Heats of Adsorption of Polar and Non-Polar Gases in Homogeneous and Heterogeneous Adsorbents
We have designed and constructed a Tian-Calvet type microcalor-imeter for the simultaneous determination of adsorption isotherms and differential heats of adsorption. The adsorption of a series of gases with different values of polarizability, polarity, and molecular diameter has been studied on both homogeneous (silicalite) and heterogeneous (Na-ZSM-5 and NaX) adsorbents. Heats of adsorption of non-polar gases (SF6, C2H6, CH4, O2, Ar) increase in the order NaX < silicalite < Na-ZSM-5; heats of adsorption of polar gases (N2 and CO2) increase in the order silicalite < Na-ZSM-5 < NaX. The heat profiles of the polar gases show a steep decrease with coverage on NaX and Na-ZSM-5 corresponding to the filling of high-energy sites adjacent to sodium cations.
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