(129d) Effects of Zeolite Growth Modifiers on Different Stages of ZSM-5 Crystallization

Effects
of Zeolite Growth Modifiers on Different Stages of ZSM-5 Crystallization

Wei Qin and Jeffrey D. Rimer

Chemical and Biomolecular Engineering,
University of Houston, 4726 Calhoun Rd., Houston, Texas 77204 USA

Zeolite ZSM-5 is a common heterogeneous catalyst in
refinery and petrochemical processes, owing to its excellent shape-selectivity,
strong Brønsted acidity, and high thermal/hydrothermal stability. It has an MFI
structure with 3-dimensional pores consisting of interconnecting straight and
sinusoidal channels. Molecular diffusion is much faster in the straight
channels oriented along the [010] direction. To this end, it is desirable to
selectively control the [010] thickness of ZSM-5 crystals.

Here, we will present a novel approach to tailor ZSM-5 morphology
that incorporates zeolite growth modifiers (ZGMs). The use of ZGMs has proven
to be an efficient method to tailor the morphology of silicalite-1, which is the
siliceous isostructural analogue of ZSM-5.¹ For
our study of ZSM-5 synthesis in the presence of ZGMs, we assessed a library of
modifiers previously screened for slicalite-1 to determine the influence of
aluminum incorporation within the MFI framework. It was observed that subtle
changes in the synthesis conditions can alter ZGM binding specificity to
different crystallographic faces of ZSM-5. Using atomic force microscopy (AFM),
we show that chemical force microscopy can be used to efficiently probe
modifier-crystal interactions in order to elucidate ZGM molecular recognition
for different zeolite surfaces.²

We also investigated the effects of ZGMs on the
initial stages of amorphous precursor self-assembly and evolution
(pre-nucleation) as well as crystal growth using a combination of two
techniques: small angle X-ray scattering (SAXS) ³ and dynamic light
scattering (DLS). We observed that polycations have a unique effect of
promoting precursor aggregation during the induction period.

Through the judicious selection of ZGMs under
different synthesis conditions, we were able to synthesize ZSM-5 crystals with
various sizes and morphologies. We will present details of these syntheses as
well as catalytic tests of ZSM-5 catalysts with a model reaction to gain a
better understanding of the relationship between ZSM-5 morphology and catalyst
performance. Collectively, this work provides quantitative guidelines for
designing synthesis protocols to tailor ZSM-5 crystallization and improve
catalyst properties for a wide range of applications.

(1) Lupulescu, A. I.; Rimer, J. D. Angew. Chemie -
Int. Ed. 2012, 51 (14), 3345–3349.

(2) Lupulescu, A. I.;
Rimer, J. D. Science. 2014, 729.

(3)  Fedekyo, J.; Rimer, J.
D.; Lobo, R. et al. J. Physical Chemistry C. 2004, 108.