Characterization of Electron Deficient Oxide Ion of Heat Treated MgO for Activation of Methane

• Published in: Bulletin of the Chemical Society of Japan 1998-08, Vol.71 (8), p.1999-2003
• Main Authors: Karasuda, Takashi, Aika, Ken-ichi
• Format: Article
• Language: English
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.71.1999

Electron deficient oxide ions on the heat-treated MgO were characterized by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and other methods (electron spin resonance (ESR) and Fourier transform infrared spectroscopy (FT-IR)). The O1s XP spectrum of MgO evacuated at 873 K has a very small shoulder peak (533.8 eV) at the higher binding energy (BE) side of the O2− peak (at 531.5 eV). Upon the evacuation of 973 K, this shoulder peak increased remarkably, and at the same time H2 started to be evolved (TPD). Since H2 must be produced from a dissolved water in the bulk or surface OH without forming O2, the surface oxygen must have a charge lower than 2. Thus, the shoulder peak was assigned to O−. This state was not observable by ESR and not reactive to methane at room temperature (FT-IR), while O− produced on the UV-irradiated MgO was ESR-observable and reactive. However, the heat-treated surface O− must react with methane during the oxidative coupling of methane (OCM) reaction at 973 K. The two kinds of states for O− on MgO are discussed from the standpoint of the defect chemistry.