Presentation title:

Synthesis of porous inorganic matrices by nonhydrolytic sol-gel methods

Petr Machac,^1 Ales Styskalik,^1 Zdenek Moravec,^1 Jiri Pinkas^1

^1 Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, 61137 Brno, Czech
                                             Republic

Abstract

Catalysts play a crucial role in meeting increasingly stringent ecological demands. They also
reduce the costs in the industrial sector, enabling chemical processes by lowering the activation
energy and enhancing economic viability. However, many of the catalysts currently employed in the
industry are simple inorganic systems with poorly characterized mechanisms of action, limiting
their development. Additionally, these catalysts often suffer from heterogeneity and phase
separation issues.^1

Conventional synthesis methods for heterogeneous catalysts typically yield crystalline materials
with microporosity (<2 nm), which disallow to transform bulky organic substrates.^2 The
nonhydrolytic sol-gel approach allows the production of kinetically amorphous products with
mesoporosity (2-50 nm). The use of nonhydrolytic sol-gel synthesis also improves the homogeneity of
mixed oxides.^3

Our research is focused on synthesis of heterogenous catalysts with tunable properties.  Thanks to
the organic-inorganic hybrid character of final material we can control the porosity or influence
the hydrophobicity, figure 1. Three major groups of materials were investigated, aluminum
phosphonates, zirconium phosphonates and zirconium silicates. The aluminum centers act as small and
hard Lewis acid while the zirconium centers exhibit softer behavior.^4,5 This determines their
application as acid/base catalysts. However, due to variations in the active sites (such as
geometry and coordination number), selectivity may be compromised.  The possibility of synthesis of
well-defined zirconium sites in silica was explored to avoid this issue. The zirconium centers were
built by bottom-up methods from molecules.  Each zirconium atom is covalently bonded to 2, 3 or 4
bulky and rigid silicate molecules which ensure the uniformity of active sites. To evaluate their
activity, all materials were tested in model catalytic reactions.

Figure 1 The TEM image of porous structure of xerogel (left) and surface areas of
zirconophosphonates (right)

Acknowledgement

The work has been financially supported by the Czech Science Foundation under the project
GJ20-03636Y and by the Grant Agency of Masaryk University under grant project number
MUNI/J/0007/2021.

References

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(5)        Hradsky, D.; Machac, P.; Skoda, D.; Leonova, L.; Sazama, P.; Pastvova, J.; Kaucky, D.;
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