Synthesis of Si-LTA Zeolites with Controllable Defects in the Presence of Ammonia Fluoride 

Presenter

Taras Nagornyy

Campus

UMass Amherst

Sponsor

Wei Fan, Department of Chemical Engineering, UMass Amherst

Schedule

Session 4, 2:30 PM - 3:15 PM [Schedule by Time][Poster Grid for Time/Location]

Location

Poster Board A73, Campus Center Auditorium, Row 4 (A61-A80) [Poster Location Map]

Abstract

Replacement of hydrofluoric acid (HF) in the synthesis of siliceous and high-silica zeolites with less toxic agent is crucial for the improvement of zeolite synthesis safety and provide commercial availability. In this study, we have chosen to substitute HF with ammonia fluoride, NH₄F. NH₄F is less toxic than HF and much safer to handle during zeolite synthesis. NH₄F can provide essential roles of F^– in the Si-LTA synthesis including stabilizing double four-membered rings (D4Rs) of LTA zeolite and charge balancing the positive charges from the organic structure directing agents (OSDAs). Siliceous LTA zeolite was synthesized with 1,2-dimethyl-3-(4-methylbenzyl) imidazolium (BULKY) as the primary organic structure-directing agent (OSDA) using HF or NH₄F. The effect of tetramethyl ammonium (TMA) as the secondary OSDA also was studied. Under optimized synthesis conditions, we found it is feasible to synthesize defect-free Si-LTA using NH₄F. The number of defects in the as-made Si-LTA can be controlled by using TMA as the secondary OSDA in the presence of NH₄F.

We found that Si-LTA zeolite can be synthesized using NH₄F under basic conditions compared to the neutral conditions when HF was used. A fully crystalline Si-LTA sample can be obtained in as short as 6 hours in the presence of TMA (12 hours without), suggesting that the combination of TMA and NH₄F can give a faster rate of crystallization compared to the previous method. This will offer a new approach to control the defects in siliceous and high-silica zeolites. The control over the defects is crucial for zeolite adsorption and catalytic property, hydrophobicity. 

 

Keywords

Zeolite, Catalysis , DeNOx, LTA, Ammonia Fluoride

Research Area

Chemistry and Materials Science

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