MFI Zeolite Membrane with Surface Mo─O Clusters for Inverse CH₄/CO₂ Separation

Separation of methane (CH₄) and carbon dioxide (CO₂) is of significant industrial interest for the utilization of biogas, landfill gas and natural gas. While the state-of-the-art membranes are CO₂-selective, CH₄-selective membranes remain elusive, with potential applications in the recovery and purification of methane-rich gases such as biogas and landfill gas. Herein, we report a molybdenum-oxygen (Mo─O) functionalized MFI-type zeolite membrane for inverse CH₄/CO₂ gas separation. A pure-silica MFI-type zeolite membrane is first seeded grown on an alumina support and subsequently functionalized via facile impregnation and calcination of sodium molybdate. The as-prepared membrane features uniform pores (0.5 nm) and ultrasmall Mo─O clusters (1.6 nm). The Mo─O/MFI membrane selectively permeates CH₄ over CO₂, achieving an unprecedented CH₄/CO₂ separation factor of 11.8 alongside a high CH₄ permeance of 2.1 × 10^-8 mol s^-1 m^-2 Pa^-1. Experimental measurements and theoretical calculations reveal that CH₄ preferentially adsorbs onto Mo─O clusters via hydrogen bond and diffuses rapidly through MFI zeolite pores. This study represents the first demonstration of porous membranes enabling inverse CH₄/CO₂ separation and offers guidance for the design of next-generation CH₄-selective membranes.