Reduction and fragmentation of CS2 at the surface of electron-rich MgO: an EPR study

Sulfur contamination of alkaline earth oxide surfaces has important consequences in many fields of chemistry, such as surface science and catalysis. We used the Electron Paramagnetic Resonance (EPR) technique to study the interaction of CS₂ molecules under different pressure and temperature conditions, with the bare and electron-enriched surface of MgO. CS₂ reacts on the oxide surface through two distinct reaction paths, one leading to diamagnetic species, the other to paramagnetic surface entities. Both these reaction paths lead to the fragmentation of the CS₂ molecule and, in some cases to oligomerization processes. EPR experiments allowed to follow the formation of the unstable CS ₂ ⁻ radical intermediate and its evolution through formation of several surface radicals like S⁻, S ₃ ⁻ and S _n ⁻ (n ⩾ 3), depending on the reaction conditions.     

The interaction between hydrogen peroxide and metal oxides: EPR investigations

The interaction of hydrogen peroxide with various metal oxides has been followed by EPR in the aim of investigating the paramagnetic species formed along the complex processes of H₂O₂ decomposition and interaction with the oxide. Data are reported about three systems (MgO, ZrO₂ and Me²⁺/Y zeolite) which are representative of three classes of oxides (insulators, semiconductors and aluminosilicate molecular sieves). Several radical species have been put into evidence in the various cases. The superoxide O ₂ ^? ion has been observed in all cases while in the case of MgO also the OH radical and the O^? radical ion have been identified. In the case of Zn²⁺/Y zeolite, beside the superoxide radical anion, a new signal is observed which shows up upon treating the sample at 640 K and which is preliminarily assigned to a species in the triplet state in the zeolitic cavity.