A series of pyrazine-interior-embodied metal-organic framework-74 composites (py-MOF-74) were successfully synthesized by a post-synthetic vapor modification method. Here, pyrazine molecules occupy the cavity to block the wide pores of MOF-74, which accentuates the difference in adsorption of a pair of gases on MOFs and consequently reinforces the adsorption selectivity. Different from the "physical confinement" of occupants, the pyrazine molecule with dual "para-nitrogen" atoms donates one N atom to bond with the open metal ion of MOF-74 for stability and the other N atom for potential CO 2 trapping. Typically, py-MOF-74c with the highest pyrazine insertion ratio displays selectivity greatly superior to that of MOF-74 in equimolar CO 2 /CH 4 (598 vs. 35) and in simulated CO 2 /N 2 flue gas (471 vs. 49). Py-MOF-74 entities are long-lived adsorbents, and their CO 2 capacity can be maintained even after storage for 1 year in air. Py-MOF-74 also showed a sharp molecular sieve property in fixed-bed cycle adsorption tests, which implies its great potential in real applications.