TiO₂ nanofiber-supported copper nanoparticle catalysts for highly efficient methane conversion to C1 oxygenates under mild conditions

The selective oxidation of methane under mild conditions remains the “Holy Grail of Catalysis”. The key to activating methane and inhibiting over-oxidation of target oxygenates lies in designing active centers. Copper nanoparticles were loaded onto TiO₂ nanofibers using the photo-deposition method. The resulting catalysts were found to effectively convert methane into C1 oxygenated products under mild conditions. Compared with previously reported catalysts, it delivers a superior performance of up to 2510.7 mmol·g_Cu⁻¹·h⁻¹ productivity with a selectivity of around 100% at 80 °C for 5 min. Microstructure characterizations and density functional theory (DFT) calculations indicate that TiO₂ in the mixed phase of anatase and rutile significantly increases the Cu⁺/Cu⁰ ratio of the supported Cu species, and this ratio is linearly related to the formation rate of oxygen-containing species. The Cu_I site promotes the generation of active O species from H₂O₂ dissociation on Cu₂O (111). These active O species reduce the energy barrier for breaking the C–H bond of CH₄, thus boosting the catalytic activity. The methane conversion mechanism was proposed as a methyl radical pathway to form CH₃OH and CH₃OOH, and then the generated CH₃OH is further oxidized to HOCH₂OOH.