Simultaneous Production Of Multi-walled Carbon Nanotubes And Hydrogen By Ethanol Decomposition

In this work, a concept of the simultaneous production of multi-walled carbon nanotubes(MWCNTs) and hydrogen from ethanol decomposition has been elaborated. Ethanol decomposition was studied over Fe/Al₂O₃,CO/Al₂O₃ and Ni/Al₂O₃ catalysts which were prepared using a hydrothermal method. The effect of the catalyst component, metal loadings and reaction temperatures on the performance of hydrogen production and the quality of MWCNTs were systematically investigated by means of GC, BET, XRD, EDS, SEM-BEI, TEM. The growth mechanisms of MWCNTs over the different catalysts were proposed. The role of hydrogen in CVD synthesis of MWCNTs was emphatically studied. Based on the products of ethanol decomposition and the related thermodynamics analysis, a preliminary study on the reaction of ethanol decomposition was carried out.On the basis of the amount of hydrogen production and the quality of MWCNT growth, the results show that the five samples of Co(10 %(mol))/Al₂O₃, Co(20 %(mol))/Al₂O₃, Fe(40 %(mol))/Al₂O₃, Co(50 %(mol))/Al₂O₃ are the suitable catalysts for ethanol decomposition to produce hydrogen at an optimum temperature of 600℃in 50 min, and the total amount of hydrogen reached to 6894, 7545, 8226, 8545μmol, respectively.According to TEM images, the growth mechanisms of MWCNTs in ethanol decomposition over Co/Al₂O₃, Ni/Al₂O₃ and Fe/Al₂O₃ catalysts were following the base-growth mode, tip-growth mode and a mixture of tip-growth and base-growth mode, respectively. Some open-ended MWCNTs were obtained by ethanol decomposition, indicating that the certain amount of hydrogen participated in the reaction to form C-H bond that occurred on the nanotube ends.In addition to carbon deposition on the catalyst and a high yield of hydrogen formation in tail gas, a certain percent of CO and an insignificantly small percent of CH₄ and CO₂ were formed from ethanol decomposition. The amount of H₂ and CO increased with the temperature rising, and in contrast, CO₂ and CH₄ decreased with temperatures. Based on the above result, a preliminary investigation on the reaction of ethanol decomposition was proceeded and the possible reaction occurred during ethanol decomposition were suggested.