O2 dissociation is an important step for the surface recovery of MoO3 catalyst in the course of oxidation process that involves oxygen vacancy formation and the replenishing.We studied the influence of environmental oxygen on the stability of MoO3(010)and the replenishing process using density functional slab model.Our calculations reveal that O2 dissociates readily on double vacancies that share one Mo atom and the vacancy replenishing most likely occurs on the double vacancies composed of one terminal and a neighboring asymmetrical oxygen vacant site.Under normal experimental conditions the perfect surface MoO3(010)surface is thermodynamically most favorable.In addition,we investigated the defect pattern and found that point defects are unfavorable,compared to the line defect.