In situ Raman spectroscopy of peroxide ions on barium/magnesium oxide catalysts

Abstract

In situ Raman spectroscopy has been used to show that peroxide ions are present on Ba/MgO catalysts at temperatures up to 800 OC. The surface 0z2ions are believed to be responsible for the activation of CH4 during the oxidative coupling reaction which occurs at these elevated temperatures. At 100 OC the peroxide ion spectrum is characterized by a major line at 842 cm-l, with minor peaks at 829 and 821 cm-l. As the temperature was increased, all of the peaks shifted to lower wavenumbers and broadened, until at 800 OC only a broad asymmetric band remained. Introduction of l 8 0 z also caused the peaks to shift to lower wavenumbers, consistent with the assignment of the spectra to peroxide ions. In the presence of COz and H20 the 0z2ions reacted to form carbonate ions at T 1 500 OC, which is in agreement with the poisoning effect of C02 in the catalytic experiments. At Ba loadings 5 2 mol ?6 a two-dimensional layer of BaOz is present on the surface of MgO, but at larger loadings crystallites of BaOz contribute significantly to the Raman spectra. e Abstract published in Aduance ACS Absrracrs. November 15, 1993.Estonia.

Isotopic Oxygen Exchange and EPR Studies of Superoxide Species on the SrF2/La2O3 Catalyst

“…The frequency shift with respect to temperature is a well-known phenomenon of solids relating to the lattice relaxation at high temperature. Similar effect was also observed in the in situ Raman spectroscopy of the peroxide ions on the Ba/MgO catalyst [10].…”

“…Otsuka et al found that Na 2 O 2 , SrO 2 and BaO 2 were capable of converting CH 4 into C 2 H 6 at temperature below 673 K in the presence of O 2 [9]. Lunsford et al detected a major Raman peak at 842 cm -1 , which was ascribed to the O-O stretching mode in BaO 2 over the 0.5 mol% Ba/MgO catalyst [10]. X-ray photoelectron spectroscopy (XPS) on the same catalysts showed a good correlation between the near-surface concentration of the peroxide ions and the intrinsic catalytic activity [11].…”

Performance Improvement of NO x -Storage BaO/Al2O3 by Using Barium Peroxide as the Precursor of BaO

“…Al 2 O 3 support did not have any Raman band, which confirms its cubic c-Al 2 O 3 phase [11] and is in line with XRD results. The BaO 2 -80 showed a sharp band at 842 cm -1 due to the O-O stretching vibration of peroxide species (O 2 2-) in BaO 2 crystals [12]. The three BaO/Al 2 O 3 -550 materials showed Raman bands at 1,058 and 690 cm -1 , which are assigned to the d mode and the A 1 ' symmetric stretching mode of the carbonate ions, respectively [12].…”

Theoretical Study on the Mechanism of the Reaction of CH4 + MgO

“…1 The partial oxidation and oxidative coupling of methane, in particular, have attracted considerable attention. [2][3][4][5][6][7][8][9] Many metal oxide catalysts have been used for these reactions, 2,[10][11][12] and MgO has been found to be one of the most effective catalysts. 12,13 To understand the nature of the interaction between methane and MgO, the adsorption and dissociation of methane on MgO catalyst have been extensively investigated experimentally.…”