Spectroscopic studies of sol-gel Li/MgO catalysts

Samples of Li/MgO were generated by co-gelling Li2CO3 and Mg(OEt)(2), and c haracterized with the aid of diverse spectroscopic techniques: EPR, FTIR, U V-vis, TGA, DTA, and X-ray powder diffraction (with refinement of the cryst alline structure). The presence of the EPR hyperfine structure of Mn4+ resu lting from the conversion of the unintentionally present impurity Mn2+ to M n4+, establishes clear evidence that lithium ions are present in the sol-ge l matrix substituting for magnesium ions. Indeed, only after irradiating th e sample with gamma rays at liquid nitrogen, the formation of [Li](0) cente rs in a metastable fashion was possible, but further instability and annihi lation occurred when the sample was brought back to room temperature. The s ol-gel material described in this work proves to be active in the oxidative coupling of methane.