THERMODYNAMIC CHARACTERISTICS OF WATER ADSORPTION IN AgZSM-5 ZEOLITE

This article presents precision data of isotherms and full thermodynamic characteristics (Delta H, Delta F and and Delta S) of water adsorption in AgZSM-5 zeolite at a temperature of 303 K. For measurements of isotherms and differential heat of adsorption, a system consisting of a universal high-vacuum adsorption unit and a modified differential microcalorimeter of the Tiana-Calve DAK-1-1A type connected to it was used. The differential values of free energy and adsorption entropy are calculated. A correlation was found between the adsorption-energy characteristics and the molecular mechanism of water adsorption in AgZSM-5 zeolite in the entire filling area was revealed. It is determined that small polar water molecules with silver cations in zeolite form a high-energy nano-ion-molecular complex in the first coordination sphere. The entire entropy curve is located below the entropy of liquid water, which indicates a sharp restriction of the mobility of water in the zeolite channels. It is also established that water molecules are adsorbed only in the first and second coordination spheres in accordance with saturation. Adsorption of water molecules in the third coordination sphere was not observed. Starting from the adsorption of similar to 3 mmol/g, a section with a constant adsorption energy of 55 J/mol shows the adsorption of water on homogeneous sections of zeolite channels ZSM-5. These sections can be either straight or zigzag channels. Considering that the dispersion potential in zigzag channels is higher, it can be assumed that adsorption initially proceeds in zigzag channels. After zigzag channels, water molecules are adsorbed into straight channels