2014年6月英语四级作文真题附范文(第2套):A Beautiful City in China

作者能较熟练地使用词汇表达，一些高级词汇的使用也比较灵活；作者在句法层面做的很棒；全文结构较为严谨。

The theoretic mass ratio of Cu to Br is 1:2.54 for Cu(acac)2/n-Bu4NBr/Fe3O4@MCM-41 with 2.4 wt.% Cu and 6.1 wt.% Br loading. However, 1:22.9 mass ratio of Cu to Br can be calculated according to the surface composition obtained by XPS analysis, in which 0.07 wt.% Cu and 1.6 wt.% Br are detected on the surface of supported catalyst. It is far lower than that of the mass ratio of Cu to Br in the catalyst determined by AAS and IC. These results further reveal that Cu(acac)2 mainly enters into the framework of MCM-41 while considerable amount of n-Bu4NBr disperses on the support surface, explaining the observation of the characteristic peaks of n-Bu4NBr in the supported catalyst with relatively higher loading, as shown in Fig. 3.