ELECTRON TRAPPING BY SODIUM-CATION CLUSTERS IN ZEOLITES - EFFECTS OF SI/AL RATIO AND FOREIGN SPECIES

The effects of the Si/Al ratio, electron scavenging ions such as Cu2+, Co2+, Ni2+, Zn2+, Pb2+, and Tl+, and n-pentane on electron trapping by sodium cation clusters in zeolite faujasite under gamma-irradiation at room temperature are studied. The results show that as the Si/Al ratio increases, the absorption band of Na-4(3+) trapped electrons shifts toward shorter wavelengths and becomes narrower, the oxygen quenching rate constant for the Ni-4(3+) trapped electrons decreases, and the activation energy increases. n-Pentane interacts with the electronic hole and enhances the yield of Na-4(3+) trapped electron. The electron scavenging ions compete with the Na-4(4+) electron trapping sites, and the quenching of the Na-4(3+) trapped electrons is static in nature except for Tl+. Here the Tl+ ion increases the initial yield of the Na-4(3+) trapped electrons and concomitantly fosters a faster decay of the trapped electrons. According to the quenching kinetics, these ions are grouped into four categories: those reacting with thermalized electrons (Cu2+, Cd2+, Ni2+), those with quazifree electrons (Zn2+, Pb2+), those with both stares of the electrons (Co2+), and those with trapped electrons (T1(+)).