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采用了适当的衔接手法，层次清晰；作者高级词汇使用比较准确，词汇表达较丰富，但仍需增加词汇积累；复杂句使用不错，句法规范。
It has been confirmed that the SC synthesis significantly depends on the molar ratio of quaternary ammonium salt to metal center, and an optimum molar ratio of metal center to 2 equiv. of quaternary ammonium salt is generally required [16,38]. So the SC synthesis was carried out with a molar ratio of Cu(acac)2 to n-Bu4NBr at 1:2. The results in Table 3 reveal that both the conversion of SO and the yield of SC were related to the amount of catalyst employed (entries 1–6). The yield of SC firstly increased and then decreased with increase in the amount of Cu(acac)2 as well as n-Bu4NBr. It can be ascribed to increase in active species by enhancing the amount of catalyst when the molar ratio of Cu(acac)2 to SO was relatively low. It has been reported that the reactions performed in supercritical CO2 generally proceed in the liquid phase mainly composed of CO2 phase [43]. The amount of support increased more markedly with increasing the amount of heterogeneous catalyst due to relatively low content of active species including Cu2 and Br-. It may result in insufficient contact among catalyst, CO2 and substrate in liquid phase in the presence of excessive amount of heterogeneous catalyst. As a result, excessive amount of catalyst gives a negative effect on the reaction, and drop in the conversion of SO and the yield of SC were observed (entry 7). For example, the yield of SC dropped to 76.3% once the molar ratio of Cu(acac)2 to SO was elevated to 1:50 (entry 7). Table 3 shows that SC yield at 87.1% and selectivity at 89.1% were given in the presence of binary supported catalyst. It is only slightly lower than 91.7% yield of SC obtained using Cu(acac)2/Fe3O4@MCM-41 and homogeneous n-Bu4NBr as catalyst together. So it is reasonable to conclude that the binary catalyst is also effective for the SC synthesis.
