ESR Studies of Oxygen, Sulfur Oxide, and Sulfur Radicals Adsorbed on NaX Zeolite

Abstract

Abstract The states of O2 and SO2 adsorbed on NaX zeolite were investigated by means of ESR. No oxygen anion radicals were formed thermally on NaX up to 773 K. The adsorption of O2 on γ-irradiated NaX in a vacuum, however, resulted in an ESR spectrum due to O2−. Several kinds of O2− species and O3− were found to be formed on NaX by γ-irradiation in the presence of O2. These oxygen anion radicals showed different reactivities with N2O, ethylene and propylene, and transferred electrons to SO2 to form SO2−. The SO2− radical was also produced on NaX by raising the temperature from 298 to 573 K after the introduction of SO2. This reacted with O2 to form a radical, like SO4−, but upon evacuating the O2, the reaction was reversed to give the original SO2−. When the temperature of NaX was further raised to 773 K in the presence of SO2, a spectrum assigned to a polyatomic sulfur radical appeared indicating that SO2 decomposition occurred at high temperature. This polymer radical was stable in an O2 atmosphere at room temperature.