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

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 Mnδ+ 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 Mnδ+ 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.