Density-functional studies of hydrogen peroxide adsorption and dissociation on MoO3(100) and H0.33MoO3(100) surfaces

Abstract

Hydrogen peroxide (H₂O₂) adsorption and dissociation mechanisms on MoO₃(100) and H_0.33MoO₃(100) surfaces were studied by means of density-functional computations. Mechanisms were examined on both fixed and relaxed clusters. On both fixed and relaxed molybdenum oxide clusters, H₂O₂ adsorbs molecularly and does not dissociate. However, on the surface of both the fixed and relaxed molybdenum hydrogen bronze (H_0.33MoO₃) clusters, H₂O₂ can dissociate through a pathway involving either H–O or O–O bond cleavage. The barrier for direct H–OOH dissociation is 39.9 kJ mol⁻¹, leading to an adsorbed H atom and a HOO group. The dissociation of the O–O bond leads to the most energetically stable products, two OH species bound to the surface molybdenum atoms with the relative adsorption energy −430.4 kJ mol⁻¹. The mechanism on the relaxed cluster is slightly more complex due to additional stability of the molecularly adsorbed structure and ability to form a geminal intermediate not found on the fixed cluster. On both the relaxed and fixed clusters, hydrogen cleavage is kinetically favoured. Chemical reaction on the molybdenum hydrogen bronze surface is made possible by the increased electron density at the surface with respect to the oxide due to the contribution from the HOMO orbital.