Surface chemistry

Molecular Adsorption on ceria (110) and (111)

In an effort to further understand the catalytic properties of ceria, we have also studied molecular adsorption of SO2, CO and N2O. SO2 ,which can be serious poison to the ceria surface, chemisorb as a surface sulfate, sulfite or thionite species while CO has been shown to chemisorb as a surface carbonate species. In some of these reactions the surface is either reduced or re-oxidized by the adsorbate. Here, we make use of wave function based methods as well as hybrid DFT and DFT+U functionals to correctly describe the effects of reduction and electron transfer.

Difference electron density of CO chemisorption at ceria(110).
Electron Localization Map of a thionite speices at the CeO2(111) surface.

For N2O, surface reduction does not occur. However, in order to accurately describe the properties of the free N2O molecule, advanced correlation methods are required. Therefore, we also need to go beyond standard DFT functionals in order to correctly describe the N2O-ceria interactions.

A correct description of the electronic properties of reduced ceria using atomic basis-sets requires small-core effective core potentials (ECPs) where 30 electrons are assigned to the valence space of cerium. In order to remove ghost-states, exponents in the contracted Gaussian type orbitals (cGTOs) need to be carefully adjusted. Further information can be found in.

Z. Lu, J. Kullgren, Z. Yang, K. Hermansson. C. Muller, THE JOURNAL OF CHEMICAL PHYSICS 133, 1 (2010)

C.Muller, B Hershend, K. Hermansson, B. Paulus, THE JOURNAL OF CHEMICAL PHYSICS 128, 214701 (2008)

"Physisorption of CO and N2O on Ceria Surfaces", C. Muller .PhD. Thesis, Uppsala University 2009

J. Kullgren, C. W. M. Castleton, C. Muller, D. Munoz Ramo, K. Hermansson,THE JOURNAL OF CHEMICAL PHYSICS 132, 054110 (2010)