: _ NaX has a higher affinity for CO2 and CH4 than NaY has.
_ NaY exhibits higher maximum adsorption capacity compared with NaX.
_ Both NaX and NaY present a heterogeneous surface.
_ Adsorbed CO2 and CH4 are in ordered arrangement in both NaX and NaY.
_ Adsorbed CO2 and CH4 have more orderly arrangement in NaX than in NaY.