Sorption in partially hydrated NaA and CaA zeolites

Abstract

An attempt was made to clarify the adsorption mechanism of partially hydrated NaA and CaA zeolites. The sorption of CO, CO₂ and CH₄ in the CaA and NaA zeolites was investigated as a function of the outgassing temperature, using differential thermal analysis, equilibrium thermal analysis and adsorption techniques. Important adsorption variations depending on the nature of the entering gases were observed at low water coverages. Shielding effects of water molecules around the exchangeable cations were shown to be responsible for this phenomenon. At higher water coverages another adsorption change appears in the CaA zeolite. This change in adsorption was independent of the entering gases and can be explained by the blocking effects of water molecules in the large zeolitic cavities. The variation of the isosteric heats of adsorption in the CaA zeolite as a function of the water loading supports the conclusions from the sorption data.