  We present an ab initio investigation of the interaction between methane, its
dehydrogenated forms and the cerium oxide surface. In particular, the
stoichiometric CeO2(111) surface and the one with oxygen vacancies are
considered. We study the geometries, energetics and electronic structures of
various configurations of these molecules adsorbed on the surface in vacuum,
and we extend the analysis to realistic environmental conditions. A phase
diagram of the adsorbate-surface system is constructed and relevant transition
phases are analyzed in detail, showing the conditions where partial oxidation
of methane can occur.
