Thermogravimetry (TG) and differential thermal analysis (DTA)
of the sample were employed to clarify the thermal stability of the
grafted ionic liquid. As shown in Fig. 7, gradual weight loss was
observed from about 50 8C to approximately 600 8C, with three main loss weight peaks. The first peak involved in the outer layer
water desorption; the second peak accounted for decomposition of
GILs; and the last one could be assigned to condensation of silanol
group. It can be seen that the sample was stable under 250 8C.
In the present work, the catalytic performance of catalysts was
investigated under the identical conditions (see Table 3). Grafted
ionic liquids [Amim]OH/SiO2 possessed the best catalytic performance.
A series of catalytic cycles were conducted to investigate the
reusability of the catalyst. In each cycle, the catalyst was separated
by simple filtration and then used for the next reaction directly.
The results listed in Table 4 indicated that the catalyst could be
reused for up to four times.