HIGHLY POROUS HYBRID ZIRCONIUM PHOSPHONATES
BY NON-HYDROLYTIC SOL-GEL METHODS
Petr Machac1
, Ales Styskalik1
, Jiri Pinkas1
1
Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2,
CZ-61137 Brno, Czech Republic
ABSTRACT:
Organic-inorganic hybrid materials are attractive heterogeneous catalysts and catalyst supports.1
They combine the inorganic network stability with properties brought by the organic building blocks, i.e.,
controlled hydrophobicity, and improved hydrothermal stability. The combination of such a hybrid with
catalytically active metal may lead to successful catalyst material.2
Zirconium phosphonates are
promising Lewis acidic catalysts, but their conventional preparation (hydrothermal methods) yield
usually microporous layered structures.3
Non-hydrolytic sol-gel process can be applied to obtain
amorphous mesoporous 3D structures.4
We proposed a synthetic route to zirconium phosphonates based on the reaction of Zr
dialkylamides with trimethylsilyl phosphonates (eq. 1)2
with both terminal and bridging organic groups
(Me, t
Bu, Ph, ethylene, phenylene, xylylene). The nature of organic substituents in phosphonates played
a significant role in final product porosity. The surface area reached up to 700 m2
g-1
. Pore sizes were
usually in the mesoporous range (2.5 nm) even without templates. The degree of condensation ranged
from 65 to 85 %. Thus, there were still ~25 % of residual reactive groups on the xerogel surface available
for post-synthetic grafting.
Structure and acidity of zirconium phosphonates were thoroughly characterized by solid-state
NMR spectroscopy. The high atomic homogeneity was verified by IR spectroscopy and STEM-EDS.
The degree of condensation was determined gravimetrically and by TG-DSC. ICP-OES confirmed the
Zr:P ratios, which were ranging from 0.5 to 1. Catalytic activity of Zr sites was confirmed in a batch mode
on a model reaction: aminolysis of styrene oxide.
(eq. 1)
References
(1) Wight, A. P.; Davis, M. E.. Chem. Rev. 2002, 102 (10), 3589–3614.
(2) Machac, P.; Alauzun, J. G.; Styskalik, A.; Debecker, D. P.; Mutin, P. H.; Pinkas, J. Microporous Mesoporous Mater. 2021,
311, 110682.
(3) Taddei, M.; Sassi, P.; Costantino, F.; Vivani, R. Inorg. Chem. 2016, 55 (12), 6278–6285.
(4) Styskalik, A.; Skoda, D.; Barnes, C.; Pinkas, J. Catalysts 2017, 7 (6), 168.