The conventional synthesis of hydrogen peroxide(H2O2) confronts intense energy cost, tedious separation procedures and high cost, which is not competitive to the traditional oxidants. Hence, the direct synthesis of H2O2 from hydrogen and oxygen has attracted intense interest, in which the appropriate catalyst is the determining factor. Most research agreed that the determining reaction in direct synthesis of H2O2 will be the absorbed hydrogen atoms reacting with absorbed oxygen molecules as the following:
Previous works on transition metal such as Pd, Au and related alloy have proved that a high H2O2 selectivity can only achieved through low rate O-O bond cleavage meantime high reaction rate of adding hydrogen atoms to absorbed oxygen molecules [1, 2]. Moreover, the absorption energy of H2O2 also should not be too negative to ensure desorption of formed H2O2 for higher productivity and selectivity. Comparing to wide applications in many organic reactions, Ru and Ni as important catalysts have been rarely studied in the synthesis of H2O2.
In this work, we propose the mechanism of RuNi alloy as a novel catalyst in direct synthesis of H2O2 through density functional theory (DFT) calculations. Hydrogen is highly possible to break on this surface with lowest energy barrier on top of Ni site. The catalyst shows different behaviours with or without oxygen coverage. Partially oxygen coverage can significantly decrease the energy barrier for oxygen absorption and the possibility of oxygen cleavage, which both benefits the further reaction of absorbed oxygen with dissociative hydrogen atoms to form H2O2. Moreover, the dissociation of formed H2O2 on the surface are also supressed. The absorption energy of formed H2O2 on the surface is reasonable to prevent over-binding of H2O2 and affect the productivity. In this alloy, Ru is relatively unstable and more active to react with absorbed molecules. Ni can play a role as balancing the binding energy to prevent over electron transfer to achieve high selectivity of H2O2. Therefore, this novel alloy RuNi shows high potential for direct synthesis of H2O2.
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