Chem
Volume 9, Issue 3, 9 March 2023, Pages 739-754
Journal home page for Chem

Article
Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

https://doi.org/10.1016/j.chempr.2023.02.002Get rights and content
Under a Creative Commons license
open access

Highlights

  • A high uptake of benzene up to 3.92 mmol/g at 1.2 mbar and 298 K

  • A high selectivity of 166 for an equal volume benzene/cyclohexane (v/v = 1/1) mixture

  • Analysis of binding mechanism of benzene and cyclohexane within the porous materials

  • Direct visualization of reversible binding of benzene at an open Cu(II) site

The bigger picture

Benzene is an important volatile organic compound (VOC) with high prevalence and toxicity, which poses a serious threat to human health. The separation of benzene and cyclohexane is vital for the production of high-purity cyclohexane in petrochemical industries. Conventional adsorbents such as activated carbons and zeolites often suffer from structural disorder, restricting the visualization of binding sites and host-guest interactions. Herein, we report a comprehensive study of adsorption of benzene and cyclohexane in a series of ultra-stable metal-organic framework materials. We demonstrate that the precise control of pore size and pore chemistry provides a powerful strategy to enhance adsorption affinity and selectivity of benzene vs cyclohexane, even in the presence of water. We found that single-atom sites anchored within the pores promote high adsorption of benzene at low pressure.

Summary

Benzene is an important air pollutant and a key chemical feedstock for the synthesis of cyclohexane. Because of the small difference of 0.6°C in their boiling points, the separation of benzene and cyclohexane is extremely challenging. Here, we report the high adsorption of benzene at low pressure and efficient separation of benzene/cyclohexane, achieved by the control of pore chemistry of two families of robust metal-organic frameworks, UiO-66 and MFM-300. At 298 K, UiO-66-CuII shows an exceptional adsorption of benzene of 3.92 mmol g−1 at 1.2 mbar and MFM-300(Sc) exhibits a high selectivity of 166 for the separation of benzene/cyclohexane (v/v = 1/1) mixture. In situ synchrotron X-ray diffraction and neutron powder diffraction, and multiple spectroscopic techniques reveal the binding mechanisms of benzene and cyclohexane in these materials. We also report the first example of direct visualization of reversible binding of benzene at an open Cu(II) site within metal-organic frameworks.

Keywords

benzene
cyclohexane
metal organic framework
single-atom site
benzene separation and capture
structure
mechanism of binding
copper
scandium

UN Sustainable Development Goals

SDG7: Affordable and clean energy
SDG9: Industry innovation and infrastructure
SDG12: Responsible consumption and production

Data and code availability

The crystallographic data of the MOFs reported in this work have been deposited in the Cambridge Crystallographic Data Centre (CCDC) under accession numbers CCDC: 2172637 (benzene@MFM-300(Sc)), 2172638 (cyclohexane@MFM-300(Sc)), 2172639 (benzene@MFM-300(V)), 2172640 (cyclohexane@MFM-300(V)), 2172643 (benzene@MFM-300(Cr)), 2172632 (cyclohexane@MFM-300(Cr)), 2172642 (benzene@MFM-300(Fe)), 2172645 (cyclohexane@MFM-300(Fe)), 2172641 (benzene@MFM-300(Al)), 2172635 (cyclohexane@MFM-300(Al)), 2172633 (benzene@MFM-300(Ga)), 2172634 (cyclohexane@MFM-300(Ga)), 2172644 (benzene@MFM-300(In)), 2172636 (cyclohexane@MFM-300(In)), 2172646 (benzene@UiO-66), 2172650 (cyclohexane@UiO-66), 2172649 (benzene@UiO-66-defect), 2172653 (cyclohexane@UiO-66-defect), 2172648 (benzene@UiO-66-Cu), 2172652 (cyclohexane@UiO-66-Cu), 2172647 (benzene@UiO-66-Cu), 2172651 (cyclohexane@UiO-66-Cu), and 2184189 (d6-benzene@ MFM-300(Sc)). This paper does not report original code. Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

Cited by (0)

8

Lead contact