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

句法方面做得很棒，但是从句不多；文章词汇表达丰富，高级词汇积累做的也很棒；文章层次较为清晰。

Coupling reaction of supercritical carbon dioxide with styrene epoxide over Cu(acac)2 and n-Bu4NBr supported on Fe3O4@MCM-41 Guo-Zhi Fan*, Shan-Shan Luo, Jun-Tao Yan, Guang-SenSong, Jian-Fen Li* School of Chemical and Environmental Engineering, Wuhan Polytechnic University, Wuhan 430023, China ABSTRACT Much attention has been paid to the conversion of carbon dioxide (CO2) into chemicals recently, in which catalyst plays a key role due to inertnessnature of CO2. In this work, Cu(acac)2/n-Bu4NBr/Fe3O4@MCM-41was prepared by supporting Cu(acac)2 as well as n-Bu4NBr on complex support Fe3O4@MCM-41 and employed to catalyze styrene carbonate (SC) synthesis via the coupling reaction of styrene oxide (SO) with supercritical CO2 in the absence of organic solvent. The as-prepared catalyst was characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms and X-ray photoelectron spectroscopy (XPS). The results show that most Cu(acac)2 dispersed into the framework while n-Bu4NBr mainly on the surface of support. Cu(acac)2/n-Bu4NBr/Fe3O4@MCM-41 displayed higher catalytic activity than that of homogenous catalytic system composed of Cu(acac)2 and n-Bu4NBr, and 87.5% SC yield was obtained under optimized conditions. The recyclability of binary supported catalyst was also performed and no obvious loss in the activity was observed at the initial 3 cycles. The catalytic performance of the recovered catalyst can be enhanced by supplementing moderate amount of n-Bu4NBr after the third run. Keywords: Cu(acac)2; n-Bu4NBr; Carbon dioxide; Styrene epoxide; Styrene carbonate