Hollow AMn2O4-δ (A = Co, Zn, Ni) nanotube for direct photo-oxidation of methane to C1 and C2 alcohols at atmospheric pressure and room temperature

Methane (CH4) conversion is brought into research hotspot in the field of environment, and direct photo-oxidation of methane into C1 and C2 alcohols under moderate conditions remains a huge challenge. Herein, we report a series of hollow AMn(2)O(4-delta) (A = Co, Zn, Ni) spinel nanotubes (HNTs) for the direct photo-oxidation of methane (DPOM) reaction. The results of catalytic performance demonstrated that the CH4 conversion and the yields of high value-added liquid products arrange in order of ZnMn2O4-delta HNTs > CoMn2O4-delta HNTs > NiMn2O4-delta HNTs. The ZnMn2O4-delta HNTs exhibited a superior CH4 conversion of 53.9 %, a liquid product yield of 241.7 mu mol g(-1)h(-1) (CH3OH 40.1 mu mol g(-1)h(-1), CH3CH2OH 200.9 mu mol g(-1)h(-1)) and a selectivity of 100 % under light irradiation at atmospheric pressure and room temperature conditions. Xray photoelectron spectroscopy (XPS) and low-temperature electron paramagnetic resonance (EPR) analysis showed that the substitution of Zn ion at the A-site of manganate spinel significantly improved surface chemisorbed oxygen (O-alpha) and oxygen vacancy activity, which were beneficial to the formation of center dot CH3. Multi-technology photocatalytic activity characterizations results showed that ZnMn2O4-delta HNTs possessed a narrower band gap and greatly favored the separation of photogenerated carriers. Moreover, the DPOM reaction mechanism involving the formation and dehydrogenation of alkyl and alkoxy intermediates was proposed over AMn(2)O(4-delta) (A = Zn, Co, Ni) HNTs, which was investigated through temperature-programmed desorption of CH4 (CH4-TPD), in situ EPR, in situ Fourier transform infrared spectroscopy (FT-IR) and density functional theoretical (DFT) calculations. It emphasized that CH3OH was formed via the combination of center dot CH3 and center dot OH. And it was more inclined to generate CH3CH2OH through the intermediates *CH2CH3/*CH3O. This study could broaden the avenue toward the application of manganese-based spinel in the direct photo-oxidation of methane into alcohols and offer a disparate perspective on the role of the substitution of metal ion at the A-site in enhancing the photocatalytic performance.