Contents - Akademi Sains Malaysia

ASM Science Journal, Volume 7(1), 2013performance of the hybrid catalysts for the synthesis ofCNTs were carried out using a fixed-bed chemical vapourdeposition reactor. The physical and chemical propertiesof the hybrid catalysts were then characterized usingX-ray diffraction (XRD), field emission scanning electronmicroscope (FESEM) and thermogravimetric analyser(TGA).MATERIALS AND METHODSPreparation of the CatalystsSeries of hybrid catalysts of Ni:Cu, Ni:Cr and Ni:Mndoped with Pr with the atomic ratio of 3:1:0.3 wereprepared from a mixture of nickel (II) nitrate hexahydrateNi(NO 3 ) 2 .6H 2 O, copper nitrate [Cu(NO 3 ) 2 ], manganese(II) acetate [(CH 3 COO) 2 Mn.4H 2 O], chromium (III)nitrate (Cr(NO 3 ) 3 .6H 2 O) and praseodymium (III) nitrate[Pr(NO 3 ) 3 .6H 2 O], respectively. Optimum quantities of therespected metal salts were dispersed in a sufficient amountof water and mixed well to get a homogeneous mixture ofthe salt solution. The mixture was dried at 80ºC for 24 hand calcined at 700ºC for 5 h. The catalyst mixture wasthen cooled and finely ground into fine powder of hybridcatalyst.Synthesis of Carbon NanotubesThe synthesis was carried out using a horizontal fixedbedCCVD reactor in atmospheric pressure. The reactorconsisted of a tube furnace with a quartz tube where thedecomposition of the acetylene gas took place (Figure1). About of 200 mg of catalyst was placed at the centre(hot zone) of the tube furnace. Nitrogen as the carriergas was simultaneously introduced into the reactor tubeat the flow rate of 0.3 l/min. The mixed gases were thenflown over the catalyst to allow the decomposition of thecarbon precursors to occur. The reaction was left for 30min at 700ºC. The reaction chamber was then cooled toroom temperature. The yield in the form of black powderwas collected and the percent of carbon composition wasdetermined from Equation 1:Carbon yield (%) = M 1M 2Where, M 1 is the mass of carbon deposited after the reactionand M 2 is the mass of catalyst used.The Hybrid CatalystsCHARACTERIZATIONThe identification of metallic bulk crystallographic andamorphous phase in the hybrid catalysts were carried(1)out by XRD. The analysis of the hybrid catalyst by XRDwere conducted using Diffractometer D500 SiemensCrystalloflex with CuKα (λ = 1.54060 Ǻ) as the radiationsource.The As-synthesized CNTsThe as-synthesized CNTs were characterized by theJSM-6701F field emission scanning electron microscope(FESEM) to determine the morphology of the CNTs. Thethermal stability and purity of the CNT was analysed usingthe Mettler Toledo TGA.X-ray DiffractionRESULTS AND DISCUSSIONThe type of metal oxide in the hybrid catalysts formulationis one of the factors that influence the catalytic activityand morphology of the deposited carbon (Chai et al.2007; Nyamori et al. 2008). XRD patterns of the hybridcatalysts were shown in Figure 2. From the diffratogrampattern, it shows that the active oxide phase, NiO present inNi:Cr/Nd and Ni:Mn/Nd catalysts. While in Ni:Cu/Ndcatalysts, Ni species tends to form the binary oxides ofNi 19 CuO 20 with high peaks intensity. It was identified inthis work that the presence of NiO phase had contributedto the high production of CNTs with the mass of yield 18times greater than the initial mass of the Ni:Cr/Nd andNi:Mn/Nd catalysts used respectively, but not for Ni:Cu/Nd catalyst.In comparison to the respective diffractograms pattern ofthe hybrid catalysts, it was observed that Ni:Cr/Nd was inthe amorphous form, while the hybrid Ni:Mn/Nd and Ni:Cu/Nd catalysts represented the polycrystallite form. This newformulated hybrid catalysts of the respected Ni:Mn/Nd andNi:Cu/Nd had generated two types of crystallite structures.Firstly, the spinal oxide of NiMn 2 O 4 which was observedin the hybrid Ni:Mn/Nd catalyst formulation, constructedfrom NiO and Mn 2 O 3 phases and served as the active sitefor the excellent catalytic performance in the production ofCNTs. Secondly, the ternary oxide of Nd 4 (CuNi)O 8 whichwas present in the Ni:Cu/Nd catalyst and constructed frommetal ions of various oxidation states of Ni 2+ , Cu 2+ andNd 3+ in the perovskite type of oxide. The ternary oxidein the hybrid catalyst of Ni:Cu/Nd existed as Ni 19 CuO 20phase, instead of Ni 20 O 20 (or NiO phase). The molecularformula of the perovskite oxide showed that one mole ofthe Ni site in the NiO lattice cluster was probably replacedby one mole of Cu 2+ ion, and resulted in the reduction of thecatalytic performance of the NiO phase in the formulatedNi:Cu/Nd hybrid catalyst.From the catalytic measurement of the Ni based hybridcatalysts, results obtained revealed that the incorporation2