| 1. |
- Arvidsson, Adam, 1990, et al.
(författare)
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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
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:17, s. 4573-4580
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Baltrusaitis, J., et al.
(författare)
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Geometry and Electronic Properties of Glycerol Adsorbed on Bare and Transition-Metal Surface-Alloyed Au(111): A Density Functional Theory Study
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:3, s. 1749-1757
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Baltrusaitis, J., et al.
(författare)
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Photoelectrochemical Hydrogen Production on alpha-Fe2O3 (0001): Insights from Theory and Experiments
- 2014
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 7:1, s. 162-171
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Hellman, Anders, 1974, et al.
(författare)
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Electro-oxidation of water on hematite: Effects of surface termination and oxygen vacancies investigated by first-principles
- 2015
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 640, s. 45-49
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Taifan, W., et al.
(författare)
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CH4 and H2S reforming to CH3SH and H-2 catalyzed by metal-promoted Mo6S8 clusters: a first-principles micro-kinetic study
- 2017
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:16, s. 3546-3554
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Tidskriftsartikel (refereegranskat)abstract
- Direct processing of sour, e.g. containing large amounts of acidic H2S and/or CO2 molecules, natural gas is of direct interest as vast amounts of it are available and accessible but are underutilized. While sour natural gas is still treated using energy-intensive amine absorption/desorption, here we propose and describe a first step in catalytically producing a value added chemical and energy carrier, CH3SH and H-2, respectively. For this purpose, we performed Density Functional Theory (DFT) and microkinetic modelling of CH4 and H2S reaction pathways to form CH3SH and H-2 as a first step in elucidating complex yet not explored pathways in oxygen-free sour gas reforming. For this purpose, we utilized bare unpromoted and K-or Nipromoted Mo6S8 clusters. CH4 dissociation was found to be the rate-determining step above 1100 K on Ni-promoted Mo6S8 while H-2 formation was the rate-determining step on the bare and K-promoted Mo6S8. At lower reaction temperatures between 800 and 1100 K, CH3SH formation becomes an important step, especially on Ni-Mo6S8. This method presents an interesting route of direct catalytic sour natural gas processing which potentially leads to high-value hydrocarbons, such as ethylene, using CH3SH as a reactive intermediate.
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