Reactivity of metal oxide clusters with hydrogen peroxide and water – a DFT study evaluating the performance of different exchange–correlation functionals

Abstract

We have performed a density functional theory (DFT) investigation of the interactions of H₂O₂, H₂O and HO radicals with clusters of ZrO₂, TiO₂ and Y₂O₃. Different modes of H₂O adsorption onto the clusters were studied. In almost all the cases the dissociative adsorption is more exothermic than molecular adsorption. At the surfaces where H₂O has undergone dissociative adsorption, the adsorption of H₂O₂ and the transition state for its decomposition are mediated by hydrogen bonding with the surface HO groups. Using the functionals B3LYP, B3LYP-D and M06 with clusters of 26 and 8 units of ZrO₂, the M06 functional performed better than B3LYP in describing the reaction of decomposition of H₂O₂ and the adsorption of H₂O. Additionally, we investigated clusters of the type (ZrO₂)₂, (TiO₂)₂ and (Y₂O₃) and the performance of the functionals B3LYP, B3LYP-D, B3LYP*, M06, M06-L, PBE0, PBE and PWPW91 in describing H₂O₂, H₂O and HO˙ adsorption and the energy barrier for decomposition of H₂O₂. The trends obtained for HO˙ adsorption onto the clusters are discussed in terms of the ionization energy of the metal cation present in the oxide. In order to correctly account for the existence of an energy barrier for the decomposition of H₂O₂, the functional used must include Hartree–Fock exchange. Using minimal cluster models, the best performance in describing the energy barrier for H₂O₂ decomposition was obtained with the M06 and PBE0 functionals – the average absolute deviations from experiments are 6 kJ mol⁻¹ and 5 kJ mol⁻¹ respectively. With the M06 functional and a larger monoclinic (ZrO₂)₈ cluster model, the performance is in excellent agreement with experimental data. For the different oxides, PBE0 was found to be the most effective functional in terms of performance and computational time cost.