Facile loading of Cu(I) in MIL-100(Fe) through redox-active Fe(II) sites and remarkable propylene/propane separation performance

- A novel Cu(I) loading method was developed by utilizing the redox-active Fe(II) sites in MIL-100(Fe).
- Fe(II) sites in MIL-100(Fe) act as antioxidants that protect the resultant Cu(I) species.
- Cu(0.6)@MIL-100(Fe) is superior to benchmark adsorbents considering both C3H6 selectivity and working capacity.
- Cu(0.6)@MIL-100(Fe) exhibits good separation and easy regeneration performance under mixed-flow conditions.

A novel Cu(I) loading method, which includes the reduction of CuCl2 to CuCl without an external reducing agent and high-temperature calcination, was developed using the redox properties of coordinatively unsaturated Fe(II) sites in MIL-100(Fe). The successful loading of Cu(I) ions and their redox-couple reactions are supported by various methods such as TEM/EDS, XPS, PXRD, and ICP-AES techniques, as well as N2 adsorption isotherms at 77 K. Compared to Cu loaded into isostructural MIL-100(Al) devoid of redox active sites, Cu(I)-loaded MIL-100(Fe) exhibits higher C3H6/C3H8 selectivity and superior air stability. This indicates that the Fe(II) sites in MIL-100(Fe) act as antioxidants that protect the resultant Cu(I) species, as well as reducing agents for CuCl2. Remarkably, in the typical pressure-swing adsorption (PSA) range (1-5 bar), the Cu(I)-loaded MIL-100(Fe) exhibits a large C3H6 working capacity as well as very high C3H6/C3H8 selectivities that are superior to those of the benchmark adsorbents, zeolite-13X and HKUST-1. Moreover, this material is easily regenerated under mild conditions and exhibits good separation performance under dynamic mixed-flow conditions. This facile method for loading Cu(I) can be applied to other adsorbents containing redox-active sites.

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