Surface Affinity Modification of High-Silica MFI Zeolites for Preferential Ethane Capture over Ethylene

Abstract

The highly efficient separation of C₂H₆/C₂H₄ meets great challenges due to their similar physicochemical properties and molecular dimension. Herein, pure silica MFI zeolite was incorporated with different heteroatoms (Mn, Cu, Ni, and Zn) to achieve appropriate surface polarity. The results showed that the Mn sites in the zeolite frameworks could enhance the affinity toward both C₂H₆ and C₂H₄. Additionally, the P modification over Mn-containing MFI zeolites was conducted to restrict the electron transfer effect of Mn^δ+ species. Notably, with the P content increased, the C₂H₄-favored separation behavior was surprisingly reversed to the C₂H₆-favored separation behavior. The isosteric adsorption heat and desorption active energy further confirmed the superior surface affinity of C₂H₆ to C₂H₄ on the Mn- and P-functionalized MFI zeolite. Finally, the X-ray photoelectron spectroscopy spectra, Raman spectra, and grand canonical Monte Carlo simulations further proved that the bonding between P and Mn could decrease the structural defects and weaken the electron transfer of Mn^δ+ species within the functionalized zeolite, which exhibited significant impacts on the preferential capture of C₂H₆ versus C₂H₄ molecules. As such, an optimal trade-off between the dynamic C₂H₆/C₂H₄ separation selectivity and C₂H₆ uptake was realized by the cooperative strategy of Mn incorporation and P (triphenylphosphine) modification.