Continuous methane selective oxidation to methanol over Cu-SAPO-34

• Exceptional performance of Cu-SAPO-34 catalyst developed. • Water as the main oxygen source in MtM pathway. • The essential Cu 2+ -Cu + -Cu 2+ redox cycle sustained by trace oxygen highlighted. • Cu-OH species on six-membered rings as active centers identified. • CH 3 O⁻ intermediates during methane activation revealed. A Cu-SAPO-34 catalyst synthesized via a one-pot method exhibits exceptional performance in the selective oxidation of methane to methanol. In this system, water serves as a key reactant, while trace oxygen acts as an oxidant to enhance catalytic activity by facilitating methane activation; Isotopic labeling experiments combined with temperature-programmed surface reaction analysis confirm that the oxygen in methanol originates predominantly from water, highlighting the critical role of water in the reaction pathway; In situ UV-Vis spectroscopy reveals the operation of a Cu²⁺-Cu⁺-Cu²⁺ redox cycle, which is indispensable for catalytic activity, with trace oxygen proving necessary to sustain the cycle. In situ FTIR spectroscopy identifies Cu-OH species located on the six-membered rings of Cu-SAPO-34 as potential initial active centers, with their consumption during methane activation accompanied by changes in Brønsted acid sites. NMR spectroscopy further demonstrates weak methane adsorption on the zeolite surface and the formation of CH₃O⁻ intermediates during the reaction. These findings provide a comprehensive mechanistic understanding of methane selective oxidation over Cu-SAPO-34, offering valuable insights for the development of efficient methane-to-methanol conversion technologies.