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

能够很好的使用长难句且句法很棒；语句间的衔接成分用的不错，同时文章中的过程性词汇很丰富；作者词汇表达较多样灵活，也能较准确地使用高级词汇。

A binary supported catalyst was developed by supporting Cu(acac)2 as well as n-Bu4NBr on Fe3O4@MCM-41 and employed as catalyst for the synthesis of SC via the coupling reaction of SO with CO2. The XRD analysis reveals no obvious change in the structure of the complex support after the introduction of Cu(acac)2 and n-Bu4NBr but with decrease in the order of hexagonal mesoporous. Most Cu(acac)2 possibly dispersed inside the framework while n-Bu4NBr mainly on the surface of the support. The activity of binary supported catalyst depended on supporting Cu(acac)2 and n-Bu4NBr alone or together, molar ratio of materials and reaction conditions including CO2 pressure, reaction temperature and time. SC yield at 87.5% was obtained under 8 MPa at 100 oC for 1 h, which is close to that given in homogeneous catalytic system reported previously. The binary supported catalyst was simply recovered by a permanent magnet after the reaction and reused without further treatment. No significant loss in the activity was observed at the initial 3 cycles. The AAS and IC analysis revealed that Cu loading almost kept constant while Br loading decreased obviously after the third run. The catalytic performance of the recovered catalyst can be enhanced by supplementing moderate amount of n-Bu4NBr after the third run.