| Summary: | This study reports the synthesis of carbon materials (carbon nanotubes (CNTs), coiled carbon
nanofibers (CCNFs) and carbon spheres (CSs)) using the chemical vapour deposition (CVD)
method. The as-synthesized carbon materials were functionalized using nitric acid in order to
introduce functional groups and improve the hydrophilic behavior of the carbon materials. Both
the as-synthesized and functionalized carbon materials were characterized by TEM, TGA,
Raman and FTIR spectroscopy. The presence of functional groups was confirmed by alkalimetry
titration and IR spectroscopy data. Ceria (synthesized using the sol-gel method), activated carbon
(AC) and titania (P25) were other catalysts supports used and their morphologies were
determined by TEM.
Platinum was deposited on the various supports to give Pt loadings of 0.5, 1 and 5 % using the
polyol method. It was found that small Pt particle sizes were obtained with average particle sizes
of 1.8, 2.3, 2.6, 2.9, 2.7 and 1.6 nm for Pt/CCNF, Pt/CNT, Pt/CS, Pt/AC, Pt/CeO2 and Pt/TiO2
respectively at 0.5 % Pt loading. Pt was also deposited on the CeO2/CM supports (5 % and 10 %
CeO2 loadings) to make Pt-CeO2/CM catalysts. The Pt supported catalysts were characterized by
TEM, EDS, XRD, TPR, BET and TGA.
The platinum supported catalysts were tested for the hydrogenation of ethylene. The effect of
functionalization of the carbon materials was determined. Pt/functionalized carbon materials had
better activity than Pt/as-synthesized carbon materials. On the effects of supports; Pt/TiO2
showed the best activity compared to Pt/CCNF, Pt/CNT, Pt/CS, Pt/AC, Pt/CeO2 and this was
attributed to the small Pt sizes formed on TiO2 (Pt mean size was 1.6 nm). An interesting feature
in this study was the higher activity of the Pt-CeO2/CM as compared to Pt/CM. This was due to
the effect of ceria in preserving the surface area of Pt by suppressing sintering. The effect of
increasing the ratio of hydrogen to ethylene was investigated and the findings indicated that all
the ethylene was converted to ethane. This was attributed to the fact that at a high hydrogen
concentration, the rate of formation of the carbon deposit is slow and the rate of hydrogenation is
high. No carbon deposits are thus expected on the Pt catalyst particles. It was found that an
increase in the Pt loading resulted in an increase in the rate of reaction.
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