Adsorption isotherm, differential heat, and sorption mechanism of ammonia on CaA zeolite

Abstract

The article presents the experimentally obtained values of the adsorption isotherm and differential heat of ammonia in CaA zeolite at a temperature of 303 K. The regularity of differential heat with the amount of adsorption, the mechanism of adsorption and the regularity of gradual filling of the zeolite volume of ammonia molecules were determined. Due to the regular change of the differential heat values according to the amount of Na+ and Ca2+ cations in the zeolite, the tetramer 4NH3:Na+ ion-molecular complex is sequentially formed in the first coordination sphere with the sodium cations in the zeolite, then the dimer 2NH3:Сa2+ ion-molecular complex with calcium cations, it was proved that in the second coordination sphere, 2 more ammonia molecules interact with ammonia molecules adsorbed on calcium cations to form a general complex Сa2+:2NH3:2NH3. The differential values of the free energy were calculated from the equilibrium values of the pressure. The adsorption isotherm was recharacterized by the three-state equation of the volumetric micropore filling theory of (VMOT) and it was shown that the theoretically calculated values agree with the experimentally obtained values, and it was also theoretically proved that ammonia forms 4NH3:Na+ and 2NH3:Сa2+ complexes with sodium and calcium cations.