Methane decomposition to tip and base grown carbon nanotubes and CO_x-free H₂ over mono- and bimetallic 3d transition metal catalysts

Abstract

Catalytic shale gas decomposition for tunable tip/base grown CNTs and CO2-free H2.

Methane decomposition into CO x ‐free hydrogen over a Ni‐based catalyst: An overview

“…Owing to the pressure build‐up caused by the formation of graphite layers in the interior, metal particles are detached from the support (tip growth). Carbon filaments continue to grow as long as the metal is exposed to methane until excess carbon covers the metal particle surface 83 . On the contrary, if the interaction is very strong, then, carbon nanomaterials grow with Ni particles and remain attached to the support as diffused carbon cannot lift the metal particles from the support surface (base growth).…”

“…To prolong the catalyst lifetime, carbon deposited on the catalyst should be removed by combustion or gasification. The degree of difficulty of carbon removal depends on the type of carbon growth on the support, where the removal of carbon by base growth is considered to be easier 83 …”

Methane Pyrolysis for CO2‐Free H2 Production: A Green Process to Overcome Renewable Energies Unsteadiness

“…Transition metals like Ni, Fe, and Co have been widely studied as active species for methane pyrolysis [20,29,[57][58][59][60][61] due to their high activity, moderate operating temperature, and the possibility of producing valuable carbon nanotubes as by-product [62]. Their 3d orbitals are partially filled and can accept electrons from the C-H bonds of methane, which facilitates its decomposition [20,29,[57][58][59][60][61]63]. These metals also offer high solubility and carbon diffusion through their crystalline structure [64].…”

“…These metals also offer high solubility and carbon diffusion through their crystalline structure [64]. The following trend with respect to their activity has been reported: Ni > Co > Fe [57,60,61,[65][66][67]. Nickel-containing catalysts have been extensively investigated since Ni is considered the most active metal for this process [68,69].…”

“…Nickel-containing catalysts have been extensively investigated since Ni is considered the most active metal for this process [68,69]. However, nickel-based catalysts deactivate rapidly at temperatures above 600°C because the active metal sites are encapsulated within the carbon formed during the reaction [20,27,57,60,66,[70][71][72][73][74]. In the case of cobalt catalysts, their activity is lower compared to nickel catalysts [75,76].…”