Ni–Cu–Zn/MCM-22 catalysts for simultaneous production of hydrogen and multiwall carbon nanotubes via thermo-catalytic decomposition of methane

Abstract

Pure hydrogen and carbon nanotubes were produced via thermo-catalytic decomposition (TCD) of methane over Ni-loaded MCM-22 catalysts in a vertical fixed-bed reactor. The effect of reaction temperature, gas hourly space velocity (GHSV), Cu/Zn promoter and time on stream on the methane conversion, hydrogen and carbon yields were studied over the synthesized catalysts. The catalytic performance of the 50%Ni–5%Cu–5%Zn/MCM-22 catalyst was found to be highly stable compared to other catalysts. The highest conversion of methane over 50%Ni–5%Cu–5%Zn/MCM-22 catalyst reached 85% with 947% carbon yield. Methane conversion increased on increasing the reaction temperature up to 750 °C and decreased thereafter at higher temperatures. XRD and TEM analysis of the carbon byproduct revealed that graphitic carbon appeared as a major crystalline phase during the reaction. HRTEM results revealed that most of the Ni particles were located on the tip of the carbon nanofibers/nanotubes formed on the spent catalysts. The carbon nanofibres have an average outer diameter of approximately 20–40 nm with an average length of 450–500 nm. Four types of carbon nanofibers were detected and their formation strongly depended on the reaction temperature, time on stream and degree of the interaction between the metallic Ni particle and support. The optimum conditions for CNT production within the experimental ranges were found at a reaction temperature of 750 °C.