Differential guest location by host dynamics enhances propylene/propane separation in a metal-organic framework.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 33257662.
- Also identified by DOI 10.1038/s41467-020-19207-9 and PMC identifier 7704659.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Energy-efficient approaches to propylene/propane separation such as molecular sieving are of considerable importance for the petrochemical industry. The metal organic framework NbOFFIVE-1-Ni adsorbs propylene but not propane at room temperature and atmospheric pressure, whereas the isostructural SIFSIX-3-Ni does not exclude propane under the same conditions. The static dimensions of the pore openings of both materials are too small to admit either guest, signalling the importance of host dynamics for guest entrance to and transport through the channels. We use ab initio calculations together with crystallographic and adsorption data to show that the dynamics of the two framework-forming units, polyatomic anions and pyrazines, govern both diffusion and separation. The guest diffusion occurs by opening of the flexible window formed by four pyrazines. In NbOFFIVE-1-Ni, (NbOF<sub>5</sub>)<sup>2-</sup> anion reorientation locates propane away from the window, which enhances propylene/propane separation.