Theoretical investigation of the formation of hydrogen peroxide from H2 and O2 over anionic gold clusters Aun- (n=1-4)

The direct synthesis of hydrogen peroxide (H2O2) from H-2 and O-2 over gold nanoparticles has been achieved in the past decade; however, our understanding for the mechanism is still far from complete. We present herein a density functional theory investigation of the formation mechanism of H2O2 from H-2 and O-2 on anionic gold clusters Au-n(-) (n = 1-4). In all cases, the reaction proceeds via two elementary steps: initial H-2 dissociation to form an OOH-containing intermediate and subsequent isomerization of this intermediate into a productlike intermediate. Energetically, the reactions over Au-2(-) and Au-4(-) are significantly less demanding than those over Au- and Au-3(-). In particular, Au- is relatively less active in the hydrogenation of O-2 because the barrier of the rate-determining step is as high as 40.60 kcal mol(-1). The barriers for both the odd- and even-numbered sequences slightly decrease with cluster size. The present results represent a prototype for the direct synthesis of H2O2 from H-2 and O-2 mediated by gold nanoparticles.