The catalytic hydrogenation of α,β-unsaturated carbonyl compounds can lead to several different products, of which the unsaturated alcohol (en-ol) is most difficult to obtain. In this regard, cobalt is known to have a positive influence on platinum catalysts. Little is known about such an effect on more cost-effective nickel catalysts. Nickel and cobalt (5 mass % each) were supported on graphite (GRA), multiwalled carbon nanotubes (MWCNT), and activated carbon (AC). The catalysts were characterized by N2-physisorption, X-ray diffraction (XRD), H2-chemisorption, and high-resolution transmission electron microscopy. XRD indicated the formation of a Ni–Co alloy. For cinnamaldehyde as the substrate, the en-ol selectivity and the turnover frequency (TOF) of the catalysts increased in the order GRA < AC < MWCNT. Ni–Co/MWCNT showed the highest selectivity over the whole conversion range, and at a conversion of 63% (TOF: 14.4 h–1) the product contained 62% en-ol and 38% saturated aldehyde. A positive influence of both cobalt and the support (MWCNT) on the selectivity of nickel catalysts is clearly indicated.

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Single-walled carbon nanotubes were synthesized from graphite using the arc discharge technique. A nickel/yttrium/graphite mixture was used as the catalyst. After purification by sonication in a Triton X-100 solution, nickel-cobalt metal nanoparticles were deposited on the surface of the single-walled carbon nanotubes. The resulting material and/or the nanotubes themselves were characterized by physisorption, Raman spectroscopy, high-resolution transition electron microscopy and X-ray diffraction. Raman spectroscopy indicates that the nanotubes, prepared by the arc discharge technique, are semi-conducting with a diameter centering at 1.4 nm. The average nickel-cobalt particle size is estimated to be in the region of 8 nm. The catalytic activity of the material was examined for the hydrogenation of unsaturated fatty acid methyl esters obtained from avocado oil. The carbon nanotube supported nickel-cobalt particles effectively hydrogenate polyunsaturated methyl linoleate to monounsaturated methyl oleate. In contrast to a conventional nickel on kieselghur catalyst, further hydrogenation of methyl oleate to undesired methyl stearate was not observed.

A comparison of three different purification procedures for multi-walled carbon nanotubes (MWCNTs) produced by chemical vapour deposition (CVD) has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCl. Sample purity was documented with the Raman spectroscopy, Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and thermo gravimetric analysis (TGA). The Raman spectroscopy, SEM and TEM results showed that the liquid phase oxidation-acid refluxing route successfully eliminated most of the impurities without damaging the nanotube structure. TGA analysis showed in increase in density of MWCNTs with better oxidation resistance after purification and the metal content was reduced from 23.8 wt% to 5.4 wt%.

Multi-walled carbon nanotubes were synthesized by dc-arc discharge in helium atmosphere and the effect of calcination at different temperatures ranging from 300-600 degrees C was studied in detail. The degree of degradation to the structural integrity of the multi-walled carbon nanotubes during the thermal process was studied by Raman spectroscopy, Scanning electron microscopy and High resolution transmission electron microscopy. The thermal behaviour of the as prepared and calcined samples was investigated by thermogravimetric analysis. Calcination in air at 400 degrees C for 2 hours was found to be an efficient and simple method to eliminate carbonaceous impurities from the nanotube bundles with minimal damage to the tube walls and length. The impurities were oxidized at a faster rate when compared to the nanotubes and gave good yield of about 50%. The nanotubes were observed to be damaged at temperature higher than 450 degrees C. The results show that this method is less destructive when compared liquid phase oxidation with 5 M HNO3.