta zeolite nanosheets using a tailored polycationic OSDA has been established.
• The resulting Beta zeolite nanosheets exhibit superior catalytic performance in hydrocarbon cracking and epoxidation reactions.
• The design strategy for the OSDA and the synthesis protocol for Beta nanosheets hold promise for broader applications in catalysis.