Ethylene Pretreatment Enhances Ethylene Adsorption and Separation over Cu@SAPO-RHO Zeolite

Abstract

Efficient ethylene/ethane (C₂H₄/C₂H₆) separation using low-energy technologies is crucial for the chemical industry yet remains challenging due to the lack of industrially applicable adsorbents. Cu(I)-based adsorbents show significant potential; however, traditional synthesis methods often involve complex procedures or reduction steps. Herein, we report that Cu@SAPO-RHO zeolite, synthesized for the first time via a one-pot method with cyclam as the Cu(II) ligand, exhibits a remarkable C₂H₄/C₂H₆ selectivity of 22.6, a C₂H₄ uptake of 3.08 mmol g⁻¹, and a separation factor of 9.4 under ambient conditions by using a C₂H₄ pretreatment, placing it among the best-performing zeolitic materials. The C₂H₄ pretreatment enhances separation efficiency by partially reducing Cu(II) to Cu(I) and water resistance through the formation of carbon species during pretreatment. Structural analysis using Rietveld refinement reveals that Cu²⁺ ions occupy the corners of elliptical single 8-rings (s8r). X-ray absorption near-edge structure analysis confirms a reduction in the Cu oxidation state, while X-ray photoelectron spectroscopy corroborates the partial conversion of Cu(II) to Cu(I). Periodic density functional theory calculations further reveal that Cu(I) interacts more strongly with C₂H₄ than Cu(II). With its straightforward synthesis and enhanced performance through C₂H₄ pretreatment, Cu@SAPO-RHO zeolite presents a promising solution for industrial-scale C₂H₄/C₂H₆ separation.