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Reactions of aqueous radiolysis products with oxide surfaces: An experimental and DFT study
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-0086-5536
2013 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , 121 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:12
Keyword [en]
hydrogen peroxide, hydrogen production, metal, oxides, lanthanide, catalysis, density functional theory, surface, reactions, chemistry
National Category
Physical Chemistry Materials Chemistry Theoretical Chemistry
Research subject
SRA - Energy; SRA - Production
Identifiers
URN: urn:nbn:se:kth:diva-119780ISBN: 978-91-7501-683-2 (print)OAI: oai:DiVA.org:kth-119780DiVA: diva2:612445
Public defence
2013-04-12, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
StandUpXPRES - Initiative for excellence in production research
Note

QC 20130322

Available from: 2013-03-22 Created: 2013-03-21 Last updated: 2013-03-22Bibliographically approved
List of papers
1. Kinetics, Mechanism, and Activation Energy of H2O2 Decomposition on the Surface of ZrO2
Open this publication in new window or tab >>Kinetics, Mechanism, and Activation Energy of H2O2 Decomposition on the Surface of ZrO2
2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 25, 11202-11208 p.Article in journal (Refereed) Published
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.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-27269 (URN)10.1021/jp1028933 (DOI)000278982300028 ()2-s2.0-77954050130 (Scopus ID)
Note
QC 20101216Available from: 2010-12-16 Created: 2010-12-09 Last updated: 2017-12-11Bibliographically approved
2. Reactivity of H2O2 towards different UO2-based materials: The relative impact of radiolysis products revisited
Open this publication in new window or tab >>Reactivity of H2O2 towards different UO2-based materials: The relative impact of radiolysis products revisited
2013 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 434, no 1/3, 434-439 p.Article in journal (Refereed) Published
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.

Keyword
Radiation-Induced Dissolution, Waste-Disposal Conditions, Spent Nuclear-Fuel, Oxidative Dissolution, Uranium-Dioxide, Uo2, Hydrogen, Corrosion, Kinetics, Decomposition
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-32918 (URN)10.1016/j.jnucmat.2011.06.003 (DOI)000315752000056 ()2-s2.0-84882753951 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, FP7-212287
Note

 Updated from manuscript to article in journal. QC 20130322

Available from: 2011-04-27 Created: 2011-04-26 Last updated: 2017-12-11Bibliographically approved
3. On the redox reactivity of doped UO2 pellets - Influence of dopants on the H2O2 decomposition mechanism
Open this publication in new window or tab >>On the redox reactivity of doped UO2 pellets - Influence of dopants on the H2O2 decomposition mechanism
2012 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 430, no 1-3, 6-11 p.Article in journal (Refereed) Published
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.

Keyword
Radiation-Induced Dissolution, Waste-Disposal Conditions, Spent Nuclear-Fuel, Uranium-Dioxide, Oxidative Dissolution, Fission-Products, Aqueous-Solution, Corrosion, Radicals, Kinetics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-109203 (URN)10.1016/j.jnucmat.2012.06.016 (DOI)000310940700002 ()2-s2.0-84864026579 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, FP7-212287
Note

QC 20121221

Available from: 2012-12-21 Created: 2012-12-21 Last updated: 2017-12-06Bibliographically approved
4. Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces
Open this publication in new window or tab >>Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 17, 9533-9543 p.Article in journal (Refereed) Published
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.

Keyword
Activation energy, Adsorption, Density functional theory, Enthalpy, Metallic compounds, Rate constants, Titanium dioxide, Transition metals, Zirconium alloys
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-95488 (URN)10.1021/jp300255h (DOI)000303426500019 ()2-s2.0-84860521785 (Scopus ID)
Note

QC 20120528

Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
5. Reactivity of metal oxide clusters with hydrogen peroxide and water: a DFT study evaluating the performance of different exchange-correlation functionals
Open this publication in new window or tab >>Reactivity of metal oxide clusters with hydrogen peroxide and water: a DFT study evaluating the performance of different exchange-correlation functionals
2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 15, 5539-5552 p.Article in journal (Refereed) Published
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.

Keyword
Generalized Gradient Approximation, Temperature-Programmed Desorption, Main-Group Thermochemistry, Self-Interaction Error, Periodic Ab-Initio, Noncovalent Interactions, Density Functionals, Hydroxyl Radicals, Transition-Metal, Monoclinic Zirconia
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-119801 (URN)10.1039/c3cp44559c (DOI)000316467800030 ()23460024 (PubMedID)2-s2.0-84875478707 (Scopus ID)
Funder
Swedish Foundation for Strategic Research
Note

QC 20130322

Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2017-12-06Bibliographically approved
6. Enhanced hydrogen formation during the catalytic decomposition of H2O2 on metal oxide surfaces in the presence of HO radical scavengers
Open this publication in new window or tab >>Enhanced hydrogen formation during the catalytic decomposition of H2O2 on metal oxide surfaces in the presence of HO radical scavengers
2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 30, 12674-12679 p.Article in journal (Refereed) Published
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.

Keyword
Hydroxyl Radicals, Mgo(100) Surfaces, Methylene-Blue, Peroxide, Water, Reactivity, Tio2(110), Mechanism, Energy, DFT
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-119807 (URN)10.1039/c3cp51616d (DOI)000321622500034 ()2-s2.0-84881139845 (Scopus ID)
Note

QC 20130814

Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2017-12-06Bibliographically approved
7. Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides
Open this publication in new window or tab >>Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides
2013 (English)In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 379, 178-184 p.Article in journal (Refereed) Published
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.

Keyword
Catalysis, Hydroxyl, Oxide, Peroxide, Surface
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-119808 (URN)10.1016/j.molcata.2013.08.017 (DOI)000326772700024 ()2-s2.0-84884191958 (Scopus ID)
Note

QC 20131029

Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2017-12-06Bibliographically approved
8. Application of reactivity descriptors to the catalytic decomposition of hydrogen peroxide at oxide surfaces
Open this publication in new window or tab >>Application of reactivity descriptors to the catalytic decomposition of hydrogen peroxide at oxide surfaces
2015 (English)In: Computational and Theoretical Chemistry, ISSN 2210-271X, E-ISSN 2210-2728, Vol. 1070, 108-116 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-119809 (URN)10.1016/j.comptc.2015.08.001 (DOI)000361576000016 ()2-s2.0-84941272843 (Scopus ID)
Note

Updated from "In press" to "Published". QC 20151207. QC 20160304

Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2017-12-06Bibliographically approved

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