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.