(101c) Additive-Free Synthesis of Hierarchical Zeolites By Utilizing Aluminosilicate Gel Memory

Additive-free
Synthesis of Hierarchical Zeolites by Utilizing Aluminosilicate Gel Memory

Safiya Khalil,¹ and Maryam Khaleel ^1,2,*

¹ Department of Chemical Engineering,
Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates

² Center for Catalysis and
Separation (CeCaS) and Research and Innovation Center on CO₂ and H₂
(RICH), Khalifa University of Science and Technology, Abu Dhabi, United Arab
Emirates

*Corresponding author: maryam.khaleel@ku.ac.ae

Efforts to overcome diffusional limitation in microporous zeolites
have been directed towards the design of hierarchical zeolite structures.
Interest in these materials stems from the higher reaction rates, improved
selectivity, resistance to deactivation, and novel adsorption behavior that
they exhibit in comparison to the typical zeolites that only have micropores. Faujasite
and LTA are two zeolites that are widely used in industry.

Hierarchical Faujasite has been prepared by post synthetic
treatment, or by using soft-templates or hard templates, adding extra cost and
complexity to the synthesis. House-of-card assembly of Faujasite sheets by
repetitive branching has been previously reported using either organosilane
surfactants¹ or lithium or zinc salts.² Previous work by Khaleel et. al.³ showed that FAU/EMT intergrowth is
responsible for the repetitive branching leading to the development of
house-of-card assembly of zeolite X nanosheets. Thus, being able to control the
intergrowth of crystal phases in particles will allow control of mesopore size
by controlling sheet thickness and branching frequency. House-of-card assembly of Faujasite nanosheets was synthesized
solely from inorganic sodium aluminosilicate solution following earlier
findings by Khaleel et. al.⁴ demonstrating the use of pre- and
post-nucleation trajectories for the synthesis of high FAU content Faujasite
nanocrystals (Fig. 1a).⁵ Nano-sized
LTA is also usually synthesized by using a large amount of organic additives.
In this work we attempt to synthesized nano-sized LTA from inorganic sodium
aluminosilicate sols by utilizing the gel memory effect to combine different
synthesis trajectories (Fig. 1b). The effect of morphology on the material
properties and activity is tested, to give better insight into property
tunability.

Figure 1. a) Hierarchical house-of-card
Faujasite synthesized from inorganic sodium aluminosilicate sols. b) Nano-sized
LTA synthesized from inorganic sodium aluminosilicate sols.

The results of this work demonstrate that the pool of accessible
zeolite morphologies can be expanded beyond those possible from direct
synthesis, by utilizing the gel memory effect to combine different synthesis
trajectories.

References

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