Active oxygen center in oxidative coupling of methane on La2O3 catalyst

La2O3 catalyzed oxidative coupling of methane (OCM) is a promising process that converts methane directly to valuable C-2 (ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C-2 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 C-2 products selectivity in OCM over La2O3 catalyst. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press.

Automated summary

La2O3 catalyzed oxidative coupling of methane (OCM) is a promising process for converting methane into valuable C-2 products. Research shows that a carbonate-free surface has higher selectivity and lower light-off temperature, and a new subsurface peroxide structure aids in understanding methyl radicals formation and C-2 products selectivity.