Catalytic Potential of Carbon-Silica Composite Materials
Filip de Clippel1, *, Alexios Harkiolakis2, Stijn Van de Vyver1, Li Peng1, Gino Barron2, Pierre Jacobs1,
Joeri Denayer2, Bert Sels1
1
Centre for Surface Science and Catalysis, KUL, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium
2
Department of Chemical Engineering, VUB, Pleinlaan 2, 1050 Brussel, Belgium
*: presenting author, email: filip.declippel@biw.kuleuven.be
Introduction
Gaining structure in carbon materials always has been a challenge, but recently mesoporous
structured carbon could be developed by templating techniques. Meanwhile carbon molecular sieves,
obtained by carbonization of polymer precursor materials, have been investigated thoroughly.[1] Most
efforts however focus on the synthesis of pure carbon materials and research on microporosity is scarce.[2]
We present carbon silica materials (CSM) obtained by the synthesis of nano-sized graphitic crystallites
inside the mesopores of a silica template and their use in sorption and catalysis.
Experimental
CSMs were obtained by carefully filling the poresystem of MCM-41 with a furfurylalcohol
mesitylene carbon precursor solution by incipient wetness impregnation. By subsequent polymerisation
and pyrolysis intraporous nano graphitic crystals could be obtained. Activation of the CSM was achieved
by grafting, sulfonation and mild oxidation techniques.
Results and Discussion
The carbon deposition, and therefore the porosity of CSMs, could be controlled by changing the
pyrolysis conditions and the FA concentration in the precursor solution as evidenced by TGA and N2
sorption. As such a meso-, bi- or microporous pore sytem could be obtained. The microcrystalline
structure of the carbon was investigated by Raman and XRD and the resulting hypothesis of intraporous
graphitic nanocrystals could be visualized by HRTEM. A molecular probe study by pulse and breaktrough chromatography using lineair and branched paraffins demonstrated shape selective properties.[3]
Reagens selective catalysis was obtained in epoxidation of bulky and linear olefins. The selectivity
could be controlled by the amount of carbon as well as the pyrolysis conditions. Also the potential benefit
of an apolar backbone has been showed by an increased activity of CSM in esterification reactions
compared to classical aluminosilicates. The presence of two components, inherit to a composite material,
makes selective functionalisation possible. As such Sn grafted CSM materials have been developed in
which weak brønsted groups were introduced into the carbon component by mild oxidation in air. These
catalysts are highly active in the conversion of bio-mass derived dihydroxyaceton towards aded-value
alkyllactates. Secondly sulfonated CSMs were silylated with amine functional groups. These catalysts
combine incompatible acid and basic fiunctionalities. Their simultanous activity has been demonstrated
by enzyme mimicking in the conversion of benzaldehyde dimethyl acetal to beta-nitro-styrene.
Conclusions
A controlled synthesis of templated nano-graphitic crystals has been achieved. Shape selectivity, as
demonstrated in sorption experiments,[3] could be transferred towards catalytic applications in competitive
epoxidation. Activation techniques, selective to one of the composite’s components, make the production
of highly active bifunctional CSM based catalysts possible.[4]
References
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4)
H.C. Foley, Micropor. Mater. 4 (1995) 407-433.
T.G. Glover et al., Micropor. Mesopor. Mater. 111 (2008) 1-11.
F. de Clippel et al., Chem. Commun. 46 (2010) 928-931.
F. de Clippel et al., Green Chemistry (submitted).