Electron spin resonance studies of methyl radicals trapped on 4A type zeolite

Abstract

Three kinds of methyl radicals were observed with different heat treatments of Linde 4A type zeolite. The first is the normal methyl radical; the second is the abnormal methyl radical, type I, having additional coupling with one extra proton; and the third is the abnormal methyl radical, type II, having large coupling with one of the three protons. These three different radicals are stabilized on the zeolite heat treated at ca. 65, ca. 80, and ca. 250$sup 0$C, respectively. It was revealed by experiments using CD$sub 4$ that a hydrogen atom liberated from irradiated CH$sub 4$ is most probably stabilized on the zeolite surface and converted into H$sup +$, which causes the additional coupling noted in the abnormal methyl radical I. The fact that the $sup 13$C-hyperfine coupling of the abnormal methyl radical, type II, gives axial symmetric tensors and shows a trend of A/sub parallel/ (75.8 G) greater than A/sub perpendicular to/ (10.5 G) indicates that this methyl radical interacts with the surface through a 2P/sub pi/ unpaired-spin orbital and rotates about the C$sub 3$ symmetry axis. The relation of each type of methyl radical with the trapping environment as well as the probable geometry of each radical ismore » discussed. (auth)« less