The framework of Li-2-SAPO-RHO showed some distortion under the ultra-high vacuum conditions in the transmission electron microscope (10 -5 Pa), likely due to dehydration (Fig. ). Similar distortions were observed in dehydrated Li-2-SAPO-RHO samples prior to singlecomponent adsorption measurements. Analysis of Li-SAPO-RHO samples with varying Li + content revealed that the elliptical 8MR apertures were comparable across samples, suggesting that aperture size does not account for the material's superior separation performance (Fig. and tables S11 to S16). Dynamical refinement of the cRED data revealed that most of Li + ions (denoted as Li1) occupy positions at the center of the 6-membered rings (6MRs) of Li-2-SAPO-RHO (fig. and tables S17 and S18). To further clarify the distribution of remaining Li + ions and Brønsted acid sites (H + ), neutron powder diffraction (NPD) experiments were conducted. A deuterated sample, 7 Li-2-SAPO-RHO, was prepared to reduce incoherent neutron scattering. High-quality NPD data were collected at 10 K using four detectors.