For the recovery of high purity CO2, two adsorbents, zeolite 13X and activated carbon, are examined. Pressure swing adsorption (PSA) cycle simulations are performed to compare the performance of different adsorbents in separation from two feed mixtures : 16/84 (v/v) CO2/N-2 and 26/74 CO2/N-2. Despite high-temperature excursions in the adsorption step, zeolite 13X is a better adsorbent than activated carbon in nonisothermal, adiabatic PSA process due to favorable isotherm shape and equilibrium selectivity. Moreover, a higher temperature excursion for 13X during the product (CO2) purge step reduces the purge gas amount and this actually helps PSA performance. High purity of CO2 (over 99%) can be produced by zeolite 13X at higher recoveries (53% from low-CO2-concentration flue gas and 70% from high-CO2-concentration flue gas) and higher productivities than carbon. In selecting an appropriate adsorbent, high working adsorption capacity, high equilibrium selectivity, and low purge gas requirement dominate the separation by PSA process whereas the heat effects play a secondary role. A simple criterion is proposed for a priori adsorbent selection.