<p>Ethanol dehydration is
effectively catalyzed by solid acids, such as HZSM-5,
alumina, or silica-alumina. In these catalysts, the amount, nature, and
strength of acid sites is believed to determine catalyst activity and
stability. However, surface hydrophilicity or hydrophobicity can
be suggested as another decisive catalyst property that can directly influence
performance. For example, a more hydrophobic surface might be beneficial in repelling
the co-product of the reaction, water. However, these aspects have been studied
only scarcely in the context of alcohol dehydration. Here, a series of mesoporous hybrid aluminosilicate catalysts containing CH<sub>3</sub>Si
groups was prepared in
one pot by non-hydrolytic sol-gel (NHSG). The presence
of the methyl groups was verified by IR, solid-state NMR, and ToF-SIMS. Aluminum
is mostly incorporated in tetrahedral coordination in the hybrid silica matrix.
Two parameters were varied: (i) the Si:Al ratio and (ii) the Si:MeSi ratio. On
the one hand, changing the Si:Al ratio had a marked impact on hydrophilicity,
as attested by water sorption measurements. On the other hand, unexpectedly,
the introduction of methyl groups had no clear influence on sample
hydrophilicity. Nevertheless, some of the methylated aluminosilicate catalysts
markedly outperformed the purely inorganic catalysts and a commercial
silica-alumina benchmark. While a direct influence of surface hydrophilicity or
hydrophobicity could be excluded, characterization of acidity (IR-pyridine) revealed that these improved
performances are correlated with a modification of the acidic properties in the hybrid catalysts caused by the presence of methyl groups. A decisive role of acidity in ethanol dehydration was confirmed by an
experiment with delayed addition of the Al precursor in the NHSG synthesis.
This led to a higher Al surface concentration, marked acid sites number increase,
and better catalytic performance, even competing with HZSM-5 in terms of
activity.</p>