(96b) Combining Pre- and Post-Nucleation Trajectories for the Design of Hierarchical FAU/EMT Materials from Organic-Free Sols | AIChE

(96b) Combining Pre- and Post-Nucleation Trajectories for the Design of Hierarchical FAU/EMT Materials from Organic-Free Sols

Authors 

Gaber, D. - Presenter, The Petroleum Institute, Khalifa University of Science and Technology
Gaber, S. - Presenter, The Petroleum Institute, Khalifa University of Science and Technology
Khaleel, M. - Presenter, The Petroleum Institute, Khalifa University of Science and Technology
Ismail, I., Petroleum Institute, Khalifa University of Science and Technology
Alhassan, S., Khalifa University of Science and Technology. The Petroleum Institute

 

Efforts to overcome diffusional limitation in microporous
zeolites have been directed towards the design of hierarchical structures in
said zeolites. 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 intergrowth2,6Ð9 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. It consists of two
polymorphs: FAU (cubic) and EMT (hexagonal), which share the same periodic
building unit (PBU) known as the Faujasite sheet. The intergrowth of FAU and
EMT in the same material results in the development of hierarchical FAU/EMT
materials grown in a house-of-card assembly of nanosheets. Such materials have
been reported using either organosilane surfactants7,9 or Lithium or
zinc salts.8 However, both FAU and EMT can nucleate from inorganic
sols containing only sodium ions, hence, the development of a house-of-card
assembly of Faujasite sheets from sodium aluminosilicate mixtures is in
principle possible thus avoiding extra costs of additional additives.

Earlier findings by Khaleel et.al10 demonstrate the use of
pre- and post-nucleation trajectories in the synthesis of high FAU content
Faujasite nanocrystals. The aim of the present work
is to gain further insight and extend this principle into designing house-of-card
assembly of Faujasite nanosheets from organic-free sodium aluminosilicate sols.
The effect of combining different synthesis trajectories was investigated and
materials were characterized by high resolution transmission electron
microscopy and X-ray diffraction. Such materials are type X (Si/Al < 1.5) FAU/EMT
intergrowths that reduce the diffusion path length perpendicular to the sheets
(ca. 200 nm) and also provide extra meso/macro-porosity
between the sheets enhancing diffusion. Preliminary results indicate
that different hierarchal zeolite materials can be designed by proper
adjustment of the synthesis conditions. Findings demonstrate that it is
possible to combine the effects of pre-and post-nucleation sol composition to
steer crystal size and crystal structure, respectively. The initial sol
preserves the original trajectory towards large crystals after composition
change. Despite this memory effect, the sol at this stage is still agnostic
towards FAU or EMT formation, the relative content of which is dominantly
determined by the final composition. This expands the spectrum of hierarchical
materials that can be designed. After optimizing the
hierarchal zeolite structure, the performance of the prepared materials can be
tested in catalytic applications such as n-butane cracking



References

 

(1)      van Donk, S.;
Broersma, A.; Gijzeman, O. L. .; van Bokhoven, J. .; Bitter, J. .; de Jong, K.
. J. Catal. 2001, 204 (2), 272Ð280.

(2)      Zhang, X.;
Liu, D.; Xu, D.; Asahina, S.; Cychosz, K. A.; Agrawal, K. V.; Wahedi, Y. Al;
Bhan, A.; Hashimi, S. Al; Terasaki, O.; Thommes, M.; Tsapatsis, M. Science
(80-. ).
2012, 336 (6089), 1684Ð1687.

(3)      Christensen,
C. H.; Johannsen, K.; Schmidt, I.; Christensen, C. H. J. Am. Chem. Soc. 2003,
125 (44), 13370Ð13371.

(4)      Choi, M.; Na,
K.; Kim, J.; Sakamoto, Y.; Terasaki, O.; Ryoo, R. Nature 2009, 461
(7261), 246Ð249.

(5)      Xu, D.;
Swindlehurst, G. R.; Wu, H.; Olson, D. H.; Zhang, X.; Tsapatsis, M. Adv.
Funct. Mater.
2014, 24 (2), 201Ð208.

(6)      Chaikittisilp,
W.; Suzuki, Y.; Mukti, R. R.; Suzuki, T.; Sugita, K.; Itabashi, K.; Shimojima,
A.; Okubo, T. Angew. Chemie Int. Ed. 2013, 52 (12),
3355Ð3359.

(7)      Inayat, A.;
Knoke, I.; Spiecker, E.; Schwieger, W. Angew. Chemie Int. Ed. 2012,
51 (8), 1962Ð1965.

(8)      Inayat, A.;
Schneider, C.; Schwieger, W. Chem. Commun. 2015, 51 (2),
279Ð281.

(9)      Khaleel, M.;
Wagner, A. J.; Mkhoyan, K. A.; Tsapatsis, M. Angew. Chemie - Int. Ed. 2014,
53 (36), 9456Ð9461.

(10)    Khaleel, M.; Xu, W.;
Lesch, D. A.; Tsapatsis, M. Chem. Mater. 2016, 28 (12),
4204Ð4213.