| 1. |
- Engedahl, Unni, 1990, et al.
(författare)
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Complete Reaction Cycle for Methane-to-Methanol Conversion over Cu-SSZ-13: First-Principles Calculations and Microkinetic Modeling
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 14681-14688
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Engedahl, Unni, 1990, et al.
(författare)
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Investigating the Composition of the Metal Dimer Site in Chabazite for Direct Methane-to-Methanol Conversion
- 2024
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:9, s. 3641-3651
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Jareteg, Adam, 1989, et al.
(författare)
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Effects of bed aging on temperature signals from fixed-bed adsorbers during industrial operation
- 2020
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Ingår i: Results in Engineering. - : Elsevier BV. - 2590-1230. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The capacity of adsorber beds used in industrial-scale temperature-swing adsorption diminishes over time due to bed aging. Here, we present industrial data on the temperature signals from fixed-bed adsorbers using activated carbon designed to remove benzene and other impurities from the gas produced in biomass gasification. The aging of the adsorber beds proceeds due to irreversible adsorption of trace species and manifests itself via two simultaneous effects: a decrease in the availability of active adsorption sites over time and an increase in the overall thermal mass of the bed. Both effects tend to dampen the temperature response of the beds during operation, implying that they are easily confounded. Model descriptions of bed aging should account for both effects.
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| 4. |
- Jareteg, Adam, 1989, et al.
(författare)
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Industrial-scale benzene adsorption: assessment of a baseline one-dimensional temperature swing model against online industrial data
- 2020
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 59:26, s. 12239-12249
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Tidskriftsartikel (refereegranskat)abstract
- Existing models for industrial gas cleaning via temperature-swing adsorption are typically validated against laboratory-scale test units, while industrial cases involve units that are significantly larger, operate with complex gas mixtures, and are cycled for long times. The extent up to which existing model formulations are applicable in industrial units is not well established. Here, we compare simulations with a baseline 1D model at an industrial scale to the online temperature data from steam-regenerated adsorbers in a 32 MW biomass gasification plant. Adsorption of benzene is described using the Dubinin–Radushkevich isotherm, and steam may condense/evaporate but not adsorb. The simulations reproduce the main trends in the industrial data, meaning that they can be used to assess dynamic properties that are not measured, such as the amounts of adsorbates and water. Additional model development is however needed to better represent the effects of complex gas mixtures and water transport and evaporation inside the beds.
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| 5. |
- Jareteg, Adam, 1989, et al.
(författare)
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Investigation of steam regeneration strategies for industrial-scale temperature-swing adsorption of benzene on activated carbon
- 2021
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Ingår i: Chemical Engineering and Processing: Process Intensification. - : Elsevier BV. - 0255-2701. ; 167
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale separation of substances present at low concentrations is readily performed by adsorption in packed beds that requires recurring energy-intensive regeneration of the adsorbent. The present work uses numerical simulations previously developed for industrial-scale packed-bed benzene sorption on activated carbon with temperature-swing regeneration by steam to investigate the influence of steam properties and regeneration strategy on total energy performance and breakthrough behaviour. It is shown that using saturated steam lowers both the steam mass and energy consumption during regeneration of a fixed amount of benzene, whereas using superheated steam returns the bed to a more fresh-like state after each regeneration stage. The most promising variation tried implies a 19% reduction in the energy consumption. Furthermore, the importance of accounting for the real industrial cycling conditions in the optimization of packed-bed adsorbers is highlighted. It is shown that the participation of different sections of the bed during adsorption varies with the regeneration strategy, but is never as localized as predicted from a model for a fresh bed without cycling. Finally, the present results also show that the effluent purity attained during regeneration increases when high-temperature saturated steam is used, e.g. a 60-degree increase in steam temperature raises the purity by 11%.
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| 6. |
- Levin, Sune, 1991, et al.
(författare)
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Nanofluidic Trapping of Faceted Colloidal Nanocrystals for Parallel Single-Particle Catalysis
- 2022
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Ingår i: Acs Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:9, s. 15206-15214
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst activity can depend distinctly on nano -particle size and shape. Therefore, understanding the structure sensitivity of catalytic reactions is of fundamental and technical importance. Experiments with single-particle resolution, where ensemble-averaging is eliminated, are required to study it. Here, we implement the selective trapping of individual spherical, cubic, and octahedral colloidal Au nanocrystals in 100 parallel nanofluidic channels to determine their activity for fluorescein reduction by sodium borohydride using fluorescence microscopy. As the main result, we identify distinct structure sensitivity of the rate-limiting borohydride oxidation step originating from different edge site abundance on the three particle types, as confirmed by first -principles calculations. This advertises nanofluidic reactors for the study of structure-function correlations in catalysis and identifies nanoparticle shape as a key factor in borohydride-mediated catalytic reactions.
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| 7. |
- Li, Tian, et al.
(författare)
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A fast-solving particle model for thermochemical conversion of biomass
- 2020
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Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 213, s. 117-131
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Tidskriftsartikel (refereegranskat)abstract
- Computational fluid dynamics (CFD) simulations of large-scale furnaces or reactors for thermal conversion of solid fuels remains challenging partially due to the high computational cost related to the particle sub-models. Owing to the thermally thick nature, it is particularly expensive to simulate the conversion of large fuel particles such as biomass particles. To address this issue, a fast-solving particle model was developed in this work with special attention to the computational efficiency. The model spatially discretizes a fuel particle in one homogenized dimension. The conversion process of the fuel particle is treated as a reactive variable-volume one-dimensional transient heat conduction problem. The model also utilizes several features that are typically found in sharp interphase-based models to reduce the computational cost. Validation of the model was carried out by comparing with experimental results under both pyrolysis and combustion conditions. The accuracy and computational efficiency of the model was thoroughly examined by varying the degrees of temporal and spatial discretization. It was found that the model well predicted pyrolysis and combustion of a single biomass particle within a broad range of temporal and spatial discretization. The time used to simulate the conversion of a biomass particle using the developed model can be more than one order of magnitude smaller than the conversion process itself. It was also revealed that a well-predicted conductive heat transfer inside the particle is essential for a precise simulation of the drying and devolatilization process. The char conversion process, however, is less sensitive to the external heat transfer as it is mainly controlled by the mass diffusion process. Further studies showed that a time step of 1×10−3 s and a spatial discretization of 20 cells were sufficient for simulating the conversion of typical fuel particles in grate-fired and fluidized-bed furnaces. We also demonstrated that when the particle model was implemented in a CFD solver, only 2.2% of computational overhead was introduced by the model. As the model can efficiently employ fixed time stepping, optimal load balancing during parallel computing of many simultaneous conversion processes becomes trivial. This performance opens up new possibilities for treating fuel polydispersity in Eulerian CFD simulations of biomass conversion.
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| 8. |
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| 9. |
- Albinsson, David, 1990, et al.
(författare)
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Copper catalysis at operando conditions - bridging the gap between single nanoparticle probing and catalyst-bed-averaging
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)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.
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| 10. |
- Albinsson, David, 1990, et al.
(författare)
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Operando detection of single nanoparticle activity dynamics inside a model pore catalyst material
- 2020
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Ingår i: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:25
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Tidskriftsartikel (refereegranskat)abstract
- Nanoconfinement in porous catalysts may induce reactant concentration gradients inside the pores due to local conversion. This leads to inefficient active material use since parts of the catalyst may be trapped in an inactive state. Experimentally, these effects remain unstudied due to material complexity and required high spatial resolution. Here, we have nanofabricated quasi-two-dimensional mimics of porous catalysts, which combine the traits of nanofluidics with single particle plasmonics and online mass spectrometry readout. Enabled by single particle resolution at operando conditions during CO oxidation over a Cu model catalyst, we directly visualize reactant concentration gradient formation due to conversion on single Cu nanoparticles inside the “model pore” and how it dynamically controls oxidation state-and, thus, activity-of particles downstream. Our results provide a general framework for single particle catalysis in the gas phase and highlight the importance of single particle approaches for the understanding of complex catalyst materials.
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