Abstract:

Although the rare earth oxide CeO₂-based nano-catalysts have exhibited good performances for the activation of C—H of methane at low temperatures, the nature of the active sites and the C—H activation mechanisms are not clear. In this work, we employed the density functional theory(DFT) method to investigate the activation of C—H of CH₄ and its mechanism at the electroneutral clusters(CeO₂)_m(m=1—3). The results show that the activation of C—H of methane on the clusters obeys the nucleophilic addition modes with the tetra-center structured transition state, in which the electrons are transferred from the clusters to the anti-bonding orbital of CH₄, then weakening and activating the C—H of methane. The bridge oxygen sites of the clusters display the higher activity toward the C—H of methane than the terminal oxygen sites, and the three-fold bridge sites show the greater activity for C—H activation of methane than the two-fold bridge sites. The charge population of the involved Ce and O atoms in the clusters is closely correlated to their ability toward the C—H activation of methane. In addition, not only decreases the solvation of the clusters the energy barrier for C—H activation of methane, but also makes the activity difference between the active sites of the clusters for C—H activation of methane be smaller.

Key words: Ceria, Methane, Density functional theory, Mechanism