In this study, we developed a SAPO-RHO zeolite adsorbent by optimizing the ratio of protons (H + ) and lithium ions (Li + ). This tuning adjusts the transport barrier of the flexible 8MRs for C2H4 and C2H6. Ab initio molecular dynamics simulations revealed that Brønsted acid sites (H + ) promote C2H4 diffusion, while Li + ions preferentially hinder C2H6 diffusion. The combination of these effects enhances kinetic selectivity for C2H4. The hindrance by Li + ions also induces the "trapdoor" effect, as illustrated schematically in Fig. .