Efficient direct conversion of methane into methanol on CuZn hetero-diatomic catalysts with certain coordination spheres: a DFT study

Abstract

The oxidation of methane to a high-value-added chemical, methanol, is a major challenge in catalysis, requiring high energy input to overcome the CH₃–H bond activation energy barrier. Based on density functional theory (DFT) calculations, methane oxidation to methanol is catalyzed by hetero-diatomic catalysts (CuZn-NG) with different coordination spheres (CSs). Valence band maximum (VBM), atomic charge and d-band center are selected as analysis methods for the pathway selection and activity of catalysis. The VBM plays a vital role in the catalytic pathway selection, CuZn-NG catalyzes the direct conversion of methane into methanol without side reactions. Alarmingly, the most important reaction step, CH₃–H bond activation, is a spontaneously exothermic reaction (releasing 0.06 eV) with CuZn-N_PAG as the catalyst, in contrast to most other endothermic reactions in the same activation. By analyzing the atomic charge of the Cu center and O atom, the special electronic phenomenon for this important step is summarized as the “bow-release effect”. The CS affects the electronic properties of the active center and further affects the methane oxidation activity. This work provides a useful guide to understand the catalytic selectivity and activity of hetero-diatomic catalysts.