Considering that the USY and H-Beta are important zeolites catalysts [
7], and Amberlyst-15 is a typically commercial acidic resin catalyst [
14], therefore, their catalytic activities in the acetalization were also tested and compared with those of MIL-100(Fe) and MIL-100(Fe)@SiO
2@Fe
3O
4, and the results are shown in Fig. 7. Among the catalysts investigated, the fresh Amberlyst-15 showed a highest activity on a weight basis. The high catalytic activity of Amberlyst-15 can probably be attributed to its high number of acid sites available (4.7 mmol·g
-1, Table 1), which is much higher than those of the other catalysts. In contrast, the USY and H-Beta catalysts showed comparably lower catalytic activities which is probably due to intracrystalline diffusion limitations [
8]. On the other hand, it is interesting to noted that catalytic activity over MIL-100(Fe)@SiO
2@Fe
3O
4 was almost the same with that of MIL-100(Fe). Considering that the low density of the parent MIL-100(Fe) (close to 1 g/cm
3) [
13], easily resulting in inconvenient separation from liquid medium when used as a heterogeneous catalyst. Thus, the developed MIL-100(Fe)@SiO
2@Fe
3O
4 may have the advantages of convenient recycling and reuse.