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 micrometersized 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.

The kinetics, mechanism, and activation energy of H2O2 decomposition in ZrO2 particle suspensions were studied. The obtained first-order and second-order rate constants for the decomposition of H2O2 in the presence of ZrO2 at T = 298.15 K produced the values k 1 = (6.15 ± 0.04) × 10−5 s−1 and k 2 = (2.39 ± 0.09) × 10−10 m·s−1, respectively. The dependency of the reaction first-order rate constant with temperature was studied; consequently, the activation energy for the reaction was obtained in the temperature interval 294.15−353.15 K having yielded the value E a = 33 ± 1.0 kJ·mol−1. The dependency of the zeroth-order reaction rate constant with pH was investigated and discussed. A mechanistic study encompassing the investigation of the dynamics of formation of hydroxyl radicals during the course of the reaction was performed. A version of the modified Hantzsch method was applied for this purpose, and it was verified that the dynamics of formation of hydroxyl radicals during the reaction are in good agreement with the proposed reaction mechanism.

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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.

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The standard molar enthalpies of sublimation of ferrocene, 1,1'-dimethylferrocene, decamethylferrocene, ferrocenecarboxaldehyde and alpha-methylferrocenemethanol, and the enthalpy of vaporization of N,N-dimethyl(aminomethyl)ferrocene, at 298.15 K, were determined by Calvet-drop microcalorimetry and/or the Knudsen effusion method. The obtained values were used to assess and refine our previously developed force field for metallocenes. The modified force field was able to reproduce the deltasubHdegreesm and deltavapHdegreesm values of the test-set with an accuracy better than 5 kJ.mol-1, except for decamethylferrocene, in which case the deviation between the calculated and experimental deltasubHdegreesm values was 16.1 kJ.mol-1. The origin of the larger error found in the prediction of the sublimation energetics of decamethylferrocene, and which was also observed in the estimation of structural properties (e.g., density and unit cell dimensions), is discussed. Finally, the crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)] at 293 and 150 K, respectively, are reported.

We used density functional theory to investigate the sequential oxidation of the (110) surface of fcc copper triggered by the dehydrogenation of molecularly adsorbed water-the reactions studied did not involve any oxygen besides that present in the water molecule. According to the obtained Gibbs free energies, the formation of half a monolayer of HO and the corresponding amount of hydrogen gas is spontaneous (∆ r G • <0) starting from a monolayer of adsorbed water at Cu(110). The subsequent dehydrogenation steps necessary to ultimately form one monolayer of O atoms are non-spontaneous (∆ r G • >0). We present a computationally efficient approach which shows good accuracy for determining the solvation energy of the Cu (110) surface, deviating only by 0.014 eV from literature data. The solvation effect imparts additional stabilization to several oxygen containing species adsorbed at the Cu(110) surface.Additionally, we investigated the effect of an overlayer of water molecules at the surface where the dehydrogenation of H 2 O takes place. We found that even though the Gibbs free energy changes associated with the first steps of dehydrogenation of H 2 O at the Cu surface do not differ substantially from those without an additional water layer, subsequent dehydrogenation steps are favored by as much as 1.6 eV. In view of these results we discuss the importance of the hydrogen bonding network-formed when an overlayer of H 2 O is present-in determining the reactivity of surface species. Additionally, we found a considerable effect of the second water layer on the surface relaxation, which differs significantly from the case where no second water layer is present. The hydrogen bonding network has an important role in affecting the chemistry of the surface species but also in stabilizing the surface itself, which in turn affects the surface relaxation. These findings shed additional light on the modeling of surface processes in solution, which have implications for corrosion science and catalysis.

Presently and for the foreseeable future, hydrogen peroxide and transition metal oxides are important constituents of energy production processes. In this work, the effect of the presence of HO radical scavengers on the product yield from the decomposition of H2O2 on metal oxide surfaces in aqueous solution was examined experimentally. Scavenging the intermediate product HO˙ by means of Tris or TAPS buffer leads to enhanced formation of H2. In parallel, a decrease in the production of the main gaseous product O2 is observed. Under these conditions, H2 formation is a spontaneous process even at room temperature. The yields of both the H2 and O2 depend on the concentration of Tris or TAPS in the reaction media. We observed that TAPS has a higher affinity for the surface of ZrO2 than does Tris. The difference in adsorption of both scavengers is reflected by the difference in their influence on the product yields. The observed sensitivity of the system H2O2-ZrO2 towards the two different scavengers indicates that O2 and H2 are formed at different types of surface sites.