Carbon nanotube production from greenhouse gases during syngas synthesis

Abstract

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