The CO2 equilibrium adsorption and breakthrough activity of CO2-NO2 mixtures on A- and faujasite-type zeolites and Na- and proton-type (HM) mordenites were studied to determine the appropriate zeolite for separation of low-concentration mixtures of CO2 and NO2. Adsorption of CO2 correlated with the polarity of the zeolites as a result of dominant adsorption via interaction of the quadrupole moment and polar surface sites. Competitive adsorption of NO2 and CO2 gives nearly zero breakthrough times for CO2 on 5A- and faujasite-type zeolites and HM. Adsorption separation of CO2 and NO2 by zeolites depends on the NO2 adsorptivity, which is determined not only by surface polar sites but also by pore geometry and dimension. 13X had the greatest NO2 adsorptivity, but the thermal instability in NO2 adsorptive sites is the main obstacle for its use as a substrate for the separation of CO2 and NO2. Sufficient protonation of NaM leads to zero CO2 adsorption and still keeps a great NO2 adsorption. Because of the thermal stability and low NO2 desorption temperature, HM is the most promising adsorbent for separation of CO2 and NO2 using the thermal-swing adsorption method.
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