Dissociative adsorption of methane on the Cu and Zn doped (111) surface of CeO2

• A +U correction is necessary on the Cu dopant 3d states to correctly describe the electronic structure for Cu-CeO2.
• Charge compensating oxygen vacancies are necessary in divalent doping of CeO2 (111).
• Cu and Zn doping enhance the reducibility and the interaction with H and CH3+H, which is related to the dopant coordination.
• Cu-CeO2 does not lower the dissociation barrier compared to the undoped CeO2 surface as significantly as Zn-CeO2.
• Zn-CeO2 is a superior catalyst for methane activation.

The development of economical heterogeneous catalysts for the activation of methane is a major challenge for the chemical industry. Screening potential candidates becomes more feasible using rational catalyst design to understand the activity of potential catalysts for CH4 activation. The focus of the present paper is the use of density functional theory to examine and elucidate the properties of doped CeO2. We dope with Cu and Zn transition metals having variable oxidation state (Cu), and a single oxidation state (Zn), and study the activation of methane. Zn is a divalent dopant and Cu can have a +1 or +2 oxidation state. Both Cu and Zn dopants have an oxidation state of +2 after incorporation into the CeO2 (111) surface; however a Hubbard +U correction (+U = 7) on the Cu 3d states is required to maintain this oxidation state when the surface interacts with adsorbed species. Dissociation of methane is found to occur locally at the dopant cations, and is thermodynamically and kinetically more favorable on Zn-doped CeO2 than Cu-doped CeO2. The origins of this lie with the Zn(II) dopant moving towards a square pyramidal geometry in the sub surface layer which facilitates the formation of two-coordinated surface oxygen atoms, that are more beneficial for methane activation on a reducible oxide surface. These findings can aid in rational experimental catalyst design for further exploration in methane activation processes.

Figure optionsDownload as PowerPoint slide