Synthesis of MWCNTs and hydrogen from ethanol catalytic decomposition over a Ni/La 2O 3 catalyst produced by the reduction of LaNiO 3

Abstract

In the present paper we present a clean process that allows the simultaneous production of hydrogen and carbon nanotubes based on catalytic decomposition of ethanol, which is a renewable energy source. The catalyst consists of Ni nanoparticles highly dispersed on La 2O 3, obtained by the reduction of LaNiO 3. The effect of reaction conditions, such as reaction temperature and ethanol heating temperature, on the gaseous composition of the produced gas and the characteristics of the carbonaceous deposits was studied. An increase of the reaction temperature leads to an increase in H 2 production. The carbonaceous deposits were characterized by TGA, Raman spectroscopy TEM and HRTEM analysis. TEM micrographs show that the nanotubes were multi-walled with inner diameters ranging from 4 nm to 12 nm and outer diameters up to 75 nm. At low reaction temperatures the production of fibers is favored. The best graphitized carbon material was obtained when ethanol reacts at the surface of the catalyst instead of products issued from the thermal decomposition of ethanol (CH 4, CO, CO 2, C 2H 6 and C 2H 4). The yield of carbon nanotube (CNT) and H 2 were 3.5 g CNT (g cat h) −1 and 39 L H 2 ( g h ) − 1 respectively at 700 °C. The inner diameter of the CNTs does not depend on the experimental conditions used, whereas the outer diameter strongly depends on the reaction temperature (from 500 °C to 700 °C). From HRTEM images two types of carbon materials were shown: one with parallel graphene layers and one with fishbone structure. The intershell spacings d ˆ 0 0 2 were measured, the average value was equal to 0.344 nm for parallel tubes, while in curvature the d spacing is higher: 0.360 nm.