Mechanism of Si/Al ratio tuning in Cu-ZSM-5-catalyzed highly efficient methane-to-methanol conversion
SHEN Yuxin
YANG Chen
YU Chuan
YAN Ying
PU Yunhan
FU Mingli
Abstract：The Si/Al ratio of Cu-ZSM-5 zeolites is systematically investigated to regulate the catalyst structure and performance in the selective oxidation of methane to methanol under mild conditions.A series of Cu-ZSM-5-X(CZX)catalysts with varying Si/Al ratios are prepared via wet impregnation.Their physicochemical properties are characterized in detail using techniques such as X-Ray Diffraction(XRD),N2 physisorption,X-Ray Photoelectron Spectroscopy(XPS),and Electron Paramagnetic Resonance(EPR).Results reveal that the Si/Al ratio governs the distribution of copper valence states.Among the series,CZ50(measured Si/Al=44.58)possesses the highest proportion of active Cu+sites,with copper being highly dispersed on the zeolite support.Under reaction conditions of 70℃,3 MPa CH4,and 0.5 M H2O2 as the oxidant,CZ50 exhibits optimal catalytic performance,achieving a methanol productivity of 46.46 mmol·gcat-1·h-1 with 86.22％selectivity.This performance significantly surpasses that of catalysts with other Si/Al ratios.Mechanistic studies indicate that Cu+sites efficiently activate H2O2 to generate·OH radicals,which subsequently attack methane to form the key·CH3 intermediate.In situ IR spectroscopy combined with radical-quenching experiments confirms that the distinct electronic structure of CZ50 effectively stabilizes this methyl intermediate,thereby inhibiting deep oxidation to CO2.Through precise tuning of the zeolite Si/Al ratio,the valence state of copper active centers is modulated to favor the formation of highly efficient and stable Cu+sites.This strategy achieves highly productive and selective conversion of methane to methanol under mild conditions.The optimized CZ50 catalyst demonstrates methanol yields that exceed most reported systems,representing a key advance toward the practical realization of direct methane conversion and providing a novel design principle and a solid theoretical foundation for developing efficient,stable non-precious-metal catalysts for methane valorization.
Keywords：selective oxidation of methanemethanolCu-ZSM-5 catalystSi/Al ratioradical mechanismmild conditions
Publication Date：2026-01-31
Online Publishing Date：2026-03-20(First online date of this platform, not the publication date of the document)
Pages：12( 421-432 )