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Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-0086-5536
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0663-0751
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.

Place, publisher, year, edition, pages
2013. Vol. 379, 178-184 p.
Keyword [en]
Catalysis, Hydroxyl, Oxide, Peroxide, Surface
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-119808DOI: 10.1016/j.molcata.2013.08.017ISI: 000326772700024Scopus ID: 2-s2.0-84884191958OAI: oai:DiVA.org:kth-119808DiVA: diva2:612596
Note

QC 20131029

Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Reactions of aqueous radiolysis products with oxide surfaces: An experimental and DFT study
Open this publication in new window or tab >>Reactions of aqueous radiolysis products with oxide surfaces: An experimental and DFT study
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
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:nbn:se:kth:diva-119780 (URN)978-91-7501-683-2 (ISBN)
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
2. Oxidative dissolution of doped UO2 and H2O2 reactivity towards oxide surfaces: A kinetic and mechanistic study
Open this publication in new window or tab >>Oxidative dissolution of doped UO2 and H2O2 reactivity towards oxide surfaces: A kinetic and mechanistic study
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Oxidative dissolution of std. UO2 and UO2 doped with Cr2O3 and Al2O3, i.e. ADOPT, induced by H2O2 and γ radiation has been the main focus in this licentiate thesis. The catalytic decomposition of H2O2 on oxides like Gd2O3, HfO2, CeO2, Fe2O3 and CuO were also investigated.

A kinetic study was performed by determining first and second order rate constants together with Arrhenius parameters for the decomposition of H2O2. The reactivity of H2O2 towards the oxides mentioned was observed to differ significantly despite their similarities. In the mechanistic study, the yields and dynamics of the formation of the intermediate hydroxyl radical from the decomposition of H2O2 was determined for the oxides and found to differ considerably. A turnover point could be found for most of oxides studied, i.e. an increase in the rate of hydroxyl radical scavenging after a specific amount of consumed H2O2.

The reactivity of the std. UO2 and ADOPT towards H2O2 was similar to what was observed for other UO2-based materials in previous studies. The oxidative dissolution in radiation experiments showed a slight but significant difference. This was attributed to a difference in exposed surface area instead of an effect of doping. The difference in oxidative dissolution yield was too small to be significant which supports the previous conclusion.

Leaching experiments using spent nuclear fuel were also performed on the two types of fuel showing the same behavior as the unirradiated pellets, i.e., a slightly lower 238U release from ADOPT. The difference was attributed to difference in exposed surface area. The release of fission products with low UO2 solubility displayed a higher release from ADOPT which was attributed to a difference in matrix solubility. Cs was released to a larger extent from std. UO2. This is attributed to the larger grain size of ADOPT, extending the diffusion distance. The release of lanthanides and actinides was slightly higher for the conventional UO2, nevertheless the difference was relatively small.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. x, 51 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:23
Keyword
Oxidative dissolution; UO2; ADOPT; H2O2; Spent Nuclear Fuel.
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-145691 (URN)978-91-7595-149-2 (ISBN)
Presentation
2014-06-10, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140527

Available from: 2014-05-27 Created: 2014-05-26 Last updated: 2014-05-27Bibliographically approved
3. Radiation Induced Processes at Solid-Liquid Interfaces
Open this publication in new window or tab >>Radiation Induced Processes at Solid-Liquid Interfaces
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the thesis, the reactions between water radiolysis products—H2O2, HO• and O2—with metals and metal oxides utilized in nuclear industry are studied. The reactions include not only surface reactions, e.g. redox reactions and catalytic decomposition of H2O2, but also solution reactions (Haber-Weiss reactions). To study the interfacial reactions, it is crucial to monitor the dissolution of the solid material, reactivity of H2O2 and formation of the intermediate hydroxyl radicals.Hydroxyl radicals are captured by probe (Tris or methanol) to generate CH2O which can be quantified by the modified Hantzsch method. The results from γ-irradiation experiments on homogeneous system show that the conversion yield of CH2O from hydroxyl radicals is affected by O2 and pH. A mechanism of CH2O production from Tris is proposed.Besides, the consumption rate of H2O2 in the H2O2/ZrO2/Tris system is found to be influenced by Tris. A mechanism for the catalytic decomposition of H2O2 upon ZrO2 surface is proposed which includes independent surface adsorption sites for H2O2 and Tris. Moreover, it is demonstrated that the deviation of detected CH2O concentration by the modified Hantzsch method from actual concentration increases with increasing [H2O2]0/[CH2O]0.The inhibition of sulfide on the radiation induced dissolution of UO2 is confirmed and is dependent on sulfide concentration. And the inhibition of sulfide is independent to that of H2/Pd.It is found that the reactivity of H2O2 and dynamics of CH2O formation are different for the studied materials in the H2O2/MxOy/Probe system. The kinetic parameters, such as rate constant, activation energy, frequency factors are determined.Both surface and solution reactions are observed in the aqueous W(s)/H2O2/Tris system. It is also demonstrated that Haber-Weiss reactions which produce HO• continuously are dominating. Furthermore, it is found that hydroxyl radicals are formed simultaneously during the dissolution of W in aerobic aqueous system.The knowledge conveyed by the thesis is relevant to nuclear technological applications, as well as the applications related in photocatalysis, biochemistry, corrosion science, catalysis and optics/electronics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 74 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:39
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-172421 (URN)978-91-7595-656-5 (ISBN)
Public defence
2015-09-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150826

Available from: 2015-08-26 Created: 2015-08-21 Last updated: 2015-08-26Bibliographically approved

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