Carbon nanotube production from greenhouse gases during syngas synthesis

Abstract

The impact of climate change around the world has led governments, institutions and \nindustries to increase their efforts to combat it by seeking new and innovative \ntechnologies. Carbon dioxide (CO2) is believed to be the primary reason for global \nwarming. Therefore, the capture and transformation of some of the billions of tons of \nCO2 produced annually by burning fossil fuels into useful products such as carbon \nnanotubes (CNTs) and carbon nanofibers (CNFs) is one of the methods being pursed in \ncurrent research activities. The conversion of two major greenhouse gases, CO2 and \nmethane (CH4), into CNTs and synthesis gas, which is a mixture of carbon monoxide \n(CO) and hydrogen (H2) has been studied experimentally by passing a CO2/CH4 mixture \nthrough a vertically orientated Chemical Vapour Deposition (CVD) reactor at \ntemperatures ranging from 650°C to 950°C . Two different catalysts were used, a \nlanthanum nickel alloy (LaNi5) and a mischmetal nickel alloy. Transmission electron \nmicroscopy (low and high magnification), Raman spectroscopy and gas chromatography \nwere used to analyze the products from the experiment. The apparent activation energy \nfor CH4 and CO2 consumption, and H2 and CO production were estimated to be 41.7, \n47.5, 54.5 and 47.5 kJ/ mol, respectively in the temperature range 1023 – 1123K. The \nCO2 and CH4 were decomposed, forming CNFs and CNTs as shown by the transmission \nelectron microscope images. The findings showed that as the temperature increased the \nCNFs and CNTs became, less defined and fewer in number. The mischmetal nickel alloy \nhad a smaller amount of amorphous carbon deposit compared to the lanthanum nickel \nalloy.