Effect on selective adsorption of ethane and ethylene of the polyoxometalates impregnation in the metal-organic framework MIL-101

Impregnation of ionic nanostructured units in the pores of metal-organic frameworks (MOFs) is one approach to modify their host–guest interactions. Although, the effect of this approach is well investigated in catalysis, drug delivery, and bio imaging, still little is known about its impact on the selective adsorption properties of MOFs. Here we report the impregnation of two different polyoxometalate (POM) nanoclusters (PW11 and SiW11) into chromium terephthalate-based MOF, MIL-101(Cr), to investigate the post-impregnation changes in selective adsorption behavior, which are observed in terms of an important paraffin–olefin separation, using ethane and ethylene, at high pressure. The PW11 and SiW11 POMs bring π-accepting tendency and highly electronegative oxygen atoms on their surface to MIL-101 structure that selectively increases the affinity of material for ethylene, which is confirmed from isosteric heats of adsorption and selectivity calculation. Impregnated samples retain about 74–81 % of working adsorption capacity, after regeneration by decreasing the pressure. This study shows that anionic metal-oxide nanoclusters (POMs) may be used to change the selectivity of MOFs for olefin molecules.