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 450oC 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-1Ni.h-1, while the hydrophilic unmodified NiO-Ce/Al2O3 has a lower productivity of 35 µmol.g-1Ni.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.