期刊
JOURNAL OF CATALYSIS
卷 234, 期 2, 页码 256-267出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2005.06.020
关键词
CO2 fixation; cycloaddition; propylene oxide; supercritical CO2; propylene carbonate; high pressure in situ EXAFS; deactivation; zinc pyridine-based catalyst
Homogeneous and heterogeneous zinc-based catalysts were tested in the reaction of propylene oxide and CO2 to propylene carbonate without the use of additional solvents. For the preparation of the heterogeneous catalysts, the homogeneous zinc pyridine bromide and acetate complexes were modified for chemical anchoring on a silica surface. All intermediate stages of the series, starting with the zinc pyridine-based complex and ending with the anchored complex, were catalytically tested and characterized. Rates in terms of turnover frequencies (TOFs) > 1100 h(-1) were obtained with the homogeneous zinc pyridine bromide-based catalysts, and TOFs of 330 h-1 were obtained with the corresponding heterogeneous catalyst. Using acetate instead of bromide as a ligand significantly decreased the performance. The differences in activity could be traced to structural differences unraveled by X-ray absorption spectroscopy (XAS). For the heterogeneous catalysts, special attention was paid to the deactivation behavior and the reusability. The catalyst structures were followed in situ by XAS using a specially designed batch reactor cell. This provided important information on the fate of zinc and bromide under reaction conditions and also gave new insight into the reaction mechanism. (c) 2005 Elsevier Inc. All rights reserved.
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