| 1. |
- Abdelgaid, Mona, et al.
(författare)
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Multiscale modeling reveals aluminum nitride as an efficient propane dehydrogenation catalyst
- 2023
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 13:12, s. 3527-3536
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Tidskriftsartikel (refereegranskat)abstract
- Nonoxidative propane dehydrogenation (PDH) is a promising route to meet the steadily increasing demand for propylene, an important building block in the chemical industry. Wurtzite group-IIIA metal nitrides are potential catalysts for PDH with high chemical, thermal, and mechanical stability alongside inherent Lewis acid-base properties that can activate the C-H bond of alkanes. Herein, we investigate the catalytic behavior of pristine (AlN) and gallium-doped (Ga/AlN) aluminum nitride for PDH via concerted and various stepwise mechanisms using density functional theory (DFT) calculations and microkinetic modeling (MKM). The reaction profiles investigated with DFT calculations are used in MKM, which reveals that the stepwise mechanisms produce >99% of propylene on both AlN and Ga/AlN. AlN has approximately one order of magnitude higher activity than Ga/AlN due to lower barriers along the dominant PDH reaction pathway. In summary, we propose the potential application of AlN as an efficient dehydrogenation catalyst for the conversion of light alkanes into valuable olefins. In addition, we show that multiscale simulations are essential to evaluate the catalytic behavior of complex alkane conversion reaction networks and obtain activity trends for dehydrogenation catalysts.
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| 2. |
- Abrahamsson, Brita, 1989, et al.
(författare)
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NOx Adsorption on ATiO(3)(001) Perovskite Surfaces
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:32, s. 18495-18503
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations have been used to explore NO adsorption on perovskite oxides surfaces ATiO(3)(001) with A = Ca, Sr, Ba. NO adsorbs weakly on all facets with no apparent A-ion dependence, whereas NO2 adsorbs preferably over AO-terminated surfaces with adsorption energies that correlate with the ionization potentials of the alkaline earth atoms. Simultaneous adsorption of NO and NO2 is found to substantially enhance the stability of the adsorbates owing to an oxide mediated electron-pairing mechanism. Stabilization is also predicted for NO/O-2 adsorption, and it is suggested that the presence of oxygen favors the formation of nitrite/nitrate pairs. It is found that the NOx adsorption properties can be modified by mixing alkaline earth cations in the perovskite framework. The results are put in context by comparison with NOx adsorption on the corresponding (001) facets of alkaline earth metal oxides and TiO2(110).
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| 3. |
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| 4. |
- Akola, J., et al.
(författare)
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Thiolate-Protected Au-25 Superatoms as Building Blocks: Dimers and Crystals
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:38, s. 15986-15994
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Tidskriftsartikel (refereegranskat)abstract
- A particularly stable thiolate-protected gold nanocluster, Au-25(SR)(18), was structurally characterized from X-ray crystallography in 2008, and concomitantly its electronic and optical properties were analyzed via density functional theory. The robust geometry and a well-understood electronic structure of this cluster motivate explorations of properties of extended systems made out of Au-25(SR)(18) building blocks. As a first step in this direction, we analyze here structural, vibrational, electronic, and optical properties of the Au-25 cluster anion as it was observed in the crystalline environment and predict properties of cluster dimers, where the Au-25 units are linked together. via an aromatic dithiolate linker. We show that properties of each Au-25 unit of the dimer can be quite independently modified from the other by doping with a nonmagnetic (Pd) or magnetic (Mn) metal atom. We anticipate that material systems with interesting properties could be made from these building blocks, provided that a suitable chemistry for their controlled linking can be found.
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| 5. |
- Arvidsson, Adam, 1990, et al.
(författare)
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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
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:7, s. 1470-1477
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
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| 7. |
- Baran, Jakub, 1980, et al.
(författare)
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Analysis of Porphyrines as Catalysts for Electrochemical Reduction of O-2 and Oxidation of H2O
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:4, s. 1320-1326
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Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Baran, J. D., et al.
(författare)
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Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 112:14
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Tidskriftsartikel (refereegranskat)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.
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| 9. |
- Baumann, S. O., et al.
(författare)
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Size Effects in MgO Cube Dissolution
- 2015
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 31:9, s. 2770-2776
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Tidskriftsartikel (refereegranskat)abstract
- Stability parameters and dissolution behavior of engineered nanomaterials in aqueous systems are critical to assess their functionality and fate under environmental conditions. Using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we investigated the stability of cubic MgO particles in water. MgO dissolution proceeding via water dissociation at the oxide surface, disintegration of Mg2+-O2- surface elements, and their subsequent solvation ultimately leads to precipitation of Mg(OH)(2) nanosheets. At a pH >= 10, MgO nanocubes with a size distribution below 10 nm quantitatively dissolve within few minutes and convert into Mg(OH)(2) nanosheets. This effect is different from MgO cubes originating from magnesium combustion in air. With a size distribution in the range 10 nm
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| 10. |
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