Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces

Abstract

We performed an experimental and density functional theory (DFT) investigation of the reactions of H 2 O 2 with ZrO 2, TiO 2, and Y 2 O 3 . In the experimental study we determined the reaction rate constants, the Arrhenius activation energies, and the activation enthalpies for the processes of adsorption and decomposition of H 2 O 2 on the surfaces of nano- and micrometer-sized particles of the oxides. The experimentally obtained enthalpies of activation for the decomposition of H 2 O 2 catalyzed by these materials are 30 ± 1 kJ·mol –1 for ZrO 2, 34 ± 1 kJ·mol –1 for TiO 2, and 44 ± 5 kJ·mol –1 for Y 2 O 3 . In the DFT study, cluster models of the metal oxides were used to investigate the mechanisms involved in the surface process governing the decomposition of H 2 O 2 . We compared the performance of the B3LYP and M06 functionals for describing the adsorption energies of H 2 O 2 and HO • onto the oxide surfaces as well as the energy barriers for the decomposition of H 2 O 2 . The DFT models implemented can describe the experimental reaction barriers with good accuracy, and we found that the decomposition of H 2 O 2 follows a similar mechanism for all the materials studied. The average absolute deviation from the experimental barriers obtained with the B3LYP functional is 6 kJ·mol –1, while with the M06 functional it is 3 kJ·mol –1 . The differences in the affinity of the different surfaces for the primary product of H 2 O 2 decomposition, the HO radical, were also addressed both experimentally and with DFT. With the experiments we found a trend in the affinity of HO • toward the surfaces of the oxides, depending on the type of oxide. This trend is successfully reproduced with the DFT calculations. We found that the adsorption energy of HO • varies inversely with the ionization energy of the metal cation present in the oxide.