上海科技大学知识管理系统

La₂O₃ catalyzed oxidative coupling of methane (OCM) is a promising process that converts methane
directly to valuable C₂ (ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C₂ products, and a lower light-off temperature as well. Further study is focused on carbonate-free La₂O₃ catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 eV correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results, DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexacoordinate lattice oxygen sites, with energy 2.18 eV lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C₂ products selectivity in OCM over La₂O₃ catalyst.