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A dimer model Pd₂ was established to study the adsorption of CH_x (x = 1−4) and CH₄ dehydrogenation, as well as syngas formation using density functional theory (DFT) at the atomic level. Meanwhile, insight into understanding the role of the oxygen atom on the partial oxidation of methane (POM) was also calculated based on a trimer model of Pd₂O. For the adsorption of CH_x, results showed that the presence of an oxygen atom was a disadvantage to the adsorption of CH_x (x = 1−3) species. For CH₄ dissociation, the process of CH₂→CH + H was found to be the rate-limiting step (RSD) on both Pd₂ and Pd₂O. H₂ was formed by the reaction of CH₂ + 2H→CH₂ + H₂. For CO formation, it was primarily formed in the process of CH + O→CHO→CO + H on both the Pd₂ and the Pd₂O catalyst. Thermodynamic and kinetic calculations revealed that formation and maintainance of the oxygen atom on the Pd surface could promote a POM reaction to achieve high H₂ and CO yield and selectivity. Our study provides a helpful understanding of the effect of an adsorbed oxygen atom on a POM reaction with a Pd catalyst.