discovered that iron-peroxo sites in Fe2(O2)(dobdc) (dobdc: 2,5-dioxido-1,4benzenedicarboxylate) preferentially adsorbed ethane over ethylene. Breakthrough experiments found that polymer-grade ethylene could be produced from one adsorption cycle from a realistic 10/90 ethane/ethylene mixed feed, highlighting the benefits of paraffin-selective separation processes. Despite the range of examples of mechanisms to enable paraffin/olefin separations discovered thus far through trial and error, rational design is not yet possible and design rules for paraffin-selectivity are not well established.