Electronic Material Properties - und Geowissenschaften ...

Diffusion and reaction in micro- and mesopores
Christoph Schüth
Diffusion in micro- and mesopores is in many cases limiting for mass transfer and
reaction rates in porous natural or synthetic materials. Accessibility and reactivity of
micro- and meso-pore domains should be a function of the pore sizes as well as pore
polarities. In natural po-rous media both parameters can be assumed to show a
distribution, depending on the type of the porous material. Moreover, educts and
products of a reaction may show different po-larities resulting in a distribution of
diffusivities with an impact on overall reaction rates.
The objective of this work is the synthesis and characterization of well-defined porous
mate-rials with different pore sizes and polarities containing catalytically active sites,
and study their accessibility with various methods. The catalytic hydrodehalogenation of
chlorinated hydrocarbons (trichloroethylene (TCE) and chlorobenzene) and the
hydrogenation of ben-zene serve as model reactions resulting in different product
distributions in terms of polarity and molecular size. The use of well-characterized
model solids should allow to relate diffu-sion rates and reactivities of the different
materials to pore sizes and pore polarities.
In the first step, the synthesis and first characterization of metal complexes will be
performed. The selection of the metal complexes is predefined by the model reactions
as described earlier. Pincer complexes (M-1a-c,2a-c) which are accessible by various
procedures will be synthesized. In general a number of organic and organometallic
transformations have to be performed to generate complexes M-1a-c,2a-c. Their special
features are the different donor atoms which coordinate to the metal, the functional
groups at the donor atoms and very important for this project the hydrolysable group at
the end of the spacer. These features allow to adjust the metal complexes for a special
application in catalysis.
(R'O) 3Si
X
[M]
X
M-1a-c, M-2a-c
Scheme 1
X = SR (1), NR 2 (2)
R = Me (a), Ph (b), Cy (c)
[M] = Rh, Pd, Ni, Ru complex fragments
R' = Me, Et
Spacer e.g. C 6-alkane or short PEG chain
It is planned to perform the dehalogenation reactions with the SCS-Pd complexes (Pd-
1). Catalysts of this type are highly stable in air and water and are known to cleave
carbon-chlorine bonds. This will be important for field applications planned at a later
date of this project. To fine tune the active center with respect to electron density and
steric hindrance R will be varied from methyl (Pd-1a), phenyl (Pd-1b) to cyclo-hexyl (Pd-
1a). All complexes will be screened for their catalytic activity in dehalogenation and
hydrogenation reactions.
- 144 -