Adsorption materials play a key role in determining the efficiency of the pressure swing adsorption process. The selectivity of CO2 over CH4 on most zeolite adsorbents drops dramatically with increasing pressure, and few adsorbents work for CO2/CH4 separation at high pressures. Here, we show that the high selectivity (81) can be retained with our "molecular trapdoor" adsorbent-a potassium exchanged chabazite with an Si/Al ratio of 1, which can selectively admit gas molecules by regulating its cation-kept eight-membered ring (8MR) doorways. Analysis of equilibrium adsorption of CO2 and CH4 showed an exceptionally high selectivity (81) of CO2 over CH4; when the temperature is lower than a threshold value, CH4 molecules cannot access the interior structure of chabazite via K+ blocked 8MRs. We confirmed this characteristic experimentally by adsorption equilibria of CO2 and CH4 up to 10 bar. We investigated the behavior of this adsorbent in a five-step pressure-vacuum swing adsorption (PVSA) cycle to separate CO2 and CH4 from a natural gas stream (15 vol % CO2 balanced with CH4) at a temperature of approximately 293 K and at a feed pressure of 20 bar. The effect of adsorption time on the separation performance was investigated since the adsorbent is known to have kinetic limitations. Our experiments show that the CH4 product with 100% purity and over 90% recovery can be obtained by using the cyclic adsorption process with our novel molecular trapdoor chabazite.