| 1. |
- Acke, Filip, et al.
(författare)
-
Study of the reduction and reoxidation of a CaO surface
- 1997
-
Ingår i: J Phys Chem B. - 1520-5207 .- 1520-6106. ; 101:33, s. 6484-
-
Tidskriftsartikel (refereegranskat)abstract
- The reduction of NO with CO and H2 is shown to comprise two basic reactions: a surface oxygen abstraction by the reducing agent and a reoxidation of the surface by NO. The former reaction step has been demonstrated by transient CO2 formation during CO exposure of oxidized CaO surfaces, while the latter was demonstrated by N2 and/or N2O transient formation during NO exposure of a prereduced CaO surface. It was shown that at low temperatures (between room temperature and 500 °C) both N2 and N2O were formed, but at temperatures above 500 °C only N2 was observed. The activation energies of the respective steps have been determined using temperature-programmed reaction experiments. The activation energy of the surface oxygen abstraction was determined to be 25 kcal/mol and is similar to the apparent activation energy of the overall reaction. The activation energy of the NO bond breakage was determined to be maximum 10 kcal/mol as measured by N2O formation. The importance of an N2O2- or N2O22- intermediate in the formation of N2O will be discussed, and the importance of N2O decomposition in forming N2 at temperatures above 500 °C will be compared with a N surface diffusion mechanism.
|
|
| 2. |
- Björnström, Joakim, 1976, et al.
(författare)
-
Antagonistic effect of superplasticizer and colloidal nano-silica in the hydration of Alite and Belite pastes
- 2007
-
Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 42:11, s. 3901-3907
-
Tidskriftsartikel (refereegranskat)abstract
- The dependence on the hydration rate for Alite and Belite clinker phases in the presence of a polycarboxylate superplasticizer PC SP upon addition of colloidal nano-silica CNS were monitored by means of Diffuse Reflectance Infrared spectroscopy DR-FTIR. Spectral signatures of clinker dissolution and product formation were acquired for both materials. The rates for the build-up of product vibrational band intensities were found to depend sensitively on addition of CNS. The hydration product was proposed to be calcium-silicate-hydrate C-S-H. Details in the spectral signatures were found to differ. Quantum chemical calculations were employed and found to be consistent with the interpretation that small clusters dominate the Alite C-S-H spectrum, whereas the Belite C-S-H spectrum results from extended polymers.
|
|
| 3. |
- Brülls, Steffen, 1991, et al.
(författare)
-
Bonding between π-Conjugated Polycations and Monolayer Graphene: Decisive Role of Anions
- 2023
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:4, s. 1917-28
-
Tidskriftsartikel (refereegranskat)abstract
- Functionalization and precise modulation of the electronic properties of graphene are key processes in the development of new applications of this promising material. This study examines the potential of using organic polycations as p-dopants and/or anchoring motifs for non-covalent functionalization. A library of hybrid materials was prepared through wet-chemical non-covalent functionalization. Both chemical vapor deposition graphene and reduced graphene oxide were functionalized with a series of neutral and polycationic benzimidazole-based systems. We report on how both the number of anions and the size, shape, and magnitude of the positive charge of the benzimidazole-based systems cooperatively affect the redox properties as well as the affinity for and the nature of bonding to graphene. The redox properties of the benzimidazole-based systems were studied by cyclic voltammetry. The functionalized graphene materials were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Density functional theory calculations were performed to make contact between the experimental results obtained for molecular samples and hybrid materials. No universal dependence of the binding affinity on a single parameter, such as the amount of positive charge or the size of the system, was found. Instead, the cooperative effect of the three-dimensional structure of the benzimidazole-based systems and the number of anions was found to play a pivotal role. Together, these parameters determine the degree of partial electron sharing and magnitude of dispersion forces involved in the binding of members of this family of benzimidazole-based systems to graphene.
|
|
| 4. |
- Busch, Michael, 1983, et al.
(författare)
-
Electrocatalytic Oxygen Evolution from Water on a Mn(III-V) Dimer Model Catalyst - A DFT Perspective
- 2011
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9076 .- 1463-9084. ; 13, s. 15069-15076
-
Tidskriftsartikel (refereegranskat)abstract
- A complete water oxidation and oxygen evolution reaction (OER) cycle is monitored by means of Density Functional Theory (DFT). A biomimetic model catalyst is employed, comprising a m-OH bridged Mn(III-V) dimer truncated by acetylacetonate ligand analogs and hydroxides. The reaction cycle is divided into four electrochemical hydrogen abstraction steps followed by a series of chemical steps. The former employ the Tyrosine/Tyrosyl radical acting as electron and proton sink thus determining the reference potential. Stripping hydrogen from water leads to the formation of two highly unstable Mn(V)=O/Mn(IV)-O· moieties, which subsequently combine to form a peroxy O-O bond. O2 evolution results from subsequent consecutive replacement of remaining Mn-O bonds by water. Conditions for the validities of GGA DFT and self-interaction error corrected hybrid DFT predictions despite the presence of a manifold of near-degenerate spin states, are discussed in some detail. The applicability of the former is extended to include the rate limiting steps in the OER.
|
|
| 5. |
- Busch, Michael, 1983, et al.
(författare)
-
Hydroxide Oxidation and Peroxide Formation at Embedded Binuclear Transition Metal Sites; TM=Cr, Mn, Fe, Co
- 2011
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9076 .- 1463-9084. ; 13, s. 15062-15068
-
Tidskriftsartikel (refereegranskat)abstract
- Key steps in electro-catalytic water oxidation on binuclear Transition Metal (TM) sites are addressed. These comprise (a) two one-electron oxidation steps of TM-OH moieties to form the corresponding two TM=O oxy-groups, and (b) a chemical step whereby the two oxy-species form a TM-O-O-TM peroxy-bridge. A test rig representing a generic low crystal field oxide support is described and employed. The energetics for said reactions are compared for homo-nuclear Cr(IIIV), Mn(III-V), Fe(II-IV) and Co(II-IV) sites. The uniqueness of the TyrO/TyrOH reference potential for driving said oxidation steps is demonstrated. Hydroxide oxidation on binuclear Mn and Co candidates require an overpotential of approximately 0.5 V relative to the chosen reference potential. Correspondingly, the subsequent O-O bond formation becomes strongly exothermic of the order of 1 eV. Hydroxide oxidation on binuclear CrCr and FeFe systems are exothermic by 0.2-0.4 eV relative to the TyrO/TyrOH reference potential. Consequently, the chemical step for transforming the TM=O moieties to the peroxo species is found to be endothermic on the order of 0.7 eV. These findings suggest that hetero-binuclear sites containing one TM from each class would be optimal. The validity of this concept is demonstrated for the FeCo binuclear site. The results are discussed in the context of experimental observations, which display preference for mixed oxide systems.
|
|
| 6. |
- Busch, Michael, 1983, et al.
(författare)
-
Validation of binuclear descriptor for mixed transition metal oxide supported electrocatalytic water oxidation
- 2013
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 202:1, s. 114-119
-
Tidskriftsartikel (refereegranskat)abstract
- The energy profiles of the di-hydroxo – di-oxo – peroxo pathway are discussed for a set of 3d transition metal oxides comprising V(III–V), Cr(III–V), Mn(II–IV, Mn(III–V), Fe(II–IV), Co(II–IV) and Ni(II–IV) using density functional theory (DFT). Two classes of oxides were identified. The first class, comprising V(III–V), Cr(III–V) and Fe(II–IV), displays exothermicity for the oxidation of di-hydroxo to di-oxo versus the tyrosine/tyrosyl-radical (TyrOH/TyrO) couple and endothermicity for the subsequent O-O bond formation ([−/+] class), while the second class, comprising Mn(III–V), Co(II–IV) and Ni(II–IV), shows endothermicity with respect to the oxidation step and exothermicity for the O-O bond formation ([+/−] class). The energetics of the endothermicity (exothermicity) for the oxidation step is reflected in the exothermicity (endothermicity) of the subsequent O-O bond formation step. Mn(II–IV) is not part of any of the two classes. Instead it shows zero exothermicity with respect to TyrOH/TyrO for the oxidation step and a small endothermicity for the O-O bond formation step. Despite the promising energy profile Mn(II–IV) is argued to be inactive due to a large activation barrier. A set of improved hetero-nuclear candidate catalysts is predicted by mixing [−/+] with [+/−] transition metal oxides. A simple and efficient method to estimate the energy profile of mixed transition metal oxides from the homo-nuclear systems is demonstrated. The validity of this procedure is checked and agreement with the explicitly calculated values is found. All considered heteronuclear candidate catalysts display enhanced performance compared to the pure homonuclear systems.
|
|
| 7. |
- Busch, Michael, 1983, et al.
(författare)
-
Water Oxidation on MnOx and IrOx: Why Similar Performance?
- 2013
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:1, s. 288-292
-
Tidskriftsartikel (refereegranskat)abstract
- The critical steps in water oxidation at a binuclear Mn(II–IV) oxide site are revisited. Ideal stabilities of intermediates are confirmed by comparing to results for a binuclear Ir(III–V) system. The latter in turn is known to be an excellent water oxidation catalyst. The inefficiency of the binuclear Mn(II–IV) site is owing to the high activation energy for the chemical step whereby MnIV═O double bonds on adjacent sites are broken prior to forming the MnIII—O—O—MnIII peroxy moiety. A rationale for Mn(II–IV)—Mn(III–V) mixed oxidation state for water oxidation catalysis, analogous to mixed transition metal oxide systems, is offered. Possible virtues of the kinetic stability of the binuclear MnIV═O moiety are discussed, utilizing its oxidizing power by sidestepping oxygen evolution.
|
|
| 8. |
- Bäcktorp, Carina, 1964, et al.
(författare)
-
Theoretical investigation of linalool oxidation.
- 2006
-
Ingår i: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 110:44, s. 12204-12
-
Tidskriftsartikel (refereegranskat)abstract
- This study concerns the autoxidation of one of the most used fragrances in daily life, linalool (3,7-dimethyl-1,6-octadien-3-ol). It reacts with O2 to form hydroperoxides, which are known to be important contact allergens. Pathways for hydroperoxide formation are investigated by means of quantum mechanical electronic structure calculations. Optimized molecular geometries and harmonic vibrational frequencies are determined using density functional theory (DFT). Insight into how the addition of O2 to linalool occurs is obtained by establishing a theoretical framework and systematically investigating three smaller systems: propene, 2-methyl-2-butene, and 2-methyl-2-pentene. 2-Methyl-2-pentene was chosen as a model system and used to compare with linalool. This theoretical study characterizes the linalool-O2 biradical intermediate state, which constitutes a branching point for the further oxidation reactions pathways. Thus, the observed linalool oxidation product spectrum is discussed in terms of a direct reaction path, the ene-type mechanism, and the radical mechanism. The major hydroperoxide found in experiments is 7-hydroperoxy-3,7-dimethyl-octa-1,5-diene-3-ol, and the calculated results support this finding.
|
|
| 9. |
- Campbell, Charles, et al.
(författare)
-
Catalyst design from theory to practice: general discussion
- 2016
-
Ingår i: Faraday Discussions. - 1359-6640 .- 1364-5498. ; 188, s. 279-307
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Hans-Joachim Freund opened the discussion of the paper by Alberto Roldan:How is the atomic hydrogen produced on the greigite surface? In the paper (DOI:10.1039/C5FD00186B) there is no comment whether you studied dissociatehydrogen adsorption.
|
|
| 10. |
- Chiragwandi, Zackary, 1968, et al.
(författare)
-
Ultraviolet driven negative current and rectifier effect in self assembled green fluorescent protein devices
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:16, s. 162909-1-162909-3
-
Tidskriftsartikel (refereegranskat)abstract
- UV induced negative current produced at low voltages is reported in a photocurrent rectifier device consisting of a sensing region between two nano Al/Al2O3 electrodes placed 30 nm apart, employing a droplet of enhanced green fluorescent protein as molecular electrolyte. The current-voltage characteristics are discussed in terms of the properties of the thin Al2O3 scale, the position of the Fermi level, the position of the highest occupied molecular orbital-lowest unoccupied molecular orbital gap, and dispersion of states induced by varying dielectric constants
|
|
