Photocatalytic oxidation of CH₄ to oxygenates on Fe(III)O_x/ZnO

A series of nFe(III)O_x/ZnO photocatalysts with different Fe contents was prepared by impregnation method, and the samples were characterized by XRD, N₂ physisorption, TEM, XPS, UV-vis and PL. It was found that by changing the concentration of Fe species in the impregnation solution, the Fe content in the final sample could be properly adjusted. Within the scope of this work, the loading of Fe does not cause significant changes in the phase, morphology, and porous structure of the ZnO support. However, the electronic state of the catalyst surface was altered considerably, with more O-vacancies were introduced. Fe species enhanced the separation of photo-induced electron-hole pairs, which was responsible to improve the performance of photocatalytic CH₄ conversion. Through the optimization of solvent volume, H₂O₂ concentration and reaction time, the 0.1Fe(III)O_x/ZnO sample showed the best performance over which the yield and selectivity of liquid oxidation products (CH₃OH, CH₃OOH, HCHO) was 5443 μmol/(g_cat·h) and 99%, respectively. Based on radical quenching experiments, it was found that the ·\rmO_2^- radicals derived from H₂O₂ played a major role for the activation of CH₄ to ·CH₃.