Rational design of amino-functionalized pillar-layered Co6O6 cluster MOF for gas purification in the MTO process

The commercialization of the methanol-to-olefins (MTO) reaction has made significant progress in recent years. As the main products of the MTO reaction, the separation of C₃H₆ and C₂H₄ is of important significance for the chemical industry. This study introduces Amino-Functionalized Pillar-Layered Co₆-Cluster Metal-Organic Framework (PL-Co-MOF), an innovative ultra-microporous framework synthesized using 4-(4-carboxy-N-(4-carboxyphenyl)anilino)benzoic acid (NTA), 2-aminopyrazine (NH₂-Pyz), and cobalt salts under solvothermal conditions. The X-ray diffraction analysis was employed to confirm the detailed structure and phase purity of PL-Co-MOF. The calculated molecular electrostatic potential matches the interaction of the framework and MTO gas guest. The experimental data demonstrate that PL-Co-MOF exhibits a significantly higher adsorption of C₃H₆ in comparison to C₂H₄ at 298 K and 10 kPa. This evidence supports the exceptional selectivity of PL-Co-MOF towards a 50/50 C₃H₆/C₂H₄ ratio, which is 8.61. Breakthrough experiments confirm its effectiveness in separating C₂H₄ from C₃H₆/ C₂H₄ mixtures, with C₂H₄ elution time reached 46.6 min/g. Theoretical calculations reveal that the origin of excellent separation performance of a PL-Co-MOF is due to the oxygen sites in the Co₆O₆ clusters and the amino groups in NH₂-Pyz; In-situ FTIR of gases further verifies the absorption sites of the Co₆O₆ clusters and the amino groups in theoretical calculation results, which complementarily explains the real separation process of MTO gas molecules and frameworks. This highlights the importance of rational construction of MOFs for achieving efficient multicomponent separation. This work aims to advance adsorption separation technology and improve the gas purity of the MTO process.