Preparation of Cu-Based Spherical Micromesoporous Material by Using Sepiolite Toward Methanol Production from Catalytic Oxidation of Low-Concentration Coalbed Methane

Direct catalytic oxidation (DCO) of coalbed methane to methanol has been considered as a significant technology for highly efficient and clean utilization of coal resources. Herein, the Cu-based spherical micromesoporous material (Cu/SMMM) was successfully prepared by using a sepiolite-derived silica source, and the DCO of methane to methanol was achieved under a low-temperature gas-phase system. Under the optimal reaction conditions, the Cu/SMMM accomplished the maximum methanol production of 69.3 μmol/g_cat/h and methanol selectivity of 81.2% with full activation at 450 °C in air for 4 h, and the reaction was carried out at 320 °C for 1 h. Various characterizations demonstrated that the unique SMMM promoted the dispersion of copper oxides to form more active copper species and Lewis acidic sites (LAS). The variable-temperature FTIR, XAS, and NO-IR analyses identified that the highly dispersed dimeric copper species such as ([Cu₂(μ-O)]²⁺ or [(Cu₂O₂)²⁺]) in Cu/SMMM was the major active species for DCO of methane into methanol. Additionally, combined with in situ FTIR analysis, the catalytic mechanism was revealed, in which the adsorbed methane species could be converted to CH₃* species. Subsequently, CH₃* species bound to oxygen of the dimeric copper species to form CH₃O* species, which was then converted to methanol in the presence of water.