Isotherm and basic thermodynamic characteristics of ammonia adsorption in CsZSM-5 zeolite
Khayot Bakhronov, Oybek Ergashev, Abror Ganiev, Maruf Asfandiyorov, Majidjon Ahkmadov, Kamoliddin Kholikov
Abstract
This paper presents the results obtained by adsorption-calorimetric method of isotherms and basic (ΔH, ΔF and ΔS) thermodynamic characteristics of ammonia adsorption in Cs3,17ZSM-5 zeolite, also the adsorption isotherm described by the equations of the volume filling theory of micropores (TFSM). For measurements of isotherms and differential heat of adsorption, a system consisting of a universal high-vacuum adsorption unit and a coupled differential modified Tian-Calvet type microcalorimeter, DAK-1-1A, was used which directly quantifies and qualifies the nature and forces of adsorption interaction. The correlation between the adsorption-energy characteristics is found and the molecular mechanism of ammonia adsorption in Cs3,17ZSM-5 zeolite in the whole filling region is revealed. Ammonia adsorbed in the Cs3,17ZSM-5 zeolite is located in the first coordination sphere with the Cs+ cation, forming penta-ammonia complexes. It is determined that the average molar entropy of ammonia adsorption on the Cs3,17ZSM-5 zeolite, indicates that in the zeolite the mobility of ammonia molecules is below the liquid phase and close to the mobility of the solid phase, indicating a strong limitation of mobility of ammonia adsorbed on cations.