Energy Distribution of Ethylene Adsorption and Calcium Ion Positions in A-type Zeolites

Differential molar heats of adsorption of ethylene were calorimetrically determined on Na-A, Ca-Na-A, and Ca-A type zeolites and the molar entropy change accompanied by adsorption was caluclated. The adsorption energy distribution was calculated by an iterative simulation of differential molar heats of adsorption according to the method previously developed. The Ca ion exchange in A-type zeolites results in the formation of a strong electrostatic field which interacts with π electrons of ethylene. The distribution was found to be homogeneous in Na-A, while several steps were observed in Ca-Na-A zeolites depending on the degree of Ca-exchange. The energy values of these steps and the variation in the adsorption energy with the coverage reflect the cation distribution in the zeolite framework.