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  • 1.
    Diesen, Veronica
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lousada, Claudio
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    A hydrogen sulfate salt of chlordiazepoxide2012In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 68, no 7, p. o2091-o2092Article in journal (Refereed)
    Abstract [en]

    Crystals of the hydrogen sulfate salt of chlordiazepoxide (systematic name: 7-chloro-Nmethyl-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepin-2-iminium 4-oxide hydrogen sulfate), C 16H 15ClN 3O +·HSO 4 -, were obtained from a solution of chlordiazepoxide and sulfuric acid in methanol. The structure features chlordiazepoxide molecules that are protonated at the imine N atom. The seven-membered ring adopts a boat conformation with the CH 2 group as the prow and the two aryl C atoms as the stern. The dihedral angle between the benzene rings is 72.41 (6)°. In the crystal, the HSO 4 - anion acts as a bridging group between two chlordiazepoxide cations. The H atom of the protonated imino N forms an N - H⋯O hydrogen bond with a hydrogen sulfate ion. The anion in turn forms two hydrogen bonds, O - H⋯O with the anion as donor and N - H⋯O with the anion as acceptor, to generate an R 2 2(10) loop. Each HSO 4 - anion connects two chlordiazepoxide moieties of the same chirality.

  • 2.
    Ghadami Yazdi, Milad
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Evertsson, J.
    Rullik, L.
    Soldemo, Markus
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Bertram, F.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Weissenrieder, J.
    Lundgren, E.
    Göthelid, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Structure dependent effect of silicon on the oxidation of Al(111) and Al(100)2019In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 684, p. 1-11Article in journal (Refereed)
    Abstract [en]

    The effect of sub-monolayer silicon on the oxidation of Al(111) and Al(100) surfaces was investigated using X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. On both surfaces the adatom site is preferred over substituting Si into the Al-lattice; on Al(100) the four fold hollow site is vastly favored whereas on Al(111) bridge and hollow sites are almost equal in energy. Upon O 2 exposure, Si is not oxidized but buried at the metal/oxide interface under the growing aluminum oxide. On Al(111), Si has a catalytic effect on both the initial oxidation by aiding in creating a higher local oxygen coverage in the early stages of oxidation and, in particular, at higher oxide coverages by facilitating lifting Al from the metal into the oxide. The final oxide, as measured from the Al2p intensity, is 25–30% thicker with Si than without. This observation is valid for both 0.1 monolayer (ML) and 0.3 ML Si coverage. On Al(100), on the other hand, at 0.16 ML Si coverage, the initial oxidation is faster than for the bare surface due to Si island edges being active in the oxide growth. At 0.5 ML Si coverage the oxidation is slower, as the islands coalesce and he amount of edges reduces. Upon oxide formation the effect of Si vanishes as it is overgrown by Al 2 O 3 , and the oxide thickness is only 6% higher than on bare Al(100), for both Si coverages studied. Our findings indicate that, in addition to a vanishing oxygen adsorption energy and Mott potential, a detailed picture of atom exchange and transport at the metal/oxide interface has to be taken into account to explain the limiting oxide thickness.

  • 3.
    Korzhavyi, Pavel A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Yunguo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Soroka, I. L.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Exploring configurational degrees of freedom in disordered solids2018In: International Conference of Computational Methods in Sciences and Engineering 2018 (ICCMSE 2018), American Institute of Physics (AIP), 2018, Vol. 2040, article id 020003Conference paper (Refereed)
    Abstract [en]

    Recent computational modeling studies of configurational degrees of freedom in oxide-hydroxides of aluminum and copper are reviewed. Density functional theory calculations are employed to investigate the effect of hydrogen on the structural stability of gamma-alumina and to explore the configurational space of cuprous hydroxide CuOH. Free energy modeling, taking into account configurational and vibrational degrees of freedom, shows that the studied hydrogenated oxides of aluminum and copper are metastable compounds, whereas the respective oxides are thermodynamically stable phases. Selected structural and optical properties of the studied compounds, evaluated using a hybrid functional approach, are reported and compared with available experimental data.

  • 4.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lousada, Claudio Miguel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    The nature of hydrogen in gamma-alumina2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 20, p. 203514-Article in journal (Refereed)
    Abstract [en]

    Gibbs free energy models are derived from the calculated electronic and phonon structure of two possible models of gamma-alumina, a defective spinel phase and a hydrogenated spinel phase. The intrinsic vacancies and hydrogen in the two structural models give rise to a considerable configurational (residual) entropy and significantly contribute to thermodynamic stability and physical-chemical properties of gamma-alumina, which was neglected in previous studies but considered in this work. The electronic densities of states, calculated using a hybrid functional for the two structural models of gamma-alumina, are presented. The dynamic stability of the two phases is confirmed by full-spectrum phonon calculations. The two phases share many similarities in their electronic structure, but can be distinguished by their vibrational spectra and specific heat. The defective spinel is found to be the ground state of gamma-alumina, while the hydrogenated spinel to be a metastable phase. However, dehydration of the metastable phase into the ground state is expected to be slow due to the low diffusion rate of H, which leaves hydrogen as a locked-in impurity in gamma-alumina.

  • 5.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lousada, Claudio Miguel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bond Network Topology and Antiferroelectric Order in Cuprice CuOH2015In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, no 18, p. 8969-8977Article in journal (Refereed)
    Abstract [en]

    Using density functional theory (DFT) and a graph theory based approach, we investigated the topology of bond network in CuOH(s) (cuprice) considering only symmetry-distinct structures. In parallel, we conducted the synthesis and X-ray diffraction characterization of the compound and used the combined theoretical-experimental effort to validate the lowest energy structure obtained with DFT. The ground-state structure of CuOH(s) consists of compact trilayers of CuOH connected to each other via hydrogen bonds, where the inner layer of each trilayer is composed entirely of Cu atoms. Each trilayer is a dense fabric made of two interlocked arrays of polymer [CuOH]<inf>n</inf> chains. This structure corresponds to an antiferroelectric configuration where the dipole moments of CuOH molecules belonging to adjacent arrays are antiparallel and are arranged in the same way as the water molecules in ice-VIII. It is shown that a collective electrostatic interaction is the main driving force for the cation ordering while the local atomic configuration is maintained. These findings and the possibility of synthesizing exfoliated two-dimensional cuprice are important for some technological applications.

  • 6.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Lousada, Cláudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Bonding Topology and Antiferroelectric Order in Cuprice, CuOHManuscript (preprint) (Other academic)
  • 7.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Lousada, Cláudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Cation Ordering in Cuprice, CuOH2015In: Proceedings of PTM 2015, 2015Conference paper (Other academic)
  • 8.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Lousada, Patricio Claudio Miguel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Korzhavy, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Electronic structures and optical properties of cuprous oxide and hydroxide2014In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 1675, p. 185-190Article in journal (Refereed)
    Abstract [en]

    The broad range of applications of copper, including areas such as electronics, fuel cells, and spent nuclear fuel disposal, require accurate description of the physical and chemical properties of copper compounds. Within some of these applications, cuprous hydroxide is a compound whose relevance has been recently discovered. Its existence in the solid-state form was recently reported. Experimental determination of its physical-chemical properties is challenging due to its instability and poop crystallinity. Within the framework of density functional theory calculations (DFT), we investigated the nature of bonding, electronic spectra, and optical properties of the cuprous oxide and cuprous hydroxide. It is found that the hybrid functional PBEO can accurately describe the electronic structure and optical properties of these two copper(I) compounds. The calculated properties of cuprous oxide are in good agreement with the experimental data and other theoretical results. The structure of cuprous hydroxide can be deduced from that of cuprous oxide by substituting half Cu∗ in Cu2O lattice with protons. Compared to CU2O, the presence of hydrogen in CuOH has little effect on the ionic nature of Cu-O bonding, but lowers the energy levels of the occupied states. Thus, CuOH is calculated to have a wider indirect band gap of 2.73 eV compared with the Cu2O band gap of 2.17 eV.

  • 9.
    Lousada, Claudio M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Application of reactivity descriptors to the catalytic decomposition of hydrogen peroxide at oxide surfaces2015In: Computational and Theoretical Chemistry, ISSN 2210-271X, E-ISSN 2210-2728, Vol. 1070, p. 108-116Article in journal (Refereed)
    Abstract [en]

    We have employed density functional theory (DFT) calculations using the PBE0 functional to study the reaction of decomposition of H2O2 on clusters of: ZrO2, TiO2, Y2O3, Fe2O3, CeO2, CuO, Al2O3, NiO2, PdO2 and Gd2O3. The formation of the products of decomposition of H2O2 and their binding onto these oxides are discussed. The obtained energy barriers for H2O2 decomposition deviate from experimental data in absolute average by 4 kJ mol(-1). The only exceptions are CeO2 and Fe2O3 for which the deviations are very large. The adsorption of HO radicals onto the clusters was also studied. Reactivity descriptors obtained with DFT calculations are correlated with experimental data from literature. We found a direct correlation between the adsorption energy of HO radicals and the change in Mulliken charge of the cation present in the oxide, upon adsorption of these radicals. Other DFT and experimentally obtained reactivity descriptors based on properties of the cations present in the oxides, such as the ionization potential and electronegativity are plotted against experimental and DFT computed properties, respectively. Following the Bronsted-Evans Polanyi principle, there is a correlation between the adsorption energy of the product HO radical and the energy barrier for decomposition of H2O2. The good correlations between experimental data and the data obtained with DFF using minimalistic cluster models of the oxides surfaces indicates that on the real systems the processes that determine the reactivity of H2O2 are very dependent on localized properties of the surfaces.

  • 10.
    Lousada, Claudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, A. J.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Adsorption of Hydrogen Sulfide, Hydrosulfide and Sulfide at Cu(110) - Polarizability and Cooperativity Effects. First Stages of Formation of a Sulfide Layer2018In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 17, p. 2159-2168Article in journal (Refereed)
    Abstract [en]

    Understanding the surface site preference for single adsorbates, the interactions between adsorbates, how these interactions affect surface site specificity in adsorption and perturb the electronic states of surfaces is important for rationalizing the structure of interfaces and the growth of surface products. Herein, using density functional theory (DFT) calculations, we investigated the adsorption of H2S, HS and, S onto Cu(110). The surface site specificity observed for single adsorbates can be largely affected by the presence of other adsorbates, especially S that can affect the adsorption of other species even at distances of 13 Å. The large supercell employed with a surface periodicity of (6×6) allowed us to safely use the Helmholtz method for the determination of the dipole of the surface-adsorbate complex at low adsorbate coverages. We found that the surface perturbation induced by S can be explained by the charge transfer model, H2S leads to a perturbation of the surface that arises mostly from Pauli exclusion effects, whereas HS shows a mix of charge transfer and Pauli exclusion effects. These effects have a large contribution to the long range adsorbate-adsorbate interactions observed. Further support for the long range adsorbate-adsorbate interactions are the values of the adsorption energies of adsorbate pairs that are larger than the sum of the adsorption energies of the single adsorbates that constitute the pair. This happens even for large distances and thus goes beyond the H-bond contribution for the H-bond capable adsorbate pairs. Exploiting this knowledge we investigated two models for describing the first stages of growth of a layer of S-atoms at the surface: the formation of islands versus the formation of more homogeneous surface distributions of S-atoms. We found that for coverages lower than 0.5 ML the S-atoms prefer to cluster as islands that evolve to stripes along the [1 (Formula presented.) 0] direction with increasing coverage. At 0.5 ML a homogeneous distribution of S-atoms becomes more stable than the formation of stripes. For the coverage equivalent to 1 ML, the formation of two half-monolayers of S-atoms that disrupt the Cu−Cu bonds between the first and second layer is more favorable than the formation of 1 ML homogeneous coverage of S-atoms. Here the S−Cu bond distances and geometries are reminiscent of pyrite, covellite, and to some extent chalcocite. The small energy difference of ≈0.1 eV that exists between this structure and the formation of 1 ML suggests that in a real system at finite temperature both structures may coexist leading to a structure with even lower symmetry.

  • 11.
    Lousada, Claudio M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Johansson, Adam Johannes
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 17, p. 9533-9543Article in journal (Refereed)
    Abstract [en]

    We performed an experimental and density functional theory (DFT) investigation of the reactions of H2O2 with ZrO2, TiO2, and Y2O3. 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 H2O2 on the surfaces of nano- and micrometersized particles of the oxides. The experimentally obtained enthalpies of activation for the decomposition of H2O2 catalyzed by these materials are 30 +/- 1 kJ.mol(-1) for ZrO2, 34 +/- 1 kJ.mol(-1) for TiO2, and 44 +/- 5 kJ.mol(-1) for Y2O3. 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 H2O2. We compared the performance of the B3LYP and M06 functionals for describing the adsorption energies of H2O2 and HO center dot onto the oxide surfaces as well as the energy barriers for the decomposition of H2O2. The DFT models implemented can describe the experimental reaction barriers with good accuracy, and we found that the decomposition of H2O2 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 H2O2 decomposition, the HO radical, were also addressed both experimentally and with DFT. With the experiments we found a trend in the affinity of HO center dot 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 center dot varies inversely with the ionization energy of the metal cation present in the oxide.

  • 12.
    Lousada, Claudio M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Kinetics, Mechanism, and Activation Energy of H2O2 Decomposition on the Surface of ZrO22010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 25, p. 11202-11208Article in journal (Refereed)
    Abstract [en]

    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) x 10(-5) s(-1) and k(2) = (2.39 +/- 0.09) x 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.ma(-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.

  • 13.
    Lousada, Claudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    First stages of oxide growth on Al(1 1 0) and core-level shifts from density functional theory calculations2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 441, p. 174-186Article in journal (Refereed)
    Abstract [en]

    The formation of islands of O-atoms is the dominant mode of growth of the oxide in the first stages of oxidation of Al(1 1 1). It is however unknown if a similar mechanism exists for other low index surfaces of Al. We performed a density functional theory (DFT) and ab initio molecular dynamics investigation of the first stages of the oxidation of Al(1 1 0) using two distinct models: a homogeneous surface disposition of O-atoms; and a model where the O-atoms are close-spaced forming clusters or islands. We investigated the surface reactions with oxygen up to a coverage of 2 ML and found that for both models the adsorption energy per dissociating O2(g) becomes more negative with increasing coverage. Our results show that for coverages up to 1.25 ML the oxide forms clusters or islands while for coverages higher than 1.5 ML the oxide covers the surface homogeneously. This is because the O-atoms bind preferably to neighboring sites even at the minimum coverage. With increasing coverage, the clusters of O start to form stripes along the [1 1¯ 0] direction. The work function (ϕ) of the surface decreases when going from bare Al(1 1 0) to up to 1 ML coverage of O-atoms, but for coverages of 1.25 ML and higher, ϕ increases. The Al 2p surface core level shifts (SCLS) shift towards higher binding energies with increasing surface coverage of O-atoms and start to approach the values of Al 2p in Al2O3 already at a coverage of 2ML. A relation between the SCLS and the coordination number of Al to O-atoms was made. The Al 2p SCLS increases with increasing coordination to O-atoms, for single, twofold and three-fourfold coordinated cations. For the O-atoms that terminate the surface at the short-bridge sites, the SCLS of O 1s, is largely affected by the proximity to other O-atoms. These results demonstrate that the cooperative effects between surface bound O-atoms have important roles in the mechanism of growth of the oxide at Al(1 1 0), and similarly to what happens for Al(1 1 1), the initial oxidation of Al(1 1 0) proceeds via the formation of islands of O-atoms.

  • 14.
    Lousada, Claudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. RAS, Ural Div, Inst Met Phys, Ekaterinburg 620219, Russia..
    The first stages of oxide growth at the low index Al surfaces (100), (110), (111): clusters and stripes vs. homogeneous growth2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 46, p. 29549-29557Article in journal (Refereed)
    Abstract [en]

    We performed a density functional theory (DFT) investigation of the mechanisms of oxide growth at Al(100), Al(110) and Al(111) up to 1 monolayer (ML) coverage of O-atoms with 0.125 ML increments. We found that the surface binding site preferences of O-atoms are largely affected by the presence of neighboring O-atoms. Based on this we constructed two oxide growth models: the formation of clusters that evolve to stripes with increasing coverage and the formation of a more homogeneous distribution of O-atoms. While the former model is characterized by a lower symmetry of distribution of O-atoms at the surfaces, the latter corresponds to higher symmetries. We found that the prevalence of each oxide growth mode depends on the coverage of O-atoms and that this dependency is different for each surface. For Al(100) and Al(110), up to coverages of 1 ML the oxide grows preferably via the formation of clusters that evolve to stripes with increasing coverage, while for Al(111) the stripes and clusters are the preferred growth mode for coverages up to 0.375 ML, beyond which the homogeneous growth mode is energetically favored. The calculated Al-O pair distribution functions show that the formation of clusters and stripes leads to shorter Al-O bond lengths when compared to the homogeneous growth. The oxides formed at Al(100) and Al(110) have Al-O bond lengths and geometries typical of the shorter bonds of -alumina while at Al(111) the bond lengths are typical of -alumina and -alumina. These results suggest that for low coverages, the oxides formed at Al(100) and Al(110) are resemblant of defective -alumina while the oxide formed at Al(111) is similar to less disordered -alumina and -alumina. For Al(111), the small energy difference between the growth of clusters and stripes and homogeneous growth does not exclude the coexistence of both growth modes; this could lead to the formation of a defective or amorphous oxide.

  • 15.
    Lousada, Claudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Oxygen adsorption onto pure and doped Al surfaces - the role of surface dopants2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 3, p. 1667-1679Article in journal (Refereed)
    Abstract [en]

    Using density functional theory (DFT) with the PBE0 density functional we investigated the role of surface dopants in the molecular and dissociative adsorption of O-2 onto Al clusters of types Al-50, Al50Alad, Al50X and Al49X, where X represents a dopant atom of the following elements Si, Mg, Cu, Sc, Zr, and Ti. Each dopant atom was placed on the Al(111) surface as an adatom or as a substitutional atom, in the last case replacing a surface Al atom. We found that for the same dopant geometry, the closer is the ionization energy of the dopant element to that of elemental Al, the more exothermic is the dissociative adsorption of O-2 and the stronger are the bonds between the resulting O atoms and the surface. Additionally we show that the Mulliken concept of electronegativity can be applied in the prediction of the dissociative adsorption energy of O-2 on the doped surfaces. The Mulliken modified second-stage electronegativity of the dopant atom is proportional to the exothermicity of the dissociative adsorption of O-2. For the same dopant element in an adatom position the dissociation of O-2 is more exothermic when compared to the case where the dopant occupies a substitutional position. These observations are discussed in view of the overlap population densities of states (OPDOS) computed as the overlap between the electronic states of the adsorbate O atoms and the clusters. It is shown that a more covalent character in the bonding between the Al surface and the dopant atom causes a more exothermic dissociation of O-2 and stronger bonding with the O atoms when compared to a more ionic character in the bonding between the dopant and the Al surface. The extent of the adsorption site reconstruction is dopant atom dependent and is an important parameter for determining the mode of adsorption, adsorption energy and electronic structure of the product of O-2 adsorption. The PBE0 functional could predict the existence of the O-2 molecular adsorption product for many of the cases investigated here.

  • 16.
    Lousada, Claudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Surface Chemistry of Oxygen on Aluminum-Performance of the Density Functionals: PBE, PBE0, M06, and M06-L2016In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 37, no 9, p. 787-794Article in journal (Refereed)
    Abstract [en]

    We investigated the performance of the density functional theory (DFT) functionals PBE, PBE0, M06, and M06-L for describing the molecular and dissociative adsorption of O2 onto pure and doped Al(111) surfaces. Adsorption of O2 was studied at the perfect Al(111) surface and compared with the case where an additional Al atom was present as an adatom. Additionally, we studied how these functionals perform when different dopants are present at the Al(111) surface in two distinct geometries: as an adatom or as a substitutional atom replacing an Al atom. The performance of the different functionals is greatly affected by the surface geometry. The inclusion of Hartree-Fock exchange in the functional leads to slight differences in adsorption energies for molecular adsorption of O2. These differences become very pronounced for dissociative adsorption, with the hybrids PBE0 and M06 predicting more exergonic adsorption than PBE and M06-L. Furthermore, PBE0 and M06 predicted trends in adsorption energies for defective and perfect surfaces which are in line with the experimental knowledge of the effects of surface defects in adsorption energies. The predictions of the non-hybrids PBE and M06-L point in the opposite direction. The analysis of the contributions of the van der Waals (vdW) forces to the adsorption energies reveals that the PBE and PBE0 functionals have similar difficulties in describing vdW interactions for molecular adsorption of O2 while the M06 functional can give a description of these forces with an accuracy which is at least similar to that of the correction of the D3 type.

  • 17.
    Lousada, Claudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Sophonrat, Nanta
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Weihong, Yang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mechanisms of Formation of H, HO, and Water and of Water Desorption in the Early Stages of Cellulose Pyrolysis2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 23, p. 12168-12176Article in journal (Refereed)
    Abstract [en]

    Here, we report the results from a combined first-principles and experimental investigation of the initial stages of decomposition of cellulose during heating in pyrolysis. Density functional theory calculations with periodic boundary conditions were performed to investigate the formation of H and HO radicals and of the molecular products H2O, H-2, and H2O2 originating from their recombination. The stabilization that alcohol groups impart to adjacent C-radicals and the allylic recombination of unpaired electrons of neighboring C-radicals play decisive roles in the decomposition mechanism. This makes the simultaneous formation of H-center dot from C2 and HO center dot from C3 the most favorable process. The recombination of these radicals to form water leads to an additional stabilization of the reaction. The computed temperature-dependent reactions Gibbs' free energies reveal that desorption of H2O from intact cellulose occurs at T = 147 degrees C and that gas-phase water forms spontaneously from the decomposition of cellulose at T = 282 degrees C. These results are in excellent agreement with our experimental study of the pyrolysis done with pyrolysis gas chromatography/mass spectrometry at different temperatures. The experiments show that upon heating, a small amount of water is released from cellulose at 210 degrees C, and a considerably larger amount starts to be released at 280 degrees C.

  • 18.
    Lousada, Claudio Miguel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Johansson, Adam Johannes
    Korzhavyi, Pavel A
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Thermodynamics of H2O Splitting and H-2 Formation at the Cu(110)-Water Interface2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 25, p. 14102-14113Article in journal (Refereed)
    Abstract [en]

    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 molecules. According to the obtained Gibbs free energies, the formation of half a inonolayer of HO and the corresponding amount of hydrogen gas is spontaneous (Delta(r)G(0) < 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 nonspontaneous (Delta(r)G(o) > 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 H2O takes place. We found that even though the Gibbs free energy changes associated with the first steps of dehydrogenation of H2O 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 H2O 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.

  • 19.
    Lousada, Claudio Miguel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    LaVerne, Jay A.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Enhanced hydrogen formation during the catalytic decomposition of H2O2 on metal oxide surfaces in the presence of HO radical scavengers2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 30, p. 12674-12679Article in journal (Refereed)
    Abstract [en]

    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 center dot by means of Tris or TAPS buffer leads to enhanced formation of H-2. In parallel, a decrease in the production of the main gaseous product O-2 is observed. Under these conditions, H-2 formation is a spontaneous process even at room temperature. The yields of both the H-2 and O-2 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 O-2 and H-2 are formed at different types of surface sites.

  • 20.
    Lousada, Claudio Miguel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Yagodzinskyy, Y.
    Tarakina, N. V.
    Todoshchenko, O.
    Hänninen, H.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Gamma radiation induces hydrogen absorption by copper in water2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 24234Article in journal (Refereed)
    Abstract [en]

    One of the most intricate issues of nuclear power is the long-term safety of repositories for radioactive waste. These repositories can have an impact on future generations for a period of time orders of magnitude longer than any known civilization. Several countries have considered copper as an outer corrosion barrier for canisters containing spent nuclear fuel. Among the many processes that must be considered in the safety assessments, radiation induced processes constitute a key-component. Here we show that copper metal immersed in water uptakes considerable amounts of hydrogen when exposed to γ-radiation. Additionally we show that the amount of hydrogen absorbed by copper depends on the total dose of radiation. At a dose of 69 kGy the uptake of hydrogen by metallic copper is 7 orders of magnitude higher than when the absorption is driven by H2(g) at a pressure of 1 atm in a non-irradiated dry system. Moreover, irradiation of copper in water causes corrosion of the metal and the formation of a variety of surface cavities, nanoparticle deposits, and islands of needle-shaped crystals. Hence, radiation enhanced uptake of hydrogen by spent nuclear fuel encapsulating materials should be taken into account in the safety assessments of nuclear waste repositories.

  • 21.
    Lousada, Claudio Miguel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Yang, Miao
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Nilsson, Kristina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides2013In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 379, p. 178-184Article in journal (Refereed)
    Abstract [en]

    We have investigated the reactions of H2O2 with Fe2O3, CuO, HfO2, CeO2 and Gd 2O3 in aqueous solution. The reactions rate constants at room temperature were determined. From the temperature dependence of the rate constants we extracted the Arrhenius parameters and the standard enthalpies of activation for the reactions. In addition, we studied the dynamics of formation of the intermediate species formed during decomposition of H2O 2, the HO radical. The kinetic data for H2O2 reactivity and the yields of hydroxyl radical formation differ considerably between many of the materials studied. We compared the energetic and mechanistic data obtained in this work with literature data for a set of nine oxides in total. The Arrhenius pre-exponential factors normalized to surface area for the decomposition of H2O2 vary by nine orders of magnitude for some of the oxides investigated. This indicates that the surfaces of the oxides have very different catalytic capacity towards the decomposition of H 2O2. The standard enthalpies of activation for H 2O2 decomposition vary between 30 and 73 kJ mol -1, revealing also differences in the catalytic efficiency for the different materials. The mechanistic study consists of quantifying the HO radical scavenged by tris(hydroxymethyl)aminomethane (Tris) during the course of the decomposition of H2O2 for the whole set of oxides. The yields and dynamics of scavenging of HO• differ considerably between the oxides analyzed. Surprisingly, the time-independent plots of the amount of HO scavenged as a function of the conversion of H2O 2 reveals that during the decomposition of H2O2 there are turnover points where the amount of HO scavenged by Tris suffers a sudden increase. The location of these points and the curvatures of the plots at the near-neighbours is considerably different for the different materials.

  • 22.
    Lousada, Cláudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Fernandes, Ricardo M. F.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Tarakina, Nadezda V.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Synthesis of copper hydride (CuH) from CuCO3·Cu(OH)2 – a path to electrically conductive thin films of Cu2017In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 20, p. 6533-6543Article in journal (Refereed)
    Abstract [en]

    The most common synthesis methods for copper hydride (CuH) employ hard ligands that lead to the formation of considerable amounts of metallic Cu as side-product. Here we explore a synthesis method for CuH(s) through the reaction of CuCO3 center dot Cu(OH)(2)(s) with hypophosphorous acid (H3PO2) in solution, via the formation of the intermediate Cu(H2PO2)(2)(aq) complex. The reaction products were characterized with XRD, FTIR and SEM at different reaction times, and the kinetics of the transformation of Cu(H2PO2)(2)(aq) to CuH(s) were followed with NMR and are discussed. We show that our synthesis method provides a simple way for obtaining large amounts of CuH(s) even when the synthesis is performed in air. Compared to the classic Wurtz method, where CuSO4 is used as an initial source of Cu2+, our synthesis produces CuH particles with less metallic Cu side-product. We attribute this to the fact that our reaction medium is free from the hard SO42- ligand that can disproportionate Cu(I). We discuss a mechanism for the reaction based on the known reactivity of the reagents and intermediates involved. We explored the possibility of using CuH(s) for making electrically conductive films. Tests that employed water-dispersed CuH particles show that this compound can be reduced with H3PO2 leading to electrically conductive thin films of Cu. These films were made on regular office paper and were found to be Ohmic conductors even after several weeks of exposure to ambient conditions. The fact that the synthesis reported here produces large amounts of CuH particles in aqueous media, with very little impurities, and the fact that these can then be converted to a stable electrically conductive film can open up new applications for CuH such as for printing electrically conductive films or manufacturing surface coatings.

  • 23.
    Lousada, Cláudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Johansson, Adam Johannes
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Molecular and dissociative adsorption of water and hydrogen sulfide at perfect and defective Cu(110) surfaces2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, p. 8111-8120Article in journal (Refereed)
    Abstract [en]

    We performed a density functional theory (DFT) investigation of the molecular and dissociative adsorption of H2O and H2S at perfect and defective Cu(110) surfaces described using supercells with c(6 × 6) periodicity. The defective surface consists of a terrace surrounded by pits. We found considerable differences in adsorption modes and energies for H2O and H2S. At the defective Cu(110) surface, monomers of H2O and H2S preferentially adsorb at the terrace site and molecular adsorption of H2O is significantly more favorable than that of H2S. For dissociative adsorption however, the sulfur species are considerably more stable than the oxygen species. For monolayer (ML) coverages, there are small differences in the molecular adsorption energies for H2O and H2S. However, for the formation of 1 ML of HO and 1 ML of HS from 1 ML of H2O and 1 ML of H2S, respectively, with the release of H2(g), the differences are very large. The formation of 1 ML HO at the perfect Cu(110) surface is endoergic, while at the defective Cu(110) surface it is exoergic by −0.6 eV. For high coverages, H2S forms stacked half-monolayers that interact with each other via a complex hydrogen bond network with a strength per H2S molecule of −0.140 eV per H2S and −0.120 eV per H2S for H2S located in the underlayer and overlayer, respectively. The large distances between hydrogen bonded H2S molecules explain the preference for the formation of the two stacked half-monolayers of H2S instead of a single monolayer as it happens with H2O. Additionally, the formation of 1 ML of HS does not occur because of the spontaneous splitting of some H–S bonds resulting in surface bound HS and S and H2S molecules. Extensive surface reconstruction and relaxation accompanies adsorption of the sulfur adsorbates. Such reconstructions with outwards pull of Cu atoms can be at the origin of the weak adhesion of sulfide films that explains the release of CuS particles from copper sulfide films at copper surfaces. Overall, the surface defects here investigated induce non-linear effects in the molecular and dissociative adsorption energies of different O and S adsorbates.

  • 24.
    Lousada, Cláudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Johansson, Adam Johannes
    Korzhavyi, Pavel A.
    Molecular and dissociative adsorption of water at a defective Cu(110) surface2017In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 658, p. 1-8Article in journal (Refereed)
    Abstract [en]

    We performed a density functional theory (DFT) investigation of the molecular and dissociative adsorption of water at the perfect Cu(110) and at a defective Cu surface that provides a broad spectrum of adsorption sites in terms of coordination of Cu atoms, with the aim of understanding the role of surface defects in the dissociation of water molecules. The molecular adsorption of water is spontaneous at both surfaces but at the defective surface we found two stable molecular adsorption structures that differ slightly in the disposition of the O-atoms of H2O on the surface plane but differ considerably on the orientation of their H-atoms. Additionally we studied the dissociative adsorption of water accompanied with formation of H2(g). At the defective surface, starting from 1 ML of molecularly adsorbed H2O, the dissociation of 0.22 ML of H2O leading to 0.22 ML of HO, 0.78 ML H2O and H2(g) is exergonic but the dissociation of 0.44 ML or more H2O molecules is endergonic. These findings are discussed in terms of the two main factors that affect the adsorption energies: the existence of exposed adatoms provides an environment that facilitates the interaction with small adsorbates leading to stronger bonds between the surface and such adsorbates; and at the same time, the limited polarizability of the defect sites causes high coverages of adsorbates that drag electron density from the surface to be unfavorable. The overall effect is that at the defective Cu(110) formation of low coverages of HO groups is more favorable than at the perfect Cu(110) while forming coverages higher than 0.44 ML of HO is less favorable than at the perfect Cu(110). These effects have their origin in the extent of the polarization of the Cu–O bonds.

  • 25.
    Lousada, Cláudio M.
    et al.
    Universidade de Lisboa, Lisboa, Portugal.
    Pinto, Susana S.
    Instituto Superior Tecnico da Universidade Tecnica de Lisboa, Lisboa, Portugal.
    Canongia Lopes, José N.
    Instituto Superior Tecnico da Universidade Tecnica de Lisboa, Lisboa, Portugal.
    Minas da Piedade, M. Fátima
    Universidade de Lisboa, Lisboa, Portugal.
    Diogo, Hermínio P.
    Instituto Superior Tecnico da Universidade Tecnica de Lisboa, Lisboa, Portugal.
    Minas da Piedade, Manuel E.
    Universidade de Lisboa, Lisboa, Portugal.
    Experimental and Molecular Dynamics Simulation Study of the Sublimation and Vaporization Energetics of Iron Metalocenes. Crystal Structures of Fe(η5-C5H4CH3)2 andFe[(η5-(C5H5)(η5-C5H4CHO)]2008In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, p. 2977-2987Article in journal (Refereed)
    Abstract [en]

    The standard molar enthalpies of sublimation of ferrocene, 1,1'-dimethylferrocene, decamethylferrocene, ferrocenecarboxaldehyde and R-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 ΔsubH°m and ΔvapH°m 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 ΔsubH°m 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(η5-C5H4CH3)2 and Fe[(η5-(C5H5)(η5-C5H4CHO)] at 293 and 150 K, respectively, are reported.

  • 26.
    Lousada, Cláudio M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Trummer, Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Reactivity of H2O2 towards different UO2-based materials: The relative impact of radiolysis products revisited2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 434, no 1/3, p. 434-439Article in journal (Refereed)
    Abstract [en]

    The reactivity of doped UO2 such as SIMFUEL towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. In this work we have studied the mechanistic difference between SIMFUEL and pure UO2. H2O2 can be catalytically decomposed on UO2 in competition with the redox process in which U(IV) is oxidized. The latter process leads to the dissolution of oxidized uranium. The first step in the catalytic decomposition is the formation of hydroxyl radicals. The presence of hydroxyl radicals was verified using Tris buffer as a radical scavenger. For both UO2 and SIMFUEL pellets, significant amounts of hydroxyl radicals were formed. The results also show that the difference in dissolution yield between the two materials can mainly be attributed to differences in the redox reactivity. Based on this, the rate constants for electron transfer were revised and the relative impact of the radiolytic oxidants in oxidative dissolution of UO2 and SIMFUEL pellets were calculated. The impact of H2O2 is shown to be slightly reduced.

  • 27.
    Lousada Patricio, Cláudio Miguel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Johansson, Adam Johannes
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Reactivity of metal oxide clusters with hydrogen peroxide and water: a DFT study evaluating the performance of different exchange-correlation functionals2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 15, p. 5539-5552Article in journal (Refereed)
    Abstract [en]

    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.

  • 28.
    Lousada Patrício, Cláudio Miguel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Reactions of aqueous radiolysis products with oxide surfaces: An experimental and DFT study2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The reactions between aqueous radiolysis products and oxide surfaces are important in nuclear technology in many ways. In solid-liquid systems, they affect (and at the same time are dependent on) both the solution chemistry and the stability of materials under the influence of ionizing radiation. The stability of surface oxides is a factor that determines the longevity of the materials where such oxides are formed. Additionally, the aqueous radiolysis products are responsible for corrosion and erosion of the materials.

      In this study, the reactions between radiolysis products of water – mainly H2O2 and HO radicals – with metal, lanthanide and actinide oxides are investigated. For this, experimental and computational chemistry methods are employed. For the experimental study of these systems it was necessary to implement new methodologies especially for the study of the reactive species – the HO radicals. Similarly, the computational study also required the development of models and benchmarking of methods. The experiments combined with the computational chemistry studies produced valuable kinetic, energetic and mechanistic data.

      It is demonstrated here that the HO radicals are a primary product of the decomposition of H2O2. For all the materials, the catalytic decomposition of H2O2 consists first of molecular adsorption onto the surfaces of the oxides. This step is followed by the cleavage of the O-O bond in H2O2 to form HO radicals. The HO radicals are able to react further with the hydroxylated surfaces of the oxides to form water and a surface bound HO center. The dynamics of formation of HO vary widely for the different materials studied. These differences are also observed in the activation energies and kinetics for decomposition of H2O2. It is found further that the removal of HO from the system where H2O2 undergoes decomposition, by means of a scavenger, leads to the spontaneous formation of H2.

      The combined theoretical-experimental methodology led to mechanistic understanding of the reactivity of the oxide materials towards H2O2 and HO radicals. This reactivity can be expressed in terms of fundamental properties of the cations present in the oxides. Correlations were found between several properties of the metal cations present in the oxides and adsorption energies of H2O, adsorption energies of HO radicals and energy barriers for H2O2 decomposition. This knowledge can aid in improving materials and processes important for nuclear technological systems, catalysis, and energy storage, and also help to better understand geochemical processes.

  • 29. Masood Hafez Haghighat, Seyed
    et al.
    Martin-Bragado, Ignacio
    Lousada, Cláudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Korzhavyi, Pavel A.
    Discrete Models: Down to Atoms and Electrons2016In: Handbook of Software Solutions for ICME, Weinheim, Germany: Wiley-VCH Verlagsgesellschaft, 2016, p. 385-431Chapter in book (Other academic)
    Abstract [en]

    This chapter reviews some computational methods and software tools available for modeling materials at small scales where the matter exhibits its discrete nature. Discrete models operate on different levels, ranging from the electronic structure and atomistic level to the mesoscopic level at which the discrete objects are molecules or crystal defects rather than the individual atoms. The chapter considers the main methods of atomistic modeling, molecular dynamics (MD) and Monte Carlo (MC), and quantum mechanics (QM) electronic structure methods. It discusses the effective potentials, interatomic interactions, and force fields (FFs), which serve the purpose of passing the physical information between the different levels of modeling. Two atomistic methods are also reviewed. Kinetic MC (KMC) is first introduced as a technique able to link the nanoscale and mesoscale domains but relying heavily on atomistic parameterizations. Then, the powerful MD technique is explained, and some links between both techniques are also hinted.

  • 30. Pehrman, Reijo
    et al.
    Trummer, Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lousada, Claudio Miguel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    On the redox reactivity of doped UO2 pellets - Influence of dopants on the H2O2 decomposition mechanism2012In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 430, no 1-3, p. 6-11Article in journal (Refereed)
    Abstract [en]

    The reactivity of doped UO2 such as SIMFUEL, Y2O3 doped UO2 and Y2O3/Pd doped UO2 towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. The rationale for the observed differences in dissolution yield is a difference in the ratio between the rates of the two possible reactions between H2O2 and the doped UO2. In this work we have studied the effect of doping on the two possible reactions, electron-transfer and catalytic decomposition. The catalytic decomposition was studied by monitoring the hydroxyl radical production (the primary product) as a function of time. The redox reactivity of the doped pellets was studied by using MnO4- and IrCl62- as model oxidants, only capable of electron-transfer reactions with the pellets. In addition, the activation energies for oxidation of UO2 and SIMFUEL by MnO4- were determined experimentally. The experiments show that the rate of catalytic decomposition of H2O2 varies by 30% between the most and least reactive material. This is a negligible difference compared to the difference in oxidative dissolution yield. The redox reactivity study shows that doping UO2 influences the redox reactivity of the pellet. This is further illustrated by the observed activation energy difference for oxidation of UO2 and SIMFUEL by MnO4-. The redox reactivity study also shows that the sensitivity to dopants increases with decreasing reduction potential of the oxidant. These findings imply that the relative impact of radiolytic oxidants in oxidative dissolution of spent nuclear fuel must be reassessed taking the actual fuel composition into account.

  • 31.
    Pehrman, Reijo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Trummer, Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Lousada, Cláudio
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    On the redox reactivity of doped UO2 pellets: Influence of dopants on the H2O2 decomposition mechanism.Manuscript (preprint) (Other academic)
    Abstract [en]

    The reactivity of doped UO2 such as SIMFUEL, Y2O3 doped UO2 and Y2O3/Pd doped UO2 towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. The rationale for the observed differences in dissolution yield is a difference in the ratio between the rates of the two possible reactions between H2O2 and the doped UO2. In this work we have studied the effect of doping on the two possible reactions, electron transfer and catalytic decomposition. The catalytic decomposition was studied by monitoring the hydroxyl radical production (the primary product) as a function of time. The redox reactivity of the doped pellets was studied by using MnO4- and IrCl62- as model oxidants, only capable of electron transfer reaction with the pellets. In addition, the activation energies for oxidation of UO2 and SIMFUEL by MnO4- were determined experimentally. The experiments show that the rate of catalytic decomposition of H2O2 varies by 30 % between the fastest and the slowest material. This is a negligible difference. The redox reactivity study shows that doping of UO2 influences the redox reactivity of the pellet. This is further illustrated by the observed activation energy difference for oxidation of UO2 and SIMFUEL by MnO4-. The redox reactivity study also shows that the sensitivity to dopants increases with decreasing reduction potential of the oxidant. These findings imply that the relative impact of radiolytic oxidants in oxidative dissolution of spent nuclear fuel must be reassessed taking the actual fuel composition into account.

  • 32.
    Sophonrat, Nanta
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Linda
    RISE Energy Technol Ctr AB, Box 726, SE-94128 Pitea, Sweden..
    Svanberg, Rikard
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Han, Tong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dvinskikh, Sergey
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ex Situ Catalytic Pyrolysis of a Mixture of Polyvinyl Chloride and Cellulose Using Calcium Oxide for HCl Adsorption and Catalytic Reforming of the Pyrolysis Products2019In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 58, no 31, p. 13960-13970Article in journal (Refereed)
    Abstract [en]

    In the context of chemical recycling of mixed plastics and paper, multitemperature step pyrolysis has shown good potential for the separation of oxygenated products from hydrocarbons. Here, we report results of an investigation of the first pyrolysis step at low temperature, which involves the dehydrochlorination of polyvinyl chloride (PVC) and the pyrolysis of cellulose, the main component of paper. Calcium oxide (CaO), selected for its chloride adsorption ability and its catalytic activity on biooil deoxygenation, was used for upgrading the downstream products from the pyrolysis. Additionally, we studied the performance of CaO for the simultaneous adsorption of HCl and for reforming cellulose pyrolysates in the temperature range of 300-600 degrees C with feedstock to CaO ratios of 1:0.2, 1:0.4, and 1:1. It was found that the suitable catalytic temperature for HCl and acetic acid adsorption is lower than 400 degrees C. This is due to the desorption of HCl from CaCl2 and Ca(OH)Cl in the presence of water and CO2 at 400 degrees C and higher. A larger amount of CaO resulted in a more efficient reduction of acids and the organic liquids were found to have lower amounts of oxygen. A comparison between the cases of neat and mixed feedstock showed that pyrolysis of mixed feedstock produced more water, H-2, CO, and polycyclic aromatic hydrocarbons (PAHs) when compared to the case of neat materials over CaO.

  • 33.
    Sophonrat, Nanta
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Linda
    RISE ETC.
    Svanberg, Rikard
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Han, Tong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dvinskikh, Sergey
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yang, Weihong
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Ex-situ catalytic pyrolysis of a mixture of PVC and cellulose using calcium oxide for HCl adsorption and catalytic reforming of the pyrolysis productsManuscript (preprint) (Other academic)
    Abstract [en]

    In the context of chemical recycling of mixed plastics and paper, multi-temperature step pyrolysis has shown good potential for the separation of oxygenated products from hydrocarbons. Here, we report results of an investigation of the first pyrolysis step at low temperature, which involves the dehydrochlorination of polyvinyl chloride (PVC) and the pyrolysis of cellulose—the main component of paper. Calcium oxide (CaO), selected for its chloride adsorption ability and its catalytic activity on biooil deoxygenation, was used for upgrading the downstream products from the pyrolysis. Additionally, we studied the performance of CaO for the simultaneous adsorption of HCl and for reforming cellulose pyrolysates in the temperature range of 300-600 °C with feedstock to CaO ratios of 1:0.2, 1:0.4 and 1:1. It was found that the suitable catalytic temperature for HCl and acetic acid adsorption is lower than 400 °C. This is due to the reaction of CaO with water that causes the desorption of HCl at temperatures above 400 °C. A larger amount of CaO resulted in a more efficient reduction of acids and the organic liquids were found to have lower amounts of oxygen. A comparison between the cases of neat and mixed feedstock showed that pyrolysis of mixed feedstock produced more water, H2, CO and polycyclic aromatic hydrocarbons (PAHs) when compared to the case of neat materials over CaO.

  • 34. Xia, S.
    et al.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermo-Calc Software AB, Solna, Sweden.
    Maier, A. C.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, Y.
    Zhang, Y.
    Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys2018In: Frontiers in Materials, ISSN 2296-8016, Vol. 5, article id 53Article in journal (Refereed)
    Abstract [en]

    We performed a combined experimental and theoretical investigation of the oxidation behavior of pure Ni and of the following multi-component Ni-containing alloys with nearly equiatomic compositions: FeNi, CoFeNi, CoCrFeNi, and CoCrFeMnNi. The materials were exposed to air at ambient pressure and at a temperature of 800°C for 150 min, their weight-gain due to oxidation was continuously monitored and the products of oxidation were subsequently characterized by XRD. The most common oxides formed have spinel or halite structure and the materials resistance to oxidation increases as: FeNi &lt; CoFeNi &lt; Ni &lt; CoCrFeMnNi &lt; CoCrFeNi. We found further that the oxidation-resistance of the materials does not correlate linearly with the number of elements present, instead the type of elements impacts significantly the materials susceptibility to oxidative damage. Cr is the element that imparted higher resistance to oxidation while Mn and Fe worsened the materials performance. In order to better understand the mechanisms of oxidation we employed thermodynamic equilibrium calculations and predicted the phase stability of oxides of the elements that are present in the materials, in different ranges of temperature, composition and oxygen activity. Additionally, we determined the phase compositions for the thermodynamically stable oxides at 800°C. The results from the thermodynamic modeling are in good agreement with the experimental finds. The alloys with low resistance to oxidation such as CoFeNi and FeNi, form the Fe 3 O 4 spinel phase which tends to dominate the phase diagram for these materials. The presence of Cr increases the resistance to atomic rearrangement due to slow diffusion in the complex structure of Cr containing spinel phases. This causes the extremely high resistance to oxidation of the CoCrFeNi alloy. The presence of Mn in CoCrFeNi stabilizes the Mn 3 O 4 spinel, which reduces the oxidation-resistance of the alloys due to the high mobility of Mn.

  • 35.
    Xia, Songqin
    et al.
    Univ Sci & Technol Beijing, State Key Lab Adv Met & Mat, Beijing, Peoples R China.;Peking Univ, State Key Lab Nucl Phys & Technol, Beijing, Peoples R China.;KTH Royal Inst Technol, Dept Mat Sci & Engn, Stockholm, Sweden..
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Thermocalc Software AB, Solna, Sweden..
    Maier, Annika C.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, Yugang
    Peking Univ, State Key Lab Nucl Phys & Technol, Beijing, Peoples R China..
    Zhang, Yong
    Univ Sci & Technol Beijing, State Key Lab Adv Met & Mat, Beijing, Peoples R China..
    Nonlinear Oxidation Behavior in Pure Ni and Ni-Containing Entropic Alloys (vol 5, 53, 2018)2018In: FRONTIERS IN MATERIALS, ISSN 2296-8016, Vol. 5, article id 73Article in journal (Refereed)
  • 36. Xia, Songqin
    et al.
    Lousada, Claudio M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Maier, Annika Carolin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sandström, Rolf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, Y.
    Zhang, Y.
    Erratum: Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys (Front. Mater., (2018) 5, 53, 10.3389/fmats.2018.00053)2018In: Frontiers in Materials, ISSN 2296-8016, Vol. 5, article id 73Article in journal (Refereed)
    Abstract [en]

    In the original article, there was an error. An explanation should be inserted at the beginning of the section Thermodynamic Calculations, Paragraph 1, line 1: In this as well as the following paragraphs the authors refer to phases such as halite, spinel, corundum etc. It thereby solely referred to the structure type and not the respective mineral. In the original article, there was an error. The word "sfinancial" should be corrected to "financial" in the Acknowledgements section, Paragraph 1: The Carl Tryggers Stiftelse för Vetenskaplig Forskning is gratefully acknowledged for financial support. The authors apologize for these errors and state that they do not change the scientific conclusions of the article in any way. The original article has been updated.

1 - 36 of 36
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