Encapsulated Non-Exchangeable Na⁺ Ions Determining the Upper Limit of Al Inclusion in FAU-A Multiscale Simulation

Area of Science:

• Materials Science
• Catalysis
• Computational Chemistry

Background:

• Y-zeolite's properties are tunable by controlling aluminum distribution.
• The charge-balancing agent significantly affects framework structure and acidity.
• Understanding aluminum siting is crucial for optimizing zeolite performance.

Purpose of the Study:

• Investigate the role of Na+ as a charge-balancing agent in Y-zeolite.
• Determine how Na+ influences aluminum atom distribution and acid site strength.
• Correlate structural changes with catalytic activity in propane cracking.

Main Methods:

• Density Functional Theory (DFT) computations.
• Machine learning descriptors.
• Ab initio molecular dynamics (AIMD) simulations.
• Experimental analysis (e.g., adsorption studies).

Main Results:

• Na+ ions promote larger Al-Al separations (4N-Al, 5N-Al) compared to H+ (3N-Al).
• Na+ preferentially occupies specific sites: six-membered ring (6MR) > double six-membered ring (D6R) > four-membered ring (4MR).
• Thermodynamically favorable limit for Y-zeolite synthesis suggests low Si/Al ratios (≤ 3).
• Na+-containing Y-zeolite exhibits enhanced acid strength and higher catalytic activity in propane cracking.

Conclusions:

• Na+ ion's influence on Al distribution is key to understanding Y-zeolite structure-property relationships.
• The findings explain challenges in synthesizing high Si/Al ratio Y-zeolites.
• Na+-modified Y-zeolites show promise for improved catalytic applications.