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In-situ generation of highly-reactive FeIV=O and its contribution during CH4 conversion to CH3OH

Hailong Tang,Yongqing Ma,Ganhong Zheng,Chuhong Zhu,Meiling Wang,Yilin Lu,Xiao Sun

Photocatalytic CH 4 conversion to CH 3 OH under mild conditions is undoubtedly an efficient strategy to realize CH 4 upgrading. In this work, in-situ formed highly reactive Fe IV =O complex with a bound Cl axial ligand was detected at ambient temperature and its contribution to CH 4 photoxidation to CH 3 OH was deeply investigated. Under optimized experimental condition, a high CH 3 OH yield of 3026.1 mmol mol Fe −1 (6.76 mmol g cat −1 h −1 ) with selectivity of 73.6 % was obtained during 8 h. Isotope labeling mass spectroscopy experiments manifested that O 2 was the only source of oxygen in products. The formation of Cl-(H 2 O) 4 Fe IV O complex was confirmed using low-temperature electron spin resonance spectroscopy and cryogenic Raman spectroscopy (ν(Fe O) = 828 cm −1 ). Through density functional theory (DFT) calculation, we showed that the Cl axial ligand acts as an “electron reservoir” during CH 4 conversion, i.e., electron acceptor during the process of CH 4 oxidation to CH 3 OH, while electron donor in CH 3 OH desorption. This not only lowered C-H cleavage energy, but also facilitated CH 3 OH desoption and inhibited overoxidation. As far as we know, Cl-(H 2 O) 4 Fe IV O is the first detected Fe IV O complex generated directly from O 2 and Fe 3+ at ambient temperature.