Cu2Ox2+-ZSM-5 structure and its catalytic mechanism for oxidation of methane to methanol

Copper⁃based zeolite catalyst has the catalytic ability for the direct oxidation of methane to methanol under low⁃temperature conditions. Based on the structure and stability differences of Cu2O22+ -ZSM-5 formed by the pre⁃ treatment of O2 on Cu2 2+ -ZSM-5，the successive processes of Cu2 O2 2+ -ZSM-5→Cu2 O2+ -ZSM-5→ Cu2 2+ -ZSM-5 to catalyze the direct oxidation of methane to methanol were investigated by employing density func⁃ tional theory. The purpose is to obtain the structure of Cu2Ox2+-ZSM-5 (x=1，2) catalysts and the catalytic per⁃ formances for the direct oxidation of methane to methanol. The results show that the Cu2 2+ - ZSM - 5 prefers to form three kinds of Cu2O22+-ZSM-5 configurations involving O—O bond that the (CuO)22+ -ZSM-5，CuOOCu2+ - ZSM-5 and CuO2Cu2+ -ZSM-5 while the break of O—O bond leads to CuOCuO2+ -ZSM-5 configuration with poor stability requiring high temperature and formation energy barrier. All of (CuO)22+ -ZSM-5，CuOOCu2+ -ZSM-5 and CuO2Cu2+ -ZSM-5 as well as Cu2O2+ -ZSM-5 can catalyze the direct oxidation of methane to meth⁃ anol. The CuO2Cu2+ -ZSM-5 presents the highest catalytic performances where the determining⁃step is the dissocia⁃ tion of adsorbed CH4 with the energy barrier of the determining⁃step of 150.69 kJl/mol and the total reaction energy of -131.60 kJ/mol. The analysis of electronic structure indicates the correlation of high catalytic performance with a high level of electron delocalization and close p⁃band center relative to the Fermi level.