Basic energy characteristics and isotherm of methanol adsorption on Cu2+ZSM-5 zeolite

Abstract

This paper presents isotherm results and basic (ΔH, ΔF and ΔS) thermodynamic characteristics of methanol adsorption in Cu2+ZSM-5 zeolite. The trinomial equation of adsorption isotherm by the bulk micropore filling theory (VMOT) is also described. A correlation between adsorption-energy characteristics was found and molecular mechanisms of methanol adsorption in Cu2+ZSM-5 zeolite were revealed in the whole filling region. It was determined that Cu2+ cations are located in shielded positions of the crystal lattice of zeolite ZSM-5. Adsorption of methanol molecule leads to the migration of Cu2+ cations from the zeolite lattice to the crossings formed by the intersection of straight and zigzag channels and to the formation of ion/molecular complexes of different multiplicity in them. It was found that small polar methanol molecules form high-energy hepta complexes with Cu2+ cation and are located in the first coordination sphere in Cu2+ZSM-5 zeolite. It was determined that the average molar entropy (-65 kJ/mol) of methanol adsorption indicates that in the zeolite the mobility of methanol molecules is lower than the liquid phase and close to the mobility of the solid phase.