Differential entropy and thermokinetics of ammonia molecule adsorption on CaA zeolite (M-22)

Abstract

In This paper presents the results of differential entropy and adsorption equilibrium establishment time as a function of the magnitude of ammonia adsorption in zeolite CaA (M-22) at a constant temperature of 303 K. To measure the thermokinetics of adsorption, a system consisting of a universal high-vacuum adsorption apparatus coupled to a Tian-Calvet type differential microcalorimeter, DAC-1-1A, was used. A correlation between adsorption-energy and thermokinetic characteristics was found, and the molecular mechanism of ammonia adsorption in CaA (M-22) zeolites in the whole filling region was also revealed. A stepwise change in the differential entropy and thermokinetics of adsorption depending on the amount of sodium and calcium cations in the zeolite was found. Ammonia molecules initially form tetrameric ion-molecular complexes 4NH3:Na+ in the first coordination sphere with sodium cations and dimeric ion- molecular complexes 2NH3:Ca2+ with calcium cations. The average molar integral entropy of ammonia adsorption on zeolite CaA (M-22) was found to be -71 J/mol- K and indicates that in the zeolite the mobility of ammonia molecules is lower than the liquid phase and close to the solid phase mobility, leading to a strong inhibition of the mobility of adsorption on ammonia cations.