SPECTROSCOPIC STUDIES OF ELECTRON TRAPPING BY SODIUM CATIONIC CLUSTERS IN ZEOLITES

High-energy irradiation of sodium zeolites, both short pulses of 0.4-MeV electrons and steady-state Co-60 gamma-rays, results in the formation of electrons trapped in Na+ clusters, e.g. Na-4(3+), Na-3(2+), and Na2+. ESR spectroscopy is used to identify this species. Only Na-4(3+) is observed in zeolites X and Y at all temperatures; however, other trapped species are observed at low temperatures in zeolite A, e.g. Na-3(2+) and Na2+ as well as Na-4(3+), and in sodalite, Na-4(3+) and Na-3(2+). As the temperature is elevated, the smaller clusters, e.g. Na2+ in zeolite A and Na-3(2+) in sodalite, become less stable. The spectral absorption peaks are approximately 550 nm for Na-4(3+) and approximately 680 nm for Na-3(2+), while the Na2+ Species absorbs in the near-IR regime (>750 nm). The activation energies for hole/electron (Na-4(3+)) neutralization are 12.58 +/- 1.10 kcal/mol (433-469 K) for zeolite Y and 7.10 +/- 0.71 kcal/mol (308-363 K) for zeolite X. In zeolite A, the activation energy for hole/electron (Na-3(2+)) is 15.32 +/- 3.10 kcal/mol (373-421 K), and that for Na2+ is 11.13 +/- 0.91 kcal/mol (253-307 K). The temperature range of the measurements is also given. The rate constant for oxygen quenching of Na-4(3+) in NaX is (3.23 +/- 0.26) x 10(4) Torr-1 s-1, and that of Na-3(2+) in zeolite A is 26.08 +/- 6.42 Torr-1 s-1. The species Na-4(3+) is located inside the supercage of NaX and NaY and in the sodalite cage of zeolite A. In zeolite A, the other two clusters, Na-3(2+) and Na2+, are located in the alpha-cage and sodalite cages, respectively. The G value (i.e., radiolytic yield) of Na-4(3+) in NaY is 2.76 +/- 0.30 for Co-60 gamma-ray irradiation. The study shows the great utility displayed by zeolites is providing unique sites and environments for the creation of new chemical species.