Isostructural rare-earth metal-organic frameworks for enhanced MTO product separation and efficient methane storage

Abstract

The development of crystalline porous materials with efficient gas separation and storage capabilities is crucial for reducing energy consumption and achieving carbon neutrality, yet it remains a formidable challenge. Leveraging the advantages of cage-like structures in gas separation and storage, and based on our previous research progress in rare-earth organic frameworks, two isostructural rare-earth MOF materials were synthesized, i.e., fcu-BPyDC-Yb and fcu-BPyDC-Y, respectively. Using rare-earth ions as the metal source and a dicarboxylate ligand of 2,2'-bipyridine as the connector, both materials were successfully fabricated via solvothermal synthesis. Their structures were characterized by means of single-crystal X-ray diffraction, and their performances were evaluated through nitrogen and light hydrocarbon sorption isotherms, MTO product mixed gas breakthrough experiments, and theoretical model calculations, as well as high-pressure methane storage measurements. These results indicate that fcu-BPyDC-Y, due to its slightly larger pore sizes (9.2 vs. 8.2 Å; 16.2 vs. 15.1Å), higher surface area (2501 vs. 2114 m² g-1), and pore volume (0.96 vs. 0.80 cm³ g-1) compared to fcu-BPyDC-Yb, demonstrates superior propylene adsorption capacity (209.5 cm³ g⁻¹), C3H6/C2H4 selectivity (9.1), and moderate propylene adsorption enthalpy (32.48 kJ mol⁻¹), along with relatively high volumetric methane storage working capacity (178 cm3 (STP) cm-3).