Synthesis and Characterization of Tin, Tin-Aluminum, and Tin-Boron Containing MFI Zeolites

Shahami, M., Tulane University
Ransom, R., Tulane University
Shantz, D. F., Tulane University

Graphical Abstract:

Zeolites are an
intellectually fascinating and
technologically important class of materials used
in the
chemical conversion and separation of small molecules. Their ability to
achieve these unit operations is a
result of the crystalline microporous structures enabling highly size-selective separations.[1] Coupling
that with the ability to impart acidity to the zeolites through the introduction of trivalent elements such as aluminum and boron into the framework has led to zeolites finding a wide range of applications in the chemical and
petrochemical industry.[2] Over the last 20-30
years beyond aluminum and boron,
has been
shown that other elements including titanium[3], tin[4] and germanium[5] can
be introduced into the zeolite
lattice with varying
levels of success. This expansion of the zeolite framework composition space has led
to new uses for zeolites
a range of catalytic chemistries.

The synthesis and characterization of tin, tin/aluminum, and tin/boron containing MFI zeolites will be presented. It is shown that tin uptake is high (near 100%) and decreases with
the introduction of a second
heteroatom. Also, the boron uptake was found to be low for tin-boron-MFI samples, consistent with our
prior work on germanium-boron-MFI[6]. XRD and
FE-SEM show that higher tin contents and higher aluminum and boron contents in the synthesis gel lead to smaller and less faceted crystals. Diffuse reflectance UV-Vis spectroscopy confirms the tetrahedral framework coordination of tin within the zeolite
no polymeric SnO2 can be detected, given the absence of a strong signal at 280
nm. XPS,
with UV-Vis, indicates the absence of an additional phase in the surface of these particles. In-Situ IR
spectroscopy, using methanol as a probe molecule, shows that the nature of number of acid
sites in
these materials changes in going from pure tin-MFI (very weakly acidic) to tin-aluminum-MFI (mildly acidic).
Lewis acid nature of the tin
was confirmed using
of d-acetonitrile treated samples.

Keywords: Tin-MFI, synthesis, probe molecule binding, mixed heteroatom zeolites


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(5)  Z. Gabelica, J.L. Guth, A Silicogermanate with a Si/Ge Ratio Greater Than or Equal to
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(6)  Vargas,
Nataly Garcia, Scott Stevenson,
and Daniel F. Shantz. "Simultaneous isomorphous incorporation of boron
and germanium in
MFI zeolites." Microporous and
Mesoporous Materials
170 (2013): 131-140.


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