Single-Step Oxidation of Methane to Methanol over Superhydrophobic Modified NiO-Ce/Al₂O₃ Catalyst

Due to its acidity and high ionization energy and the strength of the C-H bond (439 kJmol^-1), there are challenges with the chemical utilization of CH₄. The low volumetric energy density of methane makes its transportation and storage difficult; this results in the flaring of methane. Instead of flaring, methane can be converted to a valuable product such as methanol, which is not only useful for transportation but can also be used as a valuable feedstock for other chemical syntheses.

In this study, we developed a gas phase reaction that involves passing CH₄, O₂ and H₂O over a superhydrophobic modified NiO-Ce/Al₂O₃ catalyst to selectively produce methanol. The catalyst was prepared by means of co-impregnation of nickel and cerium metal salts on Al₂O₃, followed by calcination at 450^oC and superhydrophobic modification with perfluoro alkyl. Different reaction conditions such as hydrophobic modification, steam flow rate, time on stream and methane-to-oxygen ratio were explored to determine the optimum conditions for higher productivity. The modified catalyst has a methanol productivity of 298 µmol.g^-1_Ni.h^-1, while the hydrophilic unmodified NiO-Ce/Al₂O₃ has a lower productivity of 35 µmol.g^-1_Ni.h^-1 after a 10 hr run in a tubular fixed-bed reactor. Increasing the reaction temperature and lowering the gas flow rate while increasing the CH₄:O₂ ratio enhanced the productivity of CH₃OH.

NiO-Ce/Al₂O₃ shows good activity towards direct methane-to-methanol conversion. It is evident that hydrophobic modification improves the activity and stability of this catalyst.