. The results are displayed inFig. 6. The poorest performance was observed with
polymax, leading to a drastic declining of activity after 4 h onstream. The fast deactivation of polymax could be due to the loss
of acidity from the catalyst surface by the water produced during
the reaction. In contrast, the catalyst of Amberlyst Wet, Zeolite,
or Amberlyst Dry exhibited superb stability over a long time-onstream, producing solketal at a high yield >70% during the whole
course of the experiments for up to 24 h on-stream, although it
is clear that these catalysts, except polymax, exhibited only a slight
decrease in activity with increasing time on-stream. To understand
the superb stability of the Amberlyst Wet catalyst, the textual
properties and acidity for its spent catalyst after 24 h time-onstream were measured, and the results are presented comparatively against those of its fresh catalyst inTable 4. In addition, FTIR
measurements of the fresh and spent catalyst of Amberlyst Wet
after 24 h time-on-stream were measured and the spectra are displayed inFig. 7. As shown in Table 4andFig. 7, it is apparently that
the Amberlyst Wet catalyst did not deteriorate significantly in its
textual properties (specific surface area and pore structure) during
the experiments for 24 h on-stream, which explains its superb stability for the reaction. However, fromTable 4, the acidity of the
Amberlyst Wet catalyst did decrease slightly from 5.6 eq/g for
the fresh catalyst to 5.2 eq/g for the spent catalyst, which might account for the slight deactivation of the catalyst during the experiments for 24 h on-stream