SwePub - search: WFRF:(Hellman Anders 1974)

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1.	Zhang, Chu, et al. (author) Steps and catalytic reactions : CO oxidation with preadsorbed O on Rh(553) 2022 In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 715 Journal article (peer-reviewed)abstract Industrial catalysts are often comprised of nanoparticles supported on high-surface-area oxides, in order to maximise the catalytically active surface area and thereby utilise the active material better. These nanoparticles expose steps and corners that, due to low coordination to neighboring atoms, are more reactive and, as a consequence, are often assumed to have higher catalytic activity. We have investigated the reaction between CO and preadsorbed O on a stepped Rh(553) surface, and show that CO oxidation indeed occurs faster than on the flat Rh(111) surface at the same temperature. However, we do find that this is not a result of reactions at the step sites but rather at the terrace sites close to the steps, due to in-plane relaxation enabled by the step. This insight can provide ways to optimize the shape of the nanoparticles to further improve the activity of certain reactions.
2.	Adams, Emma, 1989, et al. (author) Structure-function relationship for alumina supported platinum during formation of ammonia from nitrogen oxide and hydrogen in presence of oxygen 2016 In: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 18:16, s. 10850-10855 Journal article (peer-reviewed)abstract We study the structure-function relationship of alumina supported platinum during forma- tion of ammonia from nitrogen oxide and dihydrogen by employing in situ X-ray absorption and Fourier transformed infrared spectroscopy. Particular focus is directed towards the effect of increased levels of oxygen on the reaction as a model system for emerging technologies for passive selective catalytic reduction of nitrogen oxides. The suppressed formation of ammo- nia observed as the feed becomes net-oxidizing is accompanied by a considerable increase in the oxidation state of platinum as well as enhanced formation of surface nitrates and loss of NH-containing surface species. In the presence of (excess) oxygen, the ammonia formation is proposed to be limited by the weak interaction between nitrogen oxide and the oxidized platinum surface. This leads to slow dissociation rate of nitrogen oxide and thus low abun- dance of atomic nitrogen surface species that can react with adsorbed hydrogen atoms. In this case the consumption of hydrogen through the competing water formation reaction and decomposition/oxidation of ammonia are of less importance for the net ammonia formation.
3.	Arvidsson, Adam, 1990, et al. (author) Metal dimer sites in ZSM-5 zeolite for methane-to-methanol conversion from first-principles kinetic modelling: is the [Cu-O-Cu]2+ motif relevant for Ni, Co, Fe, Ag, and Au? 2017 In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:7, s. 1470-1477 Journal article (peer-reviewed)abstract Direct methane-to-methanol conversion is a desired process whereby natural gas is transformed into an energy-rich liquid. It has been realised at ambient pressure and temperature in metal ion-exchanged zeolites, where especially copper-exchanged ZSM-5 has shown promising results. The nature of the active sites in these systems is, however, still under debate. The activity has been assigned to a [Cu-O-Cu]2+ motif. One remaining question is whether this motif is general and also active in other metal-exchanged zeolites. Herein, we use first-principles microkinetic modelling to analyse the methane-to-methanol reaction on the [Cu-O-Cu]2+ motif, for Cu and other metals. First, we identify the cluster model size needed to accurately describe the dimer motif. Starting from the [Cu-O-Cu]2+ site, the metal ions are then systematically substituted with Ni, Co, Fe, Ag and Au. The results show that activation of Ag and Au dimer sites with oxygen is endothermic and therefore unlikely, whereas for Cu, Ni, Co and Fe, the activation is possible under realistic conditions. According to the kinetic simulations, however, the dimer motif is a plausible candidate for the active site for Cu only. For Ni, Co and Fe, close-to-infinite reaction times or unreasonably high temperatures are required for sufficient methane conversion. As Ni-, Co- and Fe-exchanged ZSM-5 are known to convert methane to methanol, these results indicate that the Cu-based dimer motif is not an appropriate model system for these metals.
4.	Arvidsson, Adam, 1990, et al. (author) Partial oxidation of methane to methanol over ZSM-5 from first-principles 2016 In: ACS, San Diego, USA, March, 2016. Conference paper (peer-reviewed)
5.	Feng, Yanyue, 1993, et al. (author) Synthesis and Characterization of Catalytically Active Au Core─Pd Shell Nanoparticles Supported on Alumina 2022 In: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 38:42, s. 12859-12870 Journal article (peer-reviewed)abstract A two-step seeded-growth method was refined to synthesize Au@Pd core@shell nanoparticles with thin Pd shells, which were then deposited onto alumina to obtain a supported Au@Pd/Al2O3 catalyst active for prototypical CO oxidation. By the strict control of temperature and Pd/Au molar ratio and the use of l-ascorbic acid for making both Au cores and Pd shells, a 1.5 nm Pd layer is formed around the Au core, as evidenced by transmission electron microscopy and energy-dispersive spectroscopy. The core@shell structure and the Pd shell remain intact upon deposition onto alumina and after being used for CO oxidation, as revealed by additional X-ray diffraction and X-ray photoemission spectroscopy before and after the reaction. The Pd shell surface was characterized with in situ infrared (IR) spectroscopy using CO as a chemical probe during CO adsorption-desorption. The IR bands for CO ad-species on the Pd shell suggest that the shell exposes mostly low-index surfaces, likely Pd(111) as the majority facet. Generally, the IR bands are blue-shifted as compared to conventional Pd/alumina catalysts, which may be due to the different support materials for Pd, Au versus Al2O3, and/or less strain of the Pd shell. Frequencies obtained from density functional calculations suggest the latter to be significant. Further, the catalytic CO oxidation ignition-extinction processes were followed by in situ IR, which shows the common CO poisoning and kinetic behavior associated with competitive adsorption of CO and O2 that is typically observed for noble metal catalysts.
6.	Gustafsson, Johan, et al. (author) Low-temperature methane oxidation over single crystal Pd(100) 2012 In: 9th International Congress on Catalysis and Automotive Pollution Control (CAPoC9), Brussels, Belgium, August 29-31. Conference paper (peer-reviewed)
7.	Hellman, Anders, 1974, et al. (author) The Active Phase of Palladium during Methane Oxidation 2012 In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 3:6, s. 678-682 Journal article (peer-reviewed)abstract The active phase of Pd during methane oxidation is a long- standing puzzle, which, if solved, could provide routes for design of improved catalysts. Here, density functional theory and in situ surface X-ray diffraction are used to identify and characterize atomic sites yielding high methane conversion. Calculations are performed for methane dissociation over a range of Pd and PdOx surfaces and reveal facile dissociation on either under-coordinated Pd sites in PdO(101) or metallic surfaces. The experiments show unambiguously that high methane conversion requires sufficiently thick PdO(101) films or metallic Pd, in full agreement with the calculations. The established link between high activity and atomic structure enables rational design of improved catalysts.
8.	Sauer, Christopher, 1993, et al. (author) Continuous isomerisation of 2,5-dimethylfuran to 2,4-dimethylfuran over Ga-silicate 2024 In: Chemistry - A European Journal. - 1521-3765 .- 0947-6539. ; 30:20 Journal article (peer-reviewed)abstract 2,4-dimethylfuran has a rare disubstitution pattern in the five-membered heterocyclic furan ring that is highly interesting chemically but challenging to access synthetically. We present a heterogeneously catalysed route to synthesise 2,4-dimethylfuran from commonly available 2,5-dimethylfuran using a zeolite packed-bed flow reactor. As supported by DFT calculations, the reaction occurs inside the zeolite channels, where the acid sites catalyse proton transfer followed by migration of a methyl group. The zeotype Ga-silicate (MFI type) appears superior to an aluminium-containing ZSM-5 by demonstrating higher selectivities and slower catalyst deactivation. This work provides new opportunities for the continuous valorisation of bio-feedstock molecules in the perspective of the emerging biorefinery era.
9.	Wang, Xueting, 1991, et al. (author) Characterization of Metal-Exchanged Zeolites for Direct Conversion of Methane to Methanol (DCMM) 2016 Conference paper (other academic/artistic)
10.	Wang, Xueting, 1991, et al. (author) Desorption products during linear heating of copper zeolites with pre-adsorbed methanol 2020 In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 22:13, s. 6809-6817 Journal article (peer-reviewed)abstract Desorption products from zeolites with medium (MFI) and small (CHA) pores and with and without ion-exchanged copper were studied during linear heating after the pre-adsorption of methanol using a chemical flow reactor with a gas phase Fourier transform infrared spectrometer. The methanol desorption profiles were deconvoluted and compared with those predicted from first-principles calculations. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to study the samples during methanol desorption following a step-wise increase of the sample temperature. It is shown that well-dispersed copper species in the Cu-zeolite samples interact more strongly with methanol and its derivatives as compared to the bare zeolites, resulting in methanol desorption at higher temperatures. Moreover, the introduction of Cu leads to CO formation and desorption in larger amounts at lower temperatures compared to the bare zeolites. The formation and desorption of dimethyl ether (DME) from pre-adsorbed methanol takes place at different temperatures depending on both the influence of Cu and the zeolite topology. The Cu sites in zeolites lead to higher DME formation/desorption temperatures, while a small shift of DME desorption towards higher temperatures is observed for the CHA framework structure compared to the MFI framework structure.
11.	Wang, Xueting, 1991, et al. (author) Dream Reaction Come True? Direct Conversion of Methane to Methanol over Cu-zeolites 2017 Conference paper (other academic/artistic)
12.	Wang, Xueting, 1991, et al. (author) Methanol Desorption From Cu-ZSM-5 Studied by In Situ Infrared Spectroscopy and First-Principles Calculations 2017 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:49, s. 27389-27398 Journal article (peer-reviewed)abstract The dynamic interaction of methanol and its derivatives with Cu-exchanged ZSM- 5 during methanol temperature programmed desorption from 30 to 450 ◦C has been investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and first-principles calculations. The results emphasize that defects in the framework structure of the zeolite and Brønsted acid sites constitute ion-exchange sites for Cu ions. The Cu sites introduced in ZSM-5 actively interact with methanol adsorbed at moderate temperature, i.e. below 250◦C, and take roles in further oxidation of the adsorbed species to formate and CO. Moreover, spectra recorded at higher temperatures, i.e. above 300◦C, after adsorption of methanol show strong interaction between methoxy groups and the zeolite framework, suggesting that under mild conditions proton extraction for methanol production during direct partial oxidation of methane to methanol over Cu-ZSM-5 is necessary.
13.	Wettergren, Kristina, 1974, et al. (author) Unravelling the Dependence of Hydrogen Oxidation Kinetics on the Size of Pt Nanoparticles by in Operando Nanoplasmonic Temperature Sensing 2015 In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:1, s. 574-580 Journal article (peer-reviewed)abstract We use a noninvasive nanoscale optical-temperature measurement method based on localized surface plasmon resonance to investigate the particle size-dependence of the hydrogen oxidation reaction kinetics on model supported Pt nanocatalysts at atmospheric pressure in operando. With decreasing average nanoparticle size from 11 down to 3 nm, the apparent reaction activation energy is found to increase from 0.5 up to 0.8 eV. This effect is attributed to an increase of the fraction of (100)-facet and edge and corner sites and their increasingly important role in the reaction with decreasing particle size.
14.	Zhang, Chu, et al. (author) Faceting of Rhodium(553) in Realistic Reaction Mixtures of Carbon Monoxide and Oxygen 2015 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:21, s. 11646-11652 Journal article (peer-reviewed)abstract We have investigated the gas composition-dependent faceting of a Rh(553) surface during catalytic CO oxidation under semirealistic reaction conditions using Surface X- ray Diffraction. We find that under stoichiometric CO and O2 conditions, the Rh(553) surface maintains its surface orientation without facet formation. In oxygen excess, the CO oxidation reaction becomes mass transfer limited by the CO diffusion, and the sur- face is observed to expose (331) or (11 ̄1) facets in coexistence with larger (111) terraces. The observed facet formation has previously been observed for pure O2 exposures of the Rh(553) surface, but at significantly lower O2 partial pressures. Surprisingly, in CO excess, which results in a CO poisoned surface with low activity, we instead find coexisting (110) and (111) facets. The reasons for and possible implications of the observed facetings are discussed.
15.	Albinsson, David, 1990, et al. (author) Copper catalysis at operando conditions - bridging the gap between single nanoparticle probing and catalyst-bed-averaging 2020 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1 Journal article (peer-reviewed)abstract In catalysis, nanoparticles enable chemical transformations and their structural and chemical fingerprints control activity. To develop understanding of such fingerprints, methods studying catalysts at realistic conditions have proven instrumental. Normally, these methods either probe the catalyst bed with low spatial resolution, thereby averaging out single particle characteristics, or probe an extremely small fraction only, thereby effectively ignoring most of the catalyst. Here, we bridge the gap between these two extremes by introducing highly multiplexed single particle plasmonic nanoimaging of model catalyst beds comprising 1000 nanoparticles, which are integrated in a nanoreactor platform that enables online mass spectroscopy activity measurements. Using the example of CO oxidation over Cu, we reveal how highly local spatial variations in catalyst state dynamics are responsible for contradicting information about catalyst active phase found in the literature, and identify that both surface and bulk oxidation state of a Cu nanoparticle catalyst dynamically mediate its activity.
16.	Arvidsson, Adam, 1990, et al. (author) Descriptor-based microkinetic modelling for methanol-to-DME in zeotypes 2018 Conference paper (other academic/artistic)abstract A descriptor-based approach to study the methanol-to-DME reaction in zeotypes from first-principles is herein used to investigate the different reaction mechanism by means of a mean-field microkinetic model. In this theoretical study we focus on Brønsted acidic zeotype catalysts. We demonstrate that the difference of OH stretch frequency for the bare site and when CO is adsorbed on the site is a good descriptor for the acidic strength of the site. Different types of zeotypes are herein studied; CHA, BEA and MFI zeolite frameworks, where besides the conventional Al exchange we also consider B, Ga and Fe exchanged structures, along with SAPO-34, Mg-AlPO-34, Zn-AlPO-34, and Ti-AlPO-34. These span a wide range of strength of the acidic sites. The top panel in the figure to the right shows the free energy landscape for the two main reaction mechanisms for BEA and B-BEA (which have quite different acidity). The concerted mechanism, where two methanol molecules adsorb simultaneously to form DME and water, is shown in lighter colours, and the stepwise mechanism, where one methanol dissociates to a methyl group, producing water, after which a second methanol molecule is adsorbed to form hydrogenated DME, which then easily dehydrogenates, is shown in the darker shades. The bottom panel in the figure shows the calculated turn-over frequency (TOF) for the two mechanisms as a function of temperature. This shows that the concerted mechanism is dominating at lower temperatures while the stepwise dominates at higher temperatures for both systems.
17.	Arvidsson, Adam, 1990, et al. (author) First-principles microkinetic study of methane and hydrogen sulfide catalytic conversion to methanethiol/dimethyl sulfide on Mo 6 S 8 clusters: Activity/selectivity of different promoters 2019 In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:17, s. 4573-4580 Journal article (peer-reviewed)abstract A large fraction of the global natural gas reserves is in the form of sour gas, i.e. contains hydrogen sulfide (H2S) and carbon dioxide (CO2), and needs to be sweetened before utilization. The traditional amine-based separation process is energy-intensive, thereby lowering the value of the sour gas. Thus, there is a need to find alternative processes to remove, e.g., hydrogen sulfide. Mo6S8 clusters are promising candidates for transforming methane (CH4) and hydrogen sulfide into methanethiol (CH3SH) and dimethyl sulfide (CH3SCH3), which are high-value sulfur-containing products that can be further used in the chemical industry. Here first-principles microkinetics is used to investigate the activity and selectivity of bare and promoted (K, Ni, Cl) Mo6S8. The results show that methanethiol is produced via two different pathways (direct and stepwise), while dimethyl sulfide is formed via a competing pathway in the stepwise formation of methanethiol. Moreover, there is an increase in activity and a decrease in selectivity when adding an electropositive promoter (K), whereas the reverse behaviour is observed when adding an electronegative promoter (Cl). When adding Ni there is also a decrease in activity and an increase in selectivity; however, Ni is acting as an electron donor. The results provide insights and guidance as to what catalyst formulation is preferred for the removal of hydrogen sulfide in sour gas.
18.	Arvidsson, Adam, 1990, et al. (author) Influence of Acidity on the Methanol-to-DME Reaction in Zeotypes: A First Principles-Based Microkinetic Study 2020 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:27, s. 14658-14663 Journal article (peer-reviewed)abstract Acidity is considered a key factor in zeotype-based catalysts. Here, the effect of acidity in the methanol-to-DME reaction is investigated using first-principles calculations and microkinetic modeling, thereby establishing a connection between acididity and kinetics. The CHA, MFI, and BEA frameworks are investigated, and the acidity of the Brønsted hydroxyl group is varied by exchanging a T-site Si with Al, B, Ga, and Fe in the zeolites, along with SAPO-34, Mg-AlPO-34, Zn-AlPO-34, and Ti-AlPO-34 zeotypes with the CHA structure, and as a result, the Brønsted hydroxyl group spans a wide range of acidity. Clear trends in adsorption and transition-state energies are found and by means of linear regression, we obtain scaling relations of relevant energies that are later used as input in a mean-field steady-state microkinetic model. This study confirms that both the shift in frequency of the Brønsted hydroxyl stretch, ΔfOH, caused by adsorption of CO and the ammonia adsorption energy, ΔEammonia, on the Brønsted site are equivalent descriptors for the acidity of the Brønsted acid site and the reactivity of the different zeotypes relevant for the methanol-to-DME reaction. It further shows that a full microkinetic model is needed to accurately describe the reaction over the whole range of temperatures. However, if focusing on low temperatures, where the associative mechanism is dominating the reaction, a simple rate-determining step model is actually able to describe the results with satisfying agreement (deviation of the rate by less than a factor of two).
19.	Arvidsson, Adam, 1990, et al. (author) Insight of the methanol-to-DME reaction from descriptor-based microkinetic modelling 2018 Conference paper (other academic/artistic)abstract Using a descriptor-based approach to study the methanol-to-DME reaction in zeotypes from first-principles, we investigate the different reaction mechanism through a microkinetic model. This theoretical study focuses on Brønsted acidic zeotype catalysts. We demonstrate that the shift in OH stretch frequency with and without CO adsorbed on the site is a good descriptor for the strength of the acid site. Different zeotypes were studied, namely CHA, BEA and MFI zeolite frameworks, where besides conventional Al exchange, we also consider B, Ga and Fe, along with SAPO-34, Mg-AlPO-34, Zn-AlPO-34, and Ti-AlPO-34. These span a wide range of strength of the acidic sites. The top figure shows the free energy landscape for the two main reaction mechanisms for BEA and B-BEA (which have quite different acidity), namely the concerted where two methanol molecules adsorb simultaneously to form DME and water, and the stepwise where one methanol dissociates to a methyl group, producing water. The bottom figure shows the calculated turn-over frequency (TOF) for the two mechanisms as a function of temperature. This shows that the concerted mechanism is dominating at lower temperatures while the stepwise dominates at higher temperatures for both systems.
20.	Arvidsson, Adam, 1990, et al. (author) Modelling partial oxidation of methane over ZSM-5 and Mo6S8 catalysts 2017 Conference paper (other academic/artistic)abstract Partial oxidation of methane is an interesting but difficult reaction. Experimentally, methane can be partially oxidized to methanol over metal-exchanged zeolites. In particular the ZSM-5 zeolite has been widely studied and has been shown to be active when exchanged with Cu, Ni, Co, and Fe [1-4]. A clear [Cu-O-Cu] 2+ candidate for active site for the methane-to-methanol reaction has been put forth for Cu-ZSM-5 [1,5]. A first question to ask is whether this [Cu-O-Cu] 2+ motif is generic and could work also with Cu interchanged with Ni, Co, or Fe. Herein, we employ first-principles calculations and micro-kinetic modelling to compare the performance of Ni, Co, and Fe in this motif to the Cu one. Our finding is that the methane-to-methanol reaction can only realistically happen for Cu on this motif. Thus, this particular motif can be excluded as an active site candidate for Ni-, Co-, and Fe-ZSM-5 [6]. Another catalyst that is interesting for partial methane oxidation is the Mo6S8 cluster. However, instead of the methane-to-methanol reaction we use H2S as an oxidant and transform methane into hydrogen and CH3SH. Using electronic structure calculations and mean-field micro-kinetic modelling to study this reaction, we successfully capture the experimentally observed trend, i.e. that promoting the Mo 6 S 8 cluster with K increases the selectivity towards CH 3 SH, and Ni enhances the hydrogen formation [7]. [1] M. H. Groothaert, P. J. Smeets, B. F. Sels, P. A. Jacobs and R. A. Schoonheydt, J. Am. Chem. Soc., 127, 1394–1395 (2005). [2] J. Shan, W. Huang, L. Nguyen, Y. Yu, S. Zhang, Y. Li, A. I. Frenkel and F. F. Tao, Langmuir, 30, 8558–8569 (2014). [3] N. V. Beznis, B. M. Weckhuysen, and J. H. Bitter, Catal. Lett., 136, 52–56 (2010). [4] E. V. Starokon, M. V. Parfenov, L. V. Pirutko, S. I. Abornev and G. I. Panov, J. Phys. Chem. C, 115, 2155–2161 (2011). [5] J. S. Woertink, P. J. Smeets, M. H. Groothaert, M. A. Vance, B. F. Sels, R. A. Schoonheydt, and E. I. Solomon, Proc. Natl. Acad. Sci. U. S. A., 106, 18908–18913 (2009). [6] A. A. Arvidsson, V. P. Zhdanov, P.-A. Carlsson, H. Grönbeck, and A. Hellman, Catal. Sci. Technol., 7, 1470, (2017). [7] O. Y. Gutiérrez, L. Zhong, Y. Zhu, J. A. Lercher, ChemCatChem, 5, 3249–3259 (2013).
21.	Baltrusaitis, J., et al. (author) Geometry and Electronic Properties of Glycerol Adsorbed on Bare and Transition-Metal Surface-Alloyed Au(111): A Density Functional Theory Study 2016 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:3, s. 1749-1757 Journal article (peer-reviewed)abstract Glycerol exists in large amounts owing to its role as a byproduct in biodiesel production, and thanks to its chemical composition, it can be converted into more high-value products, such as mono- and polyethers, esters, diols, acrolein, and others. Hence, predicting glycerol-reactive properties is of utmost importance for designing efficient catalytic processes for its selective (electro)catalytic transformations; however, such an understanding is still far from complete. In this work, we performed quantum chemical calculations to validate a range of dispersion-corrected functionals to accurately predict and interpret structural, electronic, and vibrational properties of glycerol adsorbed on bare and transition-metal surface-alloyed Au(111) surface. optB86b-vdW (van der Waals) was found to have the overall best agreement with experiments concerning lattice constant, bulk stress, surface energy, and methanol adsorption among PBE (Perdew-Burke-Ernzerhof), optB88-vdW, optPBE-vdW, vdW-DF (density functional), vdW-DF2 (density functional 2nd version), and vdW-BEEF (Bayesian error estimation functional). Glycerol adsorption energy is found to correlate well with the calculated d-band center of the transition-metal-containing Au(111) surface layer. OH stretching vibrations are found to be very sensitive of the surface-alloy atom and resulted in large shifts toward lower wavenumbers, when compared to those on bare Au(111). The latter results clearly show that adsorption of glycerol to surface-alloy atoms can be monitored in situ by infrared spectroscopy.
22.	Baltrusaitis, J., et al. (author) Photoelectrochemical Hydrogen Production on alpha-Fe2O3 (0001): Insights from Theory and Experiments 2014 In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 7:1, s. 162-171 Journal article (peer-reviewed)abstract The photoelectrochemical (PEC) decomposition of organic compounds in wastewater is investigated by using quantum chemical (DFT) methods to evaluate alternatives to water splitting for the production of renewable and sustainable hydrogen. Methanol is used as a model organic species for the theoretical evaluations of electrolysis on the surface of the widely available semiconductor hematite, alpha-Fe2O3, a widely studied photocatalyst. Three different alpha-Fe2O3 surface terminations were investigated, including the predominant surface found in aqueous electrolytes, (OH)(3)-R. The PEC oxidation of methanol is energetically downhill, producing CO2 and protons. The protons are reduced to hydrogen on the cathode. Experimental PEC measurements were also performed for several polyalcoholic compounds, glycerol, erythritol, and xylitol, on alpha-Fe2O3 as the photocatalyst and showed high incident-photon-to-current-efficiencies (IPCE) that were much greater than those of water splitting. Interestingly, high IPCEs were observed for hydrogen production from polyalcohols in the absence of any applied bias, which was not thought to be possible on hematite. These results support the potential application of PEC for hydrogen production by using widely available hematite for the PEC oxidation of selected components of organic wastewater present in large quantities from anthropogenic and industrial sources.
23.	Baran, Jakub, 1980, et al. (author) Analysis of Porphyrines as Catalysts for Electrochemical Reduction of O-2 and Oxidation of H2O 2014 In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:4, s. 1320-1326 Journal article (peer-reviewed)abstract Bioinspired structures are promising as improved catalysts for various redox reactions. One example is metal hangman-porphyrines (MHP), which recently have been suggested for oxygen reduction/evolution reaction (ORR/OER). The unique properties of the MHPs are attributed to both the hangman scaffold and the C6F5 side groups. Herein, the OER/ORR over various transition metal MHPs is investigated by density functional theory calculations within an electrochemical framework. A comparison of the reaction landscape for MHP, metal porphyrine (MP) and metaltetrafluorophenyloporphyrines (MTFPP), allow for a disentanglement of the different roles of the hangman motif and the side groups. In agreement with experimental studies, it is found that Fe and Co are the best MHP Metal centers to catalyze these reactions. We find that the addition of the three-dimensional moiety in the form of hangman scaffold does not break the apparently universal energy relation between OH and OOH intermediates. However, the hangman motif is found to stabilize the oxygen intermediate, whereas addition of C6F5 groups reduces the binding energy of all reaction intermediates. Our results indicate that the combination of these two effects allow new design possibilities for macromolecular systems with enhanced catalytic OER/ORR activity.
24.	Baran, J. D., et al. (author) Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum 2014 In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:14 Journal article (peer-reviewed)abstract A first-principles account of the observed limiting thickness of oxide films formed on aluminum during oxidizing conditions is presented. The results uncover enhanced bonding of oxygen to thin alumina films in contact with metallic aluminum that stems from charge transfer between a reconstructed oxide-metal interface and the adsorbed molecules. The first-principles results are compared with the traditional Cabrera-Mott (CM) model, which is a classical continuum model. Within the CM model, charged surface oxygen species and metal ions generate a (Mott) potential that drives oxidation. An apparent limiting thickness is observed as the oxidation rate decreases rapidly with film growth. The present results support experimental estimates of the Mott potential and film thicknesses. In contrast to the CM model, however, the calculations reveal a real limiting thickness that originates from a diminishing oxygen adsorption energy beyond a certain oxide film thickness.
25.	Boje, Astrid, 1991, et al. (author) First-principles-informed energy span and microkinetic analysis of ethanol catalytic conversion to 1,3-butadiene on MgO 2021 In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 11:20, s. 6682-6694 Journal article (peer-reviewed)abstract Kinetic modeling of single-step catalytic conversion of ethanol to 1,3-butadiene is necessary to inform accurate process design. This paper uses first-principles-informed energy span and microkinetic analysis to explore the reaction free energy landscapes and kinetic limitations of competing reaction pathways on a MgO (100) step-edge. Previous studies suggested mechanisms proceeding via both dehydrogenation and dehydration of ethanol, and highlighted sensitivity to conditions and catalyst composition. Here, we use the energy span concept to characterize the theoretical maximum turnover and degree of turnover frequency control for states in each reaction pathway, finding the dehydration route to be less active for 1,3-butadiene, and suggesting rate-determining states in the dehydrogenation, dehydration, and condensation steps. The influence of temperature on the relative rate contribution of each state is quantified and explained through the varying temperature sensitivity of the free energy landscape. A microkinetic model is developed to explore competition between pathways, interaction with gas-phase species, and surface coverage limitations. This suggests that the turnover may be significantly lower than predicted solely based on energetics. Turnover frequency determining states found to have high surface coverage include adsorbed ethanol and two longer, oxygenated hydrocarbons. The combined energy span and microkinetic analysis permits investigation of a complex system from two perspectives and helps elucidate conflicting observations of rate determining steps and product distribution by considering both energetic and kinetic limitations. The impact of uncertainty in the energy landscape is quantified using a correlated error model. While the range of predictions is large, the average performance and trends are similar.
26.	Brorsson, Joakim, 1988, et al. (author) Discovery of Oxygen Carriers by Mining a First-Principle Database 2023 In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:20, s. 9437-9451 Journal article (peer-reviewed)abstract Chemical looping is an innovative technique that relies, to a large extent, on the possibility of finding new oxygen carriers. Until now, these materials have primarily been identified via experimental techniques and therefrom derived insights. However, this is both costly and time-consuming. To speed-up this process, we have applied a computational screening approach based on energetic data retrieved from the Open Quantum Materials Database. In particular, we have considered combinations of all mono-, bi-, and trimetallic alloys and mixed oxides with up to three distinctive phases. Here, we specifically focus on a technique referred to as chemical looping oxygen uncoupling, which is especially suitable for solid fuels, e.g., combustion of biomass for negative CO2 emissions. The formation energies obtained for the materials of interest were used to identify phase transitions that are likely to occur under conditions relevant for chemical looping oxygen uncoupling. Given these criteria, the initial list of 300000 materials is reduced by a factor of 20, and after filtering out rare, radioactive, toxic, or harmful elements only 1000 remain. When considering the abundance of elements in the ranking criteria, most of the highest ranking phases include Cu, Mn, and Fe. This adds credibility to the procedure, as many viable oxygen carriers for chemical looping oxygen uncoupling that have been studied experimentally contain these elements. While Cr-based materials have not been widely explored for this application, our study suggests that this might be worthwhile since these occur more frequently than Fe. Other elements that would be interesting as additional components include Ba, K, Na, Al, and Si.
27.	Brorsson, Joakim, 1988, et al. (author) Thermodynamic properties for metal oxides from first-principles 2024 In: Computational Materials Science. - 0927-0256. ; 233 Journal article (peer-reviewed)abstract In this study, an efficient first-principles approach for calculating the thermodynamic properties of mixed metal oxides at high temperatures is demonstrated. More precisely, this procedure combines density functional theory and harmonic phonon calculations with tabulated thermochemical data to predict the heat capacity, formation energy, and entropy of important metal oxides. Alloy cluster expansions are, moreover, employed to represent phases that display chemical ordering as well as to calculate the configurational contribution to the specific heat capacity. The methodology can, therefore, be applied to compounds with vacancies and variable site occupancies. Results are, moreover, presented for a number of systems of high practical relevance: Fe–K–Ti–O, K–Mn–O, and Ca–Mn–O. For the reference materials, the agreement with experimental measurements is exceptional in the case of ilmenite (FeTiO3) and good for CaMnO3. When the generated data is used in multi-phase thermodynamic calculations to represent materials for which experimental data is not available, the predicted phase-diagrams for the K–Mn–O and K–Ti–O systems change dramatically. The demonstrated methodology is highly useful for obtaining approximate values on key thermodynamic properties in cases where experimental data is hard to obtain, inaccurate or missing.
28.	Busch, Michael, 1983, et al. (author) The Influence of Inert Ions on the Reactivity of Manganese Oxides 2018 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:1, s. 216-226 Journal article (peer-reviewed)abstract Inert ion doping is a possible method to modify electrical conductivity and catalytic activity of transition-metal oxide electrocatalysts. Despite the importance of dopants, little is known about the underlying mechanisms for the change of the system properties. We have performed density functional theory calculations to investigate the influence of different valent ions on the O 2 evolution reaction activity of β-MnO 2 and Mn 2 O 3 . While Mn 2 O 3 is unaffected by dopants, β-MnO 2 is strongly affected by ions placed in a subsurface position. Doping does not affect the ion charge at the active site, but instead it effects the bond character. This is concluded through an analysis of the density overlap regions indicator and the density of states showing that the partially covalent nature of the bonds in β-MnO 2 is responsible for the changes in the adsorbate binding energies. This mechanism is not active in the mostly ionic Mn 2 O 3 . These results highlight the need to explicitly consider the detailed bonding situation and to go beyond simple charge transfer considerations when describing doping of transition metal oxide catalysts.
29.	Cusinato, Lucy, 1991, et al. (author) Structure and Composition Modification of Ultrasmall Palladium Nanoparticles upon Hydrogenation from First Principles 2019 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:30, s. 18609-18619 Journal article (peer-reviewed)abstract Palladium-based materials exhibit a high affinity for hydrogen, making them ideal candidates for hydrogen storage or hydrogen sensing applications owing to the existence of a hydride phase. From the theoretical point of view, a bulk or slab is often used to model such systems but lacks the flexibility to adapt its lattice parameter to an increased load of hydrogen. Using density functional theory, we follow the change in the structure and composition of small palladium nanoparticles upon hydrogenation. We show that a cuboctahedral nanoparticle with hydrogen in the core and on the surface is a relevant model under experimental conditions. CO and NO are then adsorbed on this nanoparticle to highlight the crucial importance of hydrogen loading when considering palladium nanomaterials for-wider sensing applications.
30.	Engedahl, Unni, 1990, et al. (author) Complete Reaction Cycle for Methane-to-Methanol Conversion over Cu-SSZ-13: First-Principles Calculations and Microkinetic Modeling 2021 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 14681-14688 Journal article (peer-reviewed)abstract The steadily increasing consumption of natural gas imposes a need to facilitate the handling and distribution of the fuel, which presently is compressed or condensed. Alternatively, reduced volatility and increased tractability are achieved by converting the chemical energy of the main component, methane, into liquid methanol. Previous studies have explored direct methane-to-methanol conversion, but suitable catalysts have not yet been identified. Here, the complete reaction cycle for methane-to-methanol conversion over the Cu-SSZ-13 system is studied using density functional theory. The first step in the reaction cycle is the migration of Cu species along the zeolite framework forming the Cu pair, which is necessary for the adsorption of O2. Methane conversion occurs over the CuOOCu and CuOCu sites, consecutively, after which the system is returned to its initial structure with two separate Cu ions. A density functional theory-based kinetic model shows high activity when water is included in the reaction mechanism, for example, even at very low partial pressures of water, the kinetic model results in a turnover frequency of ∼1 at 450 K. The apparent activation energy from the kinetic model (∼1.1 eV) is close to recent measurements. However, experimental studies always observe very small amounts of methanol compared to formation of more energetically preferred products, for example, CO2. This low selectivity to methanol is not described by the current reaction mechanism as it does not consider formation of other species; however, the results suggest that selectivity, rather than inherent kinetic limitations, is an important target for improving methanol yields from humid systems. Moreover, a closed reaction cycle for the partial oxidation of methane has long been sought, and in achieving this over the Cu-SSZ-13, this study contributes one more step toward identifying a suitable catalyst for direct methane-to-methanol conversion.
31.	Engedahl, Unni, 1990, et al. (author) First-principles study of oxidation state and coordination of Cu-Dimers in Cu-SSZ-13 during methane-to-methanol reaction conditions 2019 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:43, s. 26145-26150 Journal article (peer-reviewed)abstract Direct methane-to-methanol conversion is a dream reaction which presently can be realized via a three-step cycle over copper-exchanged zeolites; an activation phase, a reaction phase, and finally an extraction phase. Here we use ab initio molecular dynamics and first-principles thermodynamics to examine oxidation state and coordination of Cu-dimers in Cu-SSZ-13 under relevant experimental conditions. A multitude of Cu2(HxOy) clusters are exergonic at room temperature. However, at the relevant reaction conditions only Cu2O and Cu2(OH) remain as thermodynamically stable structures for the activation and extraction phase, respectively.
32.	Engedahl, Unni, 1990, et al. (author) Investigating the Composition of the Metal Dimer Site in Chabazite for Direct Methane-to-Methanol Conversion 2024 In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:9, s. 3641-3651 Journal article (peer-reviewed)abstract Methanol is a liquid energy carrier that has the potential to reduce the use of fossil fuels. Industrial production of methanol is currently a multistep high-temperature/high-pressure synthesis route. Direct conversion of methane to methanol under low-temperature and low-pressure conditions is an interesting but challenging alternative, which presently lacks suitable catalysts. Here, the complete reaction cycle for direct methane-to-methanol conversion over transition-metal dimers in the chabazite zeolite is studied by using density functional theory calculations and microkinetic modeling. In particular, a reaction mechanism previously identified for the Cu2 dimer is explored under dry and wet conditions for dimers composed of Ag, Au, Pd, Ni, Co, Fe, and Zn and the bimetallic dimers AuCu, PdCu, and AuPd. The density-functional-theory-based microkinetic modeling shows that Cu2, AuPd, and PdCu dimers have reasonable turnover frequencies under technologically relevant conditions. The adsorption energy of atomic oxygen is identified as a descriptor for the reaction landscape as it correlates with the adsorption and transition-state energies of the other reaction intermediates. Using the established scaling relations, a volcano plot of the rate is generated with its apex close to the Cu2, AuPd, and PdCu dimers.
33.	Engedahl, Unni, 1990, et al. (author) Reaction mechanism for methane-to-methanol in CU-SSZ-13: First-principles study of the Z 2 [Cu 2 O] and Z 2 [Cu 2 oh] motifs 2021 In: Catalysts. - : MDPI AG. - 2073-4344. ; 11:1, s. 1-12 Journal article (peer-reviewed)abstract As transportation continues to increase world-wide, there is a need for more efficient utilization of fossil fuel. One possibility is direct conversion of the solution gas bi-product CH4 into an energy-rich, easily usable liquid fuel such as CH3OH. However, new catalytic materials to facilitate the methane-to-methanol reaction are needed. Using density functional calculations, the partial oxidation of methane is investigated over the small-pore copper-exchanged zeolite SSZ-13. The reaction pathway is identified and the energy landscape elucidated over the proposed motifs Z2 [Cu2O] and Z2 [Cu2OH]. It is shown that the Z2[Cu2O] motif has an exergonic reaction path, provided water is added as a solvent for the desorption step. However, a micro-kinetic model shows that neither Z2 [Cu2O] nor Z2 [Cu2OH] has any notable activity under the reaction conditions. These findings highlight the importance of the detailed structure of the active site and that the most stable motif is not necessarily the most active.
34.	Fant, Magnus, et al. (author) To Every Rule There is an Exception: A Rational Extension of Loewenstein's Rule 2021 In: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 60:10, s. 5132-5135 Journal article (peer-reviewed)abstract Loewenstein's rule, which states that Al−O−Al motifs are energetically unstable, is fundamental to the understanding and design of zeolites. Here, using a combination of electronic structure calculations and lattice models, we show under which circumstances this rule becomes invalid and how it can be rationally extended using the chabasite framework for demonstration.
35.	Frondelius, P., et al. (author) Charging of atoms, clusters, and molecules on metal-supported oxides: A general and long-ranged phenomenon 2008 In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 78:8, s. 7- Journal article (peer-reviewed)abstract The density-functional theory is used to investigate the adsorption of Au atoms, Au clusters, and NO2 molecules on transition-metal-supported oxides. As compared to unsupported oxides, the adsorbates on supported oxide films are charged and experience a higher adsorption energy. The origin of the effect is explored by considering two different oxides (MgO and Al2O3) and a range of supporting metals. Moreover, the limits of the enhancement are probed by explicit calculations for thick MgO films and low coverage. The long-range character of the phenomenon is attributed to electrostatic polarization. The absolute strength depends on several contributions and their relative importance changes with system composition.
36.	Frost, Rickard, 1979, et al. (author) Core−Shell Nanoplasmonic Sensing for Characterization of Biocorona Formation and Nanoparticle Surface Interactions 2016 In: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 1:6, s. 798-806 Journal article (peer-reviewed)abstract Surface properties of nanoparticles imposed by particle size, shape, and surface chemistry are key features that largely determine their environmental fate and effects on biological systems. Consequently, development of analytical tools to characterize surface properties of nanomaterials and their relation to toxicological properties must occur in parallel with applications. As a contribution to this quest, we present a nanoplasmonic sensing strategy that enables systematic in situ characterization of molecule−nanoparticle interactions under well-controlled conditions, in terms of both nanoparticle size and surface chemistry, with particular focus on the importance of surface faceting in crystalline nanoparticles. We assess the performance of our sensing strategy by presenting two case studies. (i) The first is protein corona formation on faceted Au core−SiO2 shell nanoparticles of different sizes, and thus different surface facet-to-edge ratios. Based on 2D and 3D models of the investigated structures, we find that for small particles the curved regions between adjacent facets dominate the response of the corona formation process, whereas the facets dominate the response in the large particle regime. (ii) The second is in situ functionalization of Au core−SiO2 shell nanoparticle surfaces, and analysis of the subsequent protein repellent behavior. Due to the versatility of the presented sensing strategy in studies of nanoparticle surface properties, including in situ surface modifications, and their interactions with (bio)molecules during corona formation, we foresee it to become a valuable tool in the areas of nanomedicine and nanotoxicology.
37.	Grönbeck, Henrik, 1966, et al. (author) Low Temperature CO Oxidation over Supported Ultrathin MgO Films 2011 In: Proceedings of 22nd North American Catalysis Society Meeting, Detroit, USA, June 5-10, 2011. Conference paper (peer-reviewed)
38.	Grönbeck, Henrik, 1966, et al. (author) Mechanism for reversed photoemission core-level shifts of oxidized Ag 2012 In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 85:11 Journal article (peer-reviewed)abstract Density functional theory calculations and high-resolution core-level spectroscopy are used to explore the remarkable observation of decreased Ag 3d binding energy upon silver oxidation. The shift in Ag 3d binding energy is investigated at different degrees of oxidation and compared to results for Pd 3d, which exhibits a normal shift. Analysis of initial-state effects and valence electronic structure shows that the onsite Ag core potential is insensitive to oxidation despite a clear metal-to-oxygen charge transfer. The substantial negative shift for oxidized Ag is instead attributed to final-state effects as screening of the core-hole occurs in metal s states of bonding character.
39.	Grönbeck, Henrik, 1966, et al. (author) Structural, Energetic, and Vibrational Properties of NOx Adsorption on Agn, n = 1-8 2007 In: Journal of Physical Chemistry A. ; 111, s. 6062-6067 Journal article (peer-reviewed)
40.	Hagman, Benjamin, et al. (author) Steps Control the Dissociation of CO2 on Cu(100) 2018 In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 140:40, s. 12974-12979 Journal article (peer-reviewed)abstract CO2 reduction reactions, which provide one route to limit the emission of this greenhouse gas, are commonly performed over Cu-based catalysts. Here, we use ambient pressure X-ray photoelectron spectroscopy together with density functional theory to obtain an atomistic understanding of the dissociative adsorption of CO2 on Cu(100). We find that the process is dominated by the presence of steps, which promote both a lowering of the dissociation barrier and an efficient separation between adsorbed O and CO, reducing the probability for recombination. The identification of steps as sites for efficient CO2 dissociation provides an understanding that can be used in the design of future CO2 reduction catalysts.
41.	Hellman, Anders, 1974 (author) A detailed investigation of the active phase of palladium during methane oxidation 2012 In: 3S-symposium of surface science, St. Christoph, Austria, 11th March- 17th of March 2012. Conference paper (peer-reviewed)
42.	Hellman, Anders, 1974, et al. (author) Activation of Al2O3 by a Long-Ranged Chemical Bond Mechanism 2008 In: Physical Review Letters. ; 100:11, s. 116801- Journal article (peer-reviewed)
43.	Hellman, Anders, 1974, et al. (author) Ammonia Synthesis: State of the Bellwether Reaction 2013 In: Comprehensive Inorganic Chemistry II (Second Edition): From Elements to Applications. - 9780080965291 ; 7, s. 459-474 Book chapter (other academic/artistic)abstract Catalytic ammonia synthesis has been judged to be one of mankind's greatest scientific achievements during the twentieth century. The socioeconomic implications of producing ammonia industrially have been a strong driving force, and this development has spurred a range of new discoveries within physics, chemistry, and chemical engineering. In this chapter, we describe how it has been possible in recent years to provide a full understanding of the catalytic ammonia synthesis reaction at the atomic level through the combined use of experiments and quantum mechanical electronic structure calculations, thus clearly showing many of the reasons why ammonia synthesis has been, and still is, the bellwether reaction in heterogeneous catalysis.
44.	Hellman, Anders, 1974, et al. (author) Electro-oxidation of water on hematite: Effects of surface termination and oxygen vacancies investigated by first-principles 2015 In: Surface Science. - : Elsevier BV. - 0039-6028. ; 640, s. 45-49 Journal article (peer-reviewed)abstract The oxygen evolution reaction on hydroxyl- and oxygen-terminated hematite was investigated using first-principle calculations within a theoretical electrochemical framework. Both pristine hematite and hematite containing oxygen vacancies were considered. The onset potential was determined to be 1.79 V and 2.09 V vs. the reversible hydrogen electrode (RHE) for the pristine hydroxyl- and oxygen-terminated hematite, respectively. The presence of oxygen vacancies in the hematite surface resulted in pronounced shifts of the onset potential to 3.09 V and 1.83 V. respectively. Electrochemical oxidation measurements conducted on thin-film hematite anodes, resulted in a measured onset potential of 1.66 V vs. RHE. Furthermore, the threshold potential between the hydroxyl- and oxygen-terminated hematite was determined as a function of pH. The results indicate that electrochemical water oxidation on hematite occurs on the oxygen-terminated hematite, containing oxygen vacancies.
45.	Hellman, Anders, 1974 (author) First-principles insights of the active phase during catalytic reactions 2012 In: 15th Nordic symposium of catalysis, Mariehamn, Åland, 10th of June-12th of June. Conference paper (peer-reviewed)
46.	Hellman, Anders, 1974, et al. (author) First-principles studies of NOx chemistry on Agn/Al2O3 2009 In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 113, s. 3674-3682 Journal article (peer-reviewed)
47.	Hellman, Anders, 1974 (author) First-principles study of photoinduced water-splitting of Fe2O3 2011 In: NAM22, Detroit, USA, 5th-10th June, 2011. Conference paper (peer-reviewed)
48.	Hellman, Anders, 1974, et al. (author) First-Principles Study of Photoinduced Water-Splitting on Fe2O3 2011 In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:26, s. 12901-12907 Journal article (peer-reviewed)abstract Photoinduced water-splitting on hematite (Fe(2)O(3)) is investigated by first-principles calculations. (HO)(3)-Fe-H(3)O(3)-R, (HO)(3)-Fe-O(3)-R, O(3)-Fe-O(3)-R, (HO)(3)-Fe-R and O(3)-R terminations are considered, where R represents the bulk stacking sequence. The stability under photoelectrochemical conditions and the free energy of all reaction intermediates in a simple one-electron transfer reaction mechanism is calculated and the ability of different surface terminations to function as a photoanode is analyzed. Our results show that (i) under relevant photoelectrochemical conditions only O(3)-Fe-O(3)-R and O(3)-R are stable and that (ii) the water-oxidation is only allowed on (HO)(3)-Fe-H(3)O(3)-R, (HO)(3)-Fe-O(3)-R, O(3)-Fe-O(3)-R from thermodynamic considerations. The results suggest that hematite, as long as the (HO)(3)-Fe-H(3)O(3)-R termination is present under normal conditions, is a promising candidate for the photoanode.
49.	Hellman, Anders, 1974, et al. (author) First-Principles View on Photoelectrochemistry: Water-Splitting as Case Study 2017 In: Inorganics. - : MDPI AG. - 2304-6740. ; 5:2, s. Article no 37 - Research review (peer-reviewed)abstract Photoelectrochemistry is truly an interdisciplinary field; a natural nexus between chemistry and physics. In short, photoelectrochemistry can be divided into three sub-processes, namely (i) the creation of electron-hole pairs by light absorption; (ii) separation/transport on the charge carriers and finally (iii) the water splitting reaction. The challenge is to understand all three processes on a microscopic scale and, perhaps even more importantly, how to combine the processes in an optimal way. This review will highlight some first-principles insights to the above sub-processes, in particular as they occur using metal oxides. Based on these insights, challenges and future directions of first-principles methods in the field of photoelectrochemistry will be discussed.
50.	Hellman, Anders, 1974 (author) HC-assisted NOx reduction on Agn/Al2O3: a density functional theory study 2012 In: ECOSS 26, Parama, Italy, 30 August- 4 September 2009. Conference paper (peer-reviewed)

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