(101b) Organic-Free Route for the Synthesis of Hierarchical Zeolite ZSM-11 Catalysts

Organic-Free Route for the Synthesis of Hierarchical Zeolite ZSM-11
Catalysts

Rishabh Jain¹, Aseem
Chawla¹, Noemi Linares², Javier Garcia-Martinez²
and Jeffrey D. Rimer¹

¹Department of Chemical and Biomolecular
Engineering, University of Houston, Houston, Texas

²Molecular
Nanotechnology Lab, Department of Inorganic Chemistry, University of Alicante,
Alicante, Spain

Zeolites consist of a three-dimensional
network of micropore channels (typically <1 nm).
Although small pores are essential for shape selectity
in chemical reactions, they often impart mass transport limitations and restrict
the transport of bulky molecules, thereby limiting their access to active sites
witin the interior of the catalyst. Mass transport
limitations are accentuated by long diffusion path length, which can be reduced
by either introducing mesopores in the micropore channel system (so-called hierarchical zeolites)
or by reducing the crystal size to nanoscale dimensions (< 100 nm).¹

Among these approaches,
hierarchical zeolites possessing mesopores in addition to the inherent
micropores have garnered significant interest.² Hierarchical
zeolites display improved performance in a variety of catalytic processes
including alkylation, transalkylation, isomerization,
cracking, methanol to hydrocarbon (MTH), and condensation reactions;³
however, the majority of reported approaches to design hierarchical zeolites
employ complex and/or expensive organics, which could limit their use at
industrial scale, specially if they need to be
removed by calcination.⁴ An alternative approach is seed-assisted
zeolite growth, which is a facile method to reduce (or eliminate) organics in
zeolite synthesis.⁵ Seeding also reduces the crystallization time
and can alter the physicochemical properties of the final product; however, the
exact mechanism of seed-assisted zeolite crystallization remains elusive.

Here, we present a unique
approach to synthesize hierarchical ZSM-11 (MEL framework) with intergrown nanosheets using a
seed-assisted route in organic-free media. To the best of our knowledge, this
is the first example of such a complex morphology for a MEL-type zeolite
synthesized in the absences of organic structure-directing agents. A recent
study by our group has shown that the reduction in HZSM-11 crystal size from
750 to 150 nm significantly extends the time-on-stream (TOS) lifetime in MTH
reactions.⁶ Ongoing tests of hierarchical HZSM-11 catalysts prepared
with a range of properties (e.g., crystal size and Si/Al ratio) are being
conducted with the long-term goal to develop more generalized
structure-performance relationships in zeolite catalysis.

(1)  
Mintova et al.; Comptes Rendus Chimie 19 (2016) 183-191.

(2)  
Li E.,  García-Martínez J., (ed.) Mesoporous Zeolites:
Preparation, Characterization and Applications. WILEY-VCH (2015).

(3)  
Holm et al.; Catal. Today 168 (2011) 3-16.

(4)  
a) Choi et al.; Nature 461 (2009) 246-249, b) Zhang et al.; Science (2012)
1684-1687.

(5)  
Ji et al.; Comment. Inorg.
Chem. 36 (2016) 1-16.

(6)  
Shen et al.; ACS Catal. (2018) 11042-11053.