(639b) Optimizing Hierarchical Zeolites for Applications in Catalysis

Maryam Khaleel^*, Rami Hamaidi,
Issam Ismail, Saeed Alhassan

*E-mail: maryam.khaleel@ku.ac.ae

Abstract

Efforts to overcome diffusional limitation in microporous
zeolites have been directed towards the design of hierarchical zeolite structures.
Hierarchical zeolites contain highly interconnected networks of zeolitic
micropores combined with meso- and/or macropores. Interest in these materials
stems from the higher reaction rates,^1,2
improved selectivity,³
resistance to deactivation,⁴
and novel adsorption behavior⁵
that they exhibit in comparison to the typical zeolites that only have micropores.
Among the synthesis approaches, repetitive branching by rotational intergrowth ^2,6–9
holds promise for industrial implementation due to its simplicity and lower
cost as it is a one-step synthesis which uses simple structure-directing agents
or additives compared to hard and dual-soft templating approaches.

As an
important component of fluid catalytic cracking (FCC) catalysts, Faujasite is
one of the most widely used zeolites. Hierarchical Faujasite grown in a house-of-card
assembly of nanosheets has been reported using either organosilane surfactants^7,9
or Lithium or zinc salts⁸.
Recently, we successfully prepared hierarchical Faujasite from sodium
aluminosilicate sols (fig. 1). However, the low framework Si/Al ratio renders
the framework unstable for ion exchange and catalytic applications.

Increasing the framework Si/Al ratio of synthetic Faujasite prepared from
inorganic sols has proven to be difficult. Recent work reported Si/Al ≈
2.2 for nano-sized Faujasite from inorganic sols.¹⁰
Higher Si/Al ratios require seeding, organic additives, or post synthetic
treatment with silicon tetrachloride or acid. In this work, we attempt to tune
the hierarchical Faujasite we synthesized for catalytic applications by
increasing the framework Si/Al ratio, while retaining the house-of-card
morphology, using both inorganic bottom up and post treatment approaches. The
synthesized materials will be converted to the protonated form to be tested for
n-butane cracking as a model system.

Figure 1: Hierarchical Faujasite prepared from sodium
aluminosilicate sols.

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