The impact of Cu distribution in Cu/SAPO-34 catalyst on the continuous direct conversion of methane to methanol

Abstract

Direct oxidation of methane to methanol is a significant approach for utilizing natural gas and unconventional natural gas, reducing carbon emissions, and increasing energy efficiency. A series of Cu/SAPO-34 catalysts were successfully prepared using a simple and controllable solid ion exchange method for the continuous conversion of methane to methanol. The 1.5 wt% Cu/SAPO-34 achieves highest methanol yield of 178.3 μmol/(g_cat·h), while maintaining a methanol selectivity of 47 % at 400 °C. The distribution of copper in the zeolite significantly affects its direct conversion of methane to methanol. Through ex-situ DRIFTS, EPR, and H₂-TPR, all Cu/SAPO-34 catalysts contained two types of copper: one is isolated copper located on the hexagonal rings of the zeolite, which effectively conversion methane to methanol, and copper oxide nanoparticles in a cage, which easily cause over-oxidation of methanol. The in-situ DRIFTS confirmed the Cu²⁺-Cu⁺-Cu²⁺ redox cycle mechanism of the reaction.