II International Symposium on Carbon for Catalysis ABSTRACTS

PP-<strong>II</strong>-19
(NaOH, CsOH and NaN 3 ) loaded samples were also prepared by impregnation for
comparison.
The nitrogen adsorption isotherms were collected using the gas volumetric method in a
conventional all-glass BET apparatus for determining the pore size distribution. The mass
transport dynamics of propane was investigated by the batch type frequency-response
apparatus.
The Pt/carbon catalysts formed in situ after reduction were applied as heterogeneous
catalyst in flow-through microreactor to transform cyclohexane between 200 and 420 o C.
Results and Discussion
The changes in the nitrogen adsorption capacities and in the pore-size distribution of
small micropores with diameters 0.64 and 0.92 nm reflected the significant influence of the
loadings and treatments. The nitrogen adsorption data were used to determine the
microporosity of the sample with the two-term Dubinin-Radushkevich equation. The pore
sizes correspond to the thickness of two and three graphite layers, respectively. The
distributions of the parallel propane mass transport processes have been also recorded in
unloaded and loaded bimodal micropore systems of an activated carbon sorbent after various
treatments and modifications. The bimodal size distribution of the micropores and the
bimodal character of the FR spectra of intraparticle diffusion suggest that the smaller and the
larger micropores of the activated carbon are not interconnected. The macro and mesoporous
texture reflects the original texture of the precursor, the carbon source material. The SEM
examination suggested that the sorbent was prepared from a coal precursor. Very little
porosity existed between the extremely wide macro- and the very narrow micro-pores. Large
pores or channels contribute little to the total gas adsorption capacity at low relative pressures
but act as important transport pores with low diffusional resistance.
In activated carbons the microporosity responsible for the high surface area may act as
physical barrier to the metal particles deposited resulting in the resistance to sintering. This is
attributed to deposition of metal particles of high dispersion in narrow pores of the supports,
which renders part of the metal surface inaccessible to the organic substrates. Such a blocking
effect proved especially significant for Pt catalysts on the activated carbons with the smallest
micropores. The possibility of the loss a great part of the catalytically active surface due to the
blocking has long been recognised, however, there are not much examples of experimental
verification of such a phenomenon. Present results give significant examples.
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