Encapsulation of cobalt complexes in zeolite Y for use as hydroformylation catalysts
In industry, the hydroformylation reaction is predominantly homogeneously catalysed using carbonyl complexes of cobalt and rhodium (1-3,45). The main disadvantage of homogeneous catalysts is that, especially for the longer chain hydrocarbon systems, very energy-intensive methods (such as distillation) are required to remove them from the reaction products. These separation techniques usually lead to losses of the catalyst. From an economic viewpoint, this is highly undesirable since the catalysts (especially rhodium) are expensive. Research has been carried out on encapsulating the catalysts within the cages of a zeolite, maintaining the activity of the catalyst while allowing it to be easily removed from the reaction medium ( eg. by filtration). However, all research reported so far has only considered rhodium catalysts (1,66-71,87). Furthermore, in most cases, leaching of the rhodium from the zeolite was significant enough to be undesirable. No successful research has been reported on encapsulating cobalt in zeolites for use as a hydroformylation catalyst. In this study, the synthesis of cobalt complexes encapsulated in the supercages of zeolite Y was attempted. The species initially present on the zeolites were analysed by Fourier-Transform Infrared Spectroscopy (FT-IR) and identified by comparison with the IR spectra of pure cobalt complexes synthesised independently in the laboratory. The impregnated catalysts were washed with various solvents to see if the cobalt complex remained in the zeolite. The impregnated zeolites were also tested as hydroformylation catalysts and compared with homogeneous catalysts.
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