Tatsuo Masuda

Infrared and calorimetric studies of adsorbed carbon dioxide on NaA and CaNaA zeolites

Abstract Adsorption properties of carbon dioxide on NaA and Ca-exchanged A zeolites were examined by measurements of infrared spectra and differential heats of adsorption. Carbon dioxide was adsorbed chemically on NaA at 25°C by the formation of stable carboxylate species which were not observed on CaNaA. The 12th Na + ion located at the site S III seemed to be responsible for the chemisorbed species of carbon dioxide on NaA. The heat of their formation was thus estimated to be about 86 kJ/mole. On CaNaA greater than 46% exchanged with Ca 2+ ions, the carbonate species were observed and remained even after evacuation at 400°C. The initial heats of adsorption of carbon dioxide observed on CaNaA showed fairly good agreement with the values calculated by using the electrostatic field gradients which were determined from nitrogen adsorption.

Calorimetric evidence for nonspecific and specific interactions of several gases with surfaces of NaA and CaNaA zeolites

Abstract The differential heats of adsorption (q) of simple molecules on NaA and CaNaA zeolites were measured. Initial heats of adsorption increased with the degree of Ca-exchange and in the order of heats of adsorption was: CO > N2 > CH4 > Ar > H2. The qs for H2, Ar, and CH4 change almost linearly with their polarizabilities (α). On the other hand, plots of the heats of adsorption of N2 and CO fell above the characteristic q − α curve. Electrostatic field gradients evaluated from the specific interaction energy of N2 with the surfaces of NaA and CaNaA increased monotonically with the degree of Ca-exchange. The heats of adsorption of CO on NaA and CaNaA calculated by using the electrostatic field gradients showed fairly good agreement with the experimental values, indicating that N2 and CO molecules are adsorbed energetically and in a similar way and at almost similar positions in the A-type zeolite.