Dependence of Helium Adsorption Energy on the Amount Adsorbed in Na–Y Zeolitic Pores

Isosteric heat of sorption q st and heat capacity C of 3 He and 4 He adsorbed in the 10 Å-diameter pores of Na-Y zeolite have been measured as a function of the amount n adsorbed. q st at T =0 K shows a step-wise decrease with increasing n . This change suggests adsorption potential minima of 0.3 kJ/mol (36 K) in depth on the zeolitic pore wall that is caused by the electric dipole of Na + and (AlO 2 ) - , and shows a first layer completion at n =38% of full pore and multilayers at the larger amount n adsorbed. At \(38 < n {< ~} 70\)% of full pore, one-dimensional gas with C / n ∼4.15 J/K/mol or a liquid state of the second layer on the first solid layer is indicated by the heat capacity, even though the pore diameter is only a few times larger than that of the helium atom.