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application is the separation and recycling of catalyst, which are the complexes of costly metals. One
such approach is to immobilize the catalyst.
Immobilised Catalyst (Catalyst Membrane)
Simon et al (2003) proposed a possible approach to overcome the separation and recycling problem in
industry by immobilisation of the cationic catalysts on anionic supports in a membrane configuration.
With the membrane there is possibility to perform two consecutive steps in one reactor. To demonstrate
this principle the hydrogenation and hydrolysis steps of the L-DOPA synthesis will be performed in one
pot as depicted in Figure 3.
Figure 3. The asymmetric hydrogenation and hydrolysis steps of the L-DOPA synthesis carried out
in a concept reactor
The immobilisation by ionic interaction has the advantage that proven homogeneous systems can directly
be immobilised without difficult ligand modification. Well-known systems, like Rh-MeDuPHOS and Ru-
BINAP will be immobilised on functionalised TUD-1. TUD-1 is a well-defined mesoporous (siliceous)
oxide, with high surface areas, easily tuneable pore size distribution and three-dimensional connectivity.
It will be functionalized with Nafion or heteropoly acids (HPA). After immobilisation of the catalyst, the
materials will be tested on activity and selectivity on various substrates, mostly dehydroamino acids.
Special attention is being paid to reusability and the occurrence of leaching. In the final part of the project
the asymmetric hydrogenation with these catalysts will be combined with an enzyme-catalysed
deacylation leading to e.g. L-DOPA.
REFERENCES
Knowles, W.S. 1983. "Asymmetric Hydrogenation". Acc. Chem. Res. Vol. 16, pp. 106-112.
Nugent, W.A, RajanBabu, T.V. and Burk, M.J. 1993. "Beyond Nature's Chiral Pool: Enantioselective
Catalysis in Industry". Science, vol. 259, No. 5094 pp. 479-483.
Shriver, D.F. and Atkins, P.W. 1999. Inorganic Chemistry. UK: Oxford University Press.
Simon, C et al. 2003. Catalytic membranes for asymmetric hydrogenation. [on-line]. Available from:
www.bt.tudelft.nl/content/boc/pdf/BocprSimons.pdf
[Accessed 24 Feb. 2005]
