HYBRID ACID CATALYSTS PREPARED VIA TRIMETHYLSILYLATION OF ALUMINOSILICATES SYNTHESIZED BY
NON-HYDROLYTIC SOL-GEL

Lucie Leonova^1, Petr Sazama^2, Jana Pastvova^2, Jiri Pinkas^1, Ales Styskalik^1

1 Masaryk University, Department of Chemistry, Brno, Czech Republic, (corresponding author:
styskalik@chemi.muni.cz)

^2J. Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences, Prague, Czech Republic

Hybrid materials based on aluminosilicates are extensively studied for their enhanced catalytic
performance. Organic groups can change acidity, hydrothermal stability, and porosity. First, we
have shown, that non-hydrolytic sol-gel (NHSG) provides highly homogeneous and porous
aluminosilicate materials exhibiting superior activity and long-term stability in ethanol
dehydration [1]. Second, the ethylene selectivity was improved by one‑pot incorporation of organic
groups [2]. Interestingly, this approach did not display the direct influence of hydrophobicity on
alcohol dehydration in contrary to other reports [3].

In this study, the NHSG-prepared aluminosilicate catalysts (fully inorganic) were
post‑synthetically modified by grafting trimethylsilyl groups onto their surfaces. Trimethylsilyl
groups were attached to the surface using trimethylchlorosilane or trimethyl(methoxy)silane. The
number of reacted ≡Si−OH moieties and thus the trimethylsilyl groups loading was controlled via
a temperature‑vacuum pretreatment of aluminosilicate samples. Trimethylsilyl groups loading was
evaluated by ^29Si MAS NMR measurements (Figure 1). Structure, porosity, acidity, and
hydrophobicity of NHSG‑prepared catalysts were closely followed by MAS NMR studies, N[2]
physisorption, IR-pyridine analyses, and water adsorption. Moreover, aluminosilicates were tested
in a gas-phase fixed-bed catalytic reactor in ethanol dehydration and in a batch reactor in
aminolysis of styrene oxide (liquid phase). These tailored NHSG-prepared aluminosilicate catalysts
exhibited varying catalytic activity and selectivity in both catalytic reactions depending on
trimethylsilyl groups loading in the samples.



    Figure 1: Comparison of pristine aluminosilicate with post-modified aluminosilicate samples
                                         in ^29Si MAS NMR


References

[1]        A. Styskalik, V. Vykoukal, L. Fusaro, C. Aprile and D. P. Debecker, Appl. Catal. B
Environ., 2020, 271, 118926.

[2]        A. Styskalik, I. Kordoghli, C. Poleunis, A. Delcorte, Z. Moravec, L. Simonikova, V.
Kanicky, C. Aprile, L. Fusaro and D. P. Debecker, J. Mater. Chem. A, 2020, 8, 23526–23542.

[3]        R. van Grieken, J. A. Melero and G. Morales, J. Mol. Catal. A Chem., 2006, 256, 29–36.


The work has been financially supported by the Czech Science Foundation under the project
GJ20-03636Y.