<div>
<p>Herein, we
present novel phenylene- and xylylene-bridged silica and metallosilicate materials
prepared by non-hydrolytic sol-gel. The hybrid silica are highly porous, chemically
similar to periodic mesoporous organosilica (PMO), but amorphous. Analogous
hybrid metallosilicates are obtained by directly incorporating Al, Nb, or Sn in
the hybrid silica framework. Exhibiting open texture, surface acidity and
tunable hydrophobicity, these materials are excellent candidates for catalytic
alcohol dehydration reactions. The gas-phase hydrothermal and thermal stability
of these materials is examined. While the hybrid silica is expectedly stable, a
stark decrease in stability is observed for phenylene bridged silsesquioxanes upon
metal introduction. The extent of the hydrolytic Si−C(sp<sup>2</sup>) bond
cleavage is quantitatively followed by <sup>29</sup>Si MAS NMR, TG analysis,
and GC-FID analysis of effluent coming from samples exposed to water vapor. Two
important features affecting the hydrothermal and thermal stability are
identified: (i) the homogeneity of metal dispersion within the silica matrix,
and (ii) the electronegativity of the incorporated metal. The stability of
hybrid metallosilicates is significantly improved by replacing the phenylene
bridges with xylylene bridges, due to the presence of more stable Si−C(sp<sup>3</sup>)
bonds. Interestingly, the latter hybrid metallosilicate proves to be an active catalyst
for the dehydration of ethanol to ethylene. Unlike the other hybrid materials
presented here, it reaches high ethylene yields without undergoing degradation
and deactivation.</p>
</div>
Porous Silicates Modified with Zirconium Oxide and Sulfate Ions for Alcohol Dehydration Reactions