Basic energy characteristics and isotherm of methanol adsorption on Cu<sup>2+</sup>ZSM-5 zeolite
Oybek Ergashev, Khayot Bakhronov, Khamid Kholmedov, Abror Ganiev, Khasan S. Karimov, Sarvar Khalilov
Abstract
This paper presents isotherm results and basic (Δ H , Δ F and Δ S ) thermodynamic characteristics of methanol adsorption in Cu 2+ 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 Cu 2+ ZSM-5 zeolite were revealed in the whole filling region. It was determined that Cu 2+ cations are located in shielded positions of the crystal lattice of zeolite ZSM-5. Adsorption of methanol molecule leads to the migration of Cu 2+ 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 Cu 2+ cation and are located in the first coordination sphere in Cu 2+ 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.