Carbon nanotubes as advanced catalysts and catalytic supports for the liquid-phase aerobic oxidation of hydrocarbons: A review

The liquid-phase aerobic oxidation of hydrocarbons to more valuable oxygenized compounds is among the most crucial industrial processes. Traditionally, these processes were executed by using a stoichiometric amount of various toxic oxidants with homogeneous catalysts of transition-metal salts and complexes, which results in the production of a gigantic amount of corrosive and noxious waste. Recently, carbon nanotubes have gained momentous importance as catalysts and catalytic support in various chemical processes because of their unprecedented properties. Few researchers have actually employed carbon nanotubes and functionalized carbon nanotubes as catalysts and catalytic support for the liquid-phase aerobic oxidation of hydrocarbons. This review specifically focused on the use of carbon nanotubes and functionalized carbon nanotubes as catalysts and catalytic supports in the liquid-phase aerobic oxidation of hydrocarbons. A plausible mechanism of the reaction has also been drawn while thoroughly reviewing the previously reported data. The impact of impurities in carbon nanotubes on their catalytic activity for the liquid-phase aerobic oxidation of hydrocarbons has also been discussed. It is observed from the literature that oxygenated carbon nanotubes have a negative effect on their catalytic activity for the liquid-phase aerobic oxidation of hydrocarbons, while nitrogen doping and/or metal nanoparticle immobilization, the surface electron transfer between the modified carbon nanotubes and radicals enhanced and improved the catalytic activity. Furthermore, the nitrogen-doped and/or metal-nanoparticle-incorporated carbon nanotubes accelerate the decomposition of hydroperoxides, which are key intermediates in the liquid-phase aerobic oxidation of hydrocarbons, thereby improving the overall catalytic activity.