Efficient Splitting of Alkane Isomers by a Bismuth‐Based Metal‐Organic Framework with Auxetic Reentrant Pore Structures

The isolation of di‐branched alkanes from their isomers is vital in gasoline upgrading to achieve high octane numbers but is significantly challenging and energy‐intensive. Here, we report the highly efficient separation of hexane isomers by combing molecular recognition and size‐sieving in a bismuth‐based MOF, UU‐200. The unique auxetic structure with reentrant honeycomb‐like pore cavities connected by narrow pore windows endows UU‐200 with a complete rejection of di‐branched alkanes and high capacities for linear and mono‐branched isomers. The molecular sieving effect, unprecedented separation selectivities, and excellent efficiencies are proved via adsorption isotherms and breakthrough experiments with high research octane numbers obtained (>96), indicating a benchmark for alkane separation under ambient conditions. The molecular recognition mechanism was unveiled by theoretical simulation and in situ Fourier‐transform infrared spectroscopy. Efficient gasoline upgrading with a research octane number (RON) higher than 96 was achieved in a reentrant auxetic honeycomb‐like bismuth‐based MOF with a combined fitting of pore window and chemistry. It enables the unprecedented exclusion of di‐branched isomers and molecular discrimination of linear and mono‐branched alkanes.