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采用了恰当的衔接手法，层次清晰；文章用词灵活多样，高级词汇使用也比较准确；作者在句法层面做的很棒。
In our previous work [25], ZnBr2 supported on Fe3O4@MCM-41 was confirmed to be an effective and recoverable catalyst for the synthesis of SC in the presence of homogeneous quaternary ammonium salt. However, the optimal Zn loading reached up to 14.9 wt.%. Further supporting quaternary ammonium salt led to relatively low Fe3O4 and MCM-41 content but high active species content, giving impossibility in separation of supported catalyst simply by an external magnet and decrease in catalytic activity due to collapse in the support structure. Thus, the investigation on other catalyst was performed first herein. The results in Table 2 indicate that only 2.5 and 8.7% SC yield were obtained using Cu(acac)2 and n-Bu4NBr as catalyst alone (entries 1,2) while both the yield and the selectivity to SC was improved by using Cu(acac)2 and n-Bu4NBr as catalyst together although the SO conversion changed slightly (entry 3). It has been reported that the formation of SC depends on the activation of SO on the acidic sites while the activation of CO2 on the basic sites [37], respectively. The conversion of SO into SC includes the coordination of SO with metal center followed by the ring opening under the nucleophile attack of halide anion from quaternary ammonium salt [16,38]. The absence of Cu(acac)2 and/or n-Bu4NBr is supposed to be more helpful for the side reactions. As a result, relatively low selectivity was observed using Cu(acac)2 or n-Bu4NBr as catalyst alone. The GC-MS results confirm that the SC synthesis is accompanied by the formation of by-products such as phenylacetaldehyde, acetophenone and phenyl-1,2-ethanediol. The formation of phenylacetaldehyde and acetophenoneare ascribed to the Meinwald rearrangement of SO while the formation of phenyl-1,2-ethanediol is assigned to the hydrolysis of SO. The results in Table 2 show that the selectivity obtained in the presence of Cu(acac)2 was relatively lower than that of n-Bu4NBr. So we speculated that the side reactions such as Meinwald rearrangement and hydrolysis are more effectively prevented by the ring opening of SO. The catalytic performance of Cu(acac)2 and/or n-Bu4NBr supported on Fe3O4@MCM-41 was further tested. Surprisingly, both the SO conversion and the yield of SC were significantly improved (entries 4–9). It may be ascribed to three factors. Firstly, the mixed oxides support composed of Fe3O4 and MCM-41 may give a synergistic effect. The yield of SC obtained using Fe3O4 or MCM-41 as support alone (entries 4,5) was obviously lower than that observed in the presence of Fe3O4@MCM-41 (entry 6), confirming the synergistic effect derived from the mixed oxides support. Similar enhancement in the catalytic performance was also observed using binary Mg-Fe oxides as catalyst for the synthesis of ethyl methyl carbonate [39]. Secondly, epoxides could be activated by –OH groups contained in solid catalysts[40]. Thus the large number of accessible –OH groups on the surface of mixed support also gives positive effect on the catalytic performance. Finally, relatively high surface area of composed mixture is helpful for the dispersion of active species in the heterogeneous catalyst. The surface area of binary supported catalyst still reaches 332 m2/g even after anchoring Cu(acac)2 and n-Bu4NBr, as shown in Table 1. The results in Table 2 also reveal that the catalytic performance of supported n-Bu4NBr alone was lower than that of Cu(acac)2 (entries 7,8). It may be assigned to the possible interaction between Cu2 and hydroxyl or surface oxide species, which has been confirmed by XPS analysis (Figs. 5 and 6). The binary supported catalyst also displayed higher activity compared to that of n-Bu4NBr/Fe3O4@MCM-41 in the presence of homogeneous Cu(acac)2 (entries 4,6), giving a further explanation for the interaction between Cu2 and hydroxyl. It can also be seen from Table 2 that the binary supported catalyst displayed slightly poorer performance than that of supported Cu(acac)2 alone with identical Cu loading (entries 6,9). The overall loading of Cu and Br increased in binary supported catalyst although Cu loading kept constant. It may lead to the aggregation of active species and decrease in surface area, thus revealing negative effect on the reaction. The SC synthesis is mainly accompanied by the formation of phenylacetaldehyde as well as acetophenone via Meinwald rearrangement of SO [41]. The selectivity to SC at 92.2% obtained by supporting Cu(acac)2 alone was higher than that at 82.9% obtained previously by supporting ZnBr2 alone in the presence of homogeneous n-Bu4NBr [25], revealing the side reaction is easier to proceed in the presence of Lewis acid [42].
