1
|
Ekka J, Upadhyay SN, Keil FJ, Pakhira S. Unveiling the role of 2D monolayer Mn-doped MoS 2 material: toward an efficient electrocatalyst for H 2 evolution reaction. Phys Chem Chem Phys 2021; 24:265-280. [PMID: 34881758 DOI: 10.1039/d1cp04344g] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Two-dimensional (2D) monolayer pristine MoS2 transition metal dichalcogenide (TMD) is the most studied material because of its potential applications as nonprecious electrocatalyst for the hydrogen evolution reaction (HER). Previous studies have shown that the basal planes of 2D MoS2 are catalytically inert, and hence it cannot be used directly in desired applications such as electrochemical HER in industry. Here, we thoroughly studied a defect-engineered Mn-doped 2D monolayer MoS2 (Mn-MoS2) material, where Mn was doped in pristine MoS2 to activate its inert basal planes. Using the density functional theory (DFT) method, we performed rigorous inspection of the electronic structures and properties of the 2D monolayer Mn-MoS2 as a promising alternative to noble metal-free catalyst for effective HER. A periodic 2D slab of monolayer Mn-MoS2 was created to study the electronic properties (such as band gap, band structures and total density of states (DOS)) and the reaction pathways occurring on the surface of this material. The detailed HER mechanism was explored by creating an Mn1Mo9S21 non-periodic finite molecular cluster model system using the M06-L DFT method including solvation effects to determine the reaction barriers and kinetics. Our study revealed that the 2D Mn-MoS2 follows the most favorable Volmer-Heyrovsky reaction mechanism with a very low energy barrier during H2 evolution. It was found that the change in the free energy barrier (ΔG) during the H˙-migration (i.e., Volmer) and Heyrovsky reactions is about 10.34-10.79 kcal mol-1 (computed in the solvent phase), indicating that this material is an exceptional electrocatalyst for the HER. The Tafel slope (y) was lower in the case of the 2D monolayer Mn-MoS2 material due to the overlap of the s-orbital of hydrogen and d-orbitals of the Mn atoms in the HOMO and LUMO transition states (TS1 and TS2) of both the Volmer and Heyrovsky reaction steps, respectively. The better stabilization of the atomic orbitals in the HER rate-limiting step Heyrovsky TS2 is the key for reducing the reaction barrier, and thus the overall catalysis, indicating a better electrocatalytic performance for H2 evolution. This study focused on designing low-cost and efficient electrocatalysts for the HER using earth abundant transition metal dichalcogenides (TMDs) and decreasing the activation energy barriers by scrutinizing the kinetics of the reaction to achieve high reactivity.
Collapse
Affiliation(s)
- Joy Ekka
- Department of Physics, Indian Institute of Technology Indore (IIT Indore), Simrol, Khandwa Road, Indore 453552, MP, India.
| | - Shrish Nath Upadhyay
- Department of Metallurgy Engineering and Materials Science (MEMS), Indian Institute of Technology Indore (IIT Indore), Khandwa Road, Simrol, Indore 453552, MP, India
| | - Frerich J Keil
- Department of Chemical Reaction Engineering, Hamburg University of Technology, 21073 Hamburg, Germany
| | - Srimanta Pakhira
- Department of Physics, Indian Institute of Technology Indore (IIT Indore), Simrol, Khandwa Road, Indore 453552, MP, India. .,Department of Metallurgy Engineering and Materials Science (MEMS), Indian Institute of Technology Indore (IIT Indore), Khandwa Road, Simrol, Indore 453552, MP, India.,Centre for Advanced Electronics (CAE), Indian Institute of Technology Indore (IIT Indore), Khandwa Road, Simrol, Indore 453552, MP, India
| |
Collapse
|
2
|
Aranifard S, Bell AT, Keil FJ, Heyden A. Kinetic modeling of nitrous oxide decomposition on Fe-ZSM-5 in the presence of nitric oxide based on parameters obtained from first-principles calculations. Catal Sci Technol 2021. [DOI: 10.1039/d1cy00252j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A variety of experiments for the N2O decomposition over Fe-ZSM-5 catalysts have been simulated in the presence and absence of small amounts of nitric oxide and water vapor.
Collapse
Affiliation(s)
- Sara Aranifard
- Department of Chemical Engineering
- University of South Carolina
- Columbia
- USA
| | - Alexis T. Bell
- Department of Chemical and Biomolecular Engineering
- University of California Berkeley
- Berkeley
- USA
| | - Frerich J. Keil
- Department of Chemical Reaction Engineering
- Hamburg University of Technology
- 21073 Hamburg
- Germany
| | - Andreas Heyden
- Department of Chemical Engineering
- University of South Carolina
- Columbia
- USA
| |
Collapse
|
3
|
Liu X, Zhang Q, Ye G, Li J, Li P, Zhou X, Keil FJ. Deactivation and regeneration of Claus catalyst particles unraveled by pore network model. Chem Eng Sci 2020. [DOI: 10.1016/j.ces.2019.115305] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
4
|
Affiliation(s)
- Guanghua Ye
- State Key Laboratory of Chemical EngineeringEast China University of Science and Technology Shanghai China
| | - Haizhi Wang
- State Key Laboratory of Chemical EngineeringEast China University of Science and Technology Shanghai China
| | - Xinggui Zhou
- State Key Laboratory of Chemical EngineeringEast China University of Science and Technology Shanghai China
| | - Frerich J. Keil
- Institute of Chemical Reaction EngineeringHamburg University of Technology Hamburg Germany
| | | | - Weikang Yuan
- State Key Laboratory of Chemical EngineeringEast China University of Science and Technology Shanghai China
| |
Collapse
|
5
|
Argönül A, Keil FJ. Ethylene Hydrogenation in Pellets with Different Pore Structures, Measured in a One-Sided Single-Pellet Reactor. International Journal of Chemical Reactor Engineering 2019. [DOI: 10.1515/ijcre-2018-0166] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
The ethylene hydrogenation reaction was investigated in a kinetic turbo reactor and a one-sided single-pellet reactor. An empirical kinetic expression was fitted to experimental results taken from the turbo reactor, and the gas compositions at the catalyst centers were measured for three different pore structures by means of the single-pellet reactor. A bimodal pore model was developed and applied to the computation of the gas composition profiles inside the three pore structures. The calculated results were compared to the measurements. A distinct influence of the pore structures on the gas fluxes and concentration profiles inside the pores could be detected which demonstrates that the proper choice of the pellet pore structure is of importance for a high conversion.
Collapse
|
6
|
Abstract
Chemical reactor modelling based on insights and data on a molecular level has become reality over the last few years. Multiscale models describing elementary reaction steps and full microkinetic schemes, pore structures, multicomponent adsorption and diffusion inside pores, and entire reactors have been presented. Quantum mechanical (QM) approaches, molecular simulations (Monte Carlo and molecular dynamics), and continuum equations have been employed for this purpose. Some recent developments in these approaches are presented, in particular time-dependent QM methods, calculation of van der Waals forces, new approaches for force field generation, automatic setup of reaction schemes, and pore modelling. Multiscale simulations are discussed. Applications of these approaches to heterogeneous catalysis are demonstrated for examples that have found growing interest over the last few years, such as metal-support interactions, influence of pore geometry on reactions, noncovalent bonding, reaction dynamics, dynamic changes in catalyst nanoparticle structure, electrocatalysis, solvent effects in catalysis, and multiscale modelling.
Collapse
Affiliation(s)
- Frerich J. Keil
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany
| |
Collapse
|
7
|
Abstract
Abstract
Process intensification (PI) is a rapidly growing field of research and industrial development that has already created many innovations in chemical process industry. PI is directed toward substantially smaller, cleaner, more energy-efficient technology. Furthermore, PI aims at safer and sustainable technological developments. Its tools are reduction of the number of devices (integration of several functionalities in one apparatus), improving heat and mass transfer by advanced mixing technologies and shorter diffusion pathways, miniaturization, novel energy techniques, new separation approaches, integrated optimization and control strategies. This review discusses many of the recent developments in PI. Starting from fundamental definitions, microfluidic technology, mixing, modern distillation techniques, membrane separation, continuous chromatography, and application of gravitational, electric, and magnetic fields will be described.
Collapse
Affiliation(s)
- Frerich J. Keil
- Institute of Chemical Reaction Engineering , Hamburg University of Technology , 21073 Hamburg , Germany
| |
Collapse
|
8
|
Hovestadt M, Bendt S, Mondal SS, Behrens K, Reif F, Döpken M, Holdt HJ, Keil FJ, Hartmann M. Experimental and Theoretical Analysis of the Influence of Different Linker Molecules in Imidazolate Frameworks Potsdam (IFP-n) on the Separation of Olefin-Paraffin Mixtures. Langmuir 2017; 33:11170-11179. [PMID: 28793757 DOI: 10.1021/acs.langmuir.7b02016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Four metal-organic frameworks with similar topology but different chemical environment inside the pore structure, namely, IFP-1, IFP-3, IFP-5, and IFP-7, have been investigated with respect to the separation potential for olefin-paraffin mixtures as well as the influence of the different linkers on adsorption properties using experiments and Monte Carlo simulations. All IFP structures show a higher adsorption of ethane compared to ethene with the exception of IFP-7 which shows no selectivity in breakthrough experiments. For propane/propane separation, all adsorbents show a higher adsorption for the olefin. The experimental results agree quite well with the simulated values except for the IFP-7, which is presumably due to the flexibility of the structure. Moreover, the experimental and simulated isotherms were confirmed with breakthrough experiments that render IFP-1, IFP-3, and IFP-5 as suitable for the purification of ethene from ethane.
Collapse
Affiliation(s)
- Maximilian Hovestadt
- Erlangen Catalysis Resource Center (ECRC), Friedrich-Alexander-Universität Erlangen-Nürnberg , Egerlandstraße 3, 91058 Erlangen, Germany
| | - Stephan Bendt
- Institute of Chemical Reaction Engineering, Hamburg University of Technology , Eissendorferstraße 38, 21073 Hamburg, Germany
| | - Suvendu Sekhar Mondal
- Institute for Inorganic Chemistry, University of Potsdam , Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany
| | - Karsten Behrens
- Institute for Inorganic Chemistry, University of Potsdam , Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany
| | - Florian Reif
- Erlangen Catalysis Resource Center (ECRC), Friedrich-Alexander-Universität Erlangen-Nürnberg , Egerlandstraße 3, 91058 Erlangen, Germany
| | - Merle Döpken
- Institute of Chemical Reaction Engineering, Hamburg University of Technology , Eissendorferstraße 38, 21073 Hamburg, Germany
| | - Hans-Jürgen Holdt
- Institute for Inorganic Chemistry, University of Potsdam , Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany
| | - Frerich J Keil
- Institute of Chemical Reaction Engineering, Hamburg University of Technology , Eissendorferstraße 38, 21073 Hamburg, Germany
| | - Martin Hartmann
- Erlangen Catalysis Resource Center (ECRC), Friedrich-Alexander-Universität Erlangen-Nürnberg , Egerlandstraße 3, 91058 Erlangen, Germany
| |
Collapse
|
9
|
Titze T, Lauerer A, Heinke L, Chmelik C, Zimmermann NER, Keil FJ, Ruthven DM, Kärger J. Transport in Nanoporous Materials Including MOFs: The Applicability of Fick’s Laws. Angew Chem Int Ed Engl 2015; 54:14580-3. [DOI: 10.1002/anie.201506954] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Tobias Titze
- Department of Interface Physics, University of Leipzig, Linnéstrasse 5, 04103 Leipzig (Germany)
| | - Alexander Lauerer
- Department of Interface Physics, University of Leipzig, Linnéstrasse 5, 04103 Leipzig (Germany)
| | - Lars Heinke
- Institute of Functional Interfaces, Karlsruher Institut für Technologie, Karlsruhe (Germany)
| | - Christian Chmelik
- Department of Interface Physics, University of Leipzig, Linnéstrasse 5, 04103 Leipzig (Germany)
| | - Nils E. R. Zimmermann
- Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, (USA)
| | - Frerich J. Keil
- Department of Chemical Reaction Engineering, Hamburg University of Technology, Hamburg (Germany)
| | | | - Jörg Kärger
- Department of Interface Physics, University of Leipzig, Linnéstrasse 5, 04103 Leipzig (Germany)
| |
Collapse
|
10
|
Titze T, Lauerer A, Heinke L, Chmelik C, Zimmermann NER, Keil FJ, Ruthven DM, Kärger J. Transport in nanoporösen Materialien, einschließlich MOFs: über die Anwendbarkeit der Fickschen Gesetze. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201506954] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
|
11
|
Affiliation(s)
- Frerich J Keil
- Department of Chemical Engineering, Technical University Hamburg Harburg, Schwarzenbergstr. 95 21073 Hamburg, Germany.
| |
Collapse
|
12
|
Liang J, Fieg G, Keil FJ, Jakobtorweihen S. Adsorption of Proteins onto Ion-Exchange Chromatographic Media: A Molecular Dynamics Study. Ind Eng Chem Res 2012. [DOI: 10.1021/ie301407b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Juan Liang
- Institute of Process and Plant Engineering and ‡Institute of
Chemical Reaction Engineering, Hamburg University of Technology, 21073 Hamburg, Germany
| | - Georg Fieg
- Institute of Process and Plant Engineering and ‡Institute of
Chemical Reaction Engineering, Hamburg University of Technology, 21073 Hamburg, Germany
| | - Frerich J. Keil
- Institute of Process and Plant Engineering and ‡Institute of
Chemical Reaction Engineering, Hamburg University of Technology, 21073 Hamburg, Germany
| | - Sven Jakobtorweihen
- Institute of Process and Plant Engineering and ‡Institute of
Chemical Reaction Engineering, Hamburg University of Technology, 21073 Hamburg, Germany
| |
Collapse
|
13
|
|
14
|
Zimmermann NE, Haranczyk M, Sharma M, Liu B, Smit B, Keil FJ. Adsorption and diffusion in zeolites: the pitfall of isotypic crystal structures. Molecular Simulation 2011. [DOI: 10.1080/08927022.2011.562502] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
15
|
Hansen N, Kerber T, Sauer J, Bell AT, Keil FJ. Quantum Chemical Modeling of Benzene Ethylation over H-ZSM-5 Approaching Chemical Accuracy: A Hybrid MP2:DFT Study. J Am Chem Soc 2010; 132:11525-38. [DOI: 10.1021/ja102261m] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Niels Hansen
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany, Institut für Chemie, Humboldt-Universität zu Berlin, D-10099 Berlin, Germany, and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462
| | - Torsten Kerber
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany, Institut für Chemie, Humboldt-Universität zu Berlin, D-10099 Berlin, Germany, and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462
| | - Joachim Sauer
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany, Institut für Chemie, Humboldt-Universität zu Berlin, D-10099 Berlin, Germany, and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462
| | - Alexis T. Bell
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany, Institut für Chemie, Humboldt-Universität zu Berlin, D-10099 Berlin, Germany, and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462
| | - Frerich J. Keil
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany, Institut für Chemie, Humboldt-Universität zu Berlin, D-10099 Berlin, Germany, and Department of Chemical Engineering, University of California, Berkeley, California 94720-1462
| |
Collapse
|
16
|
|
17
|
Wilke K, Wick K, Keil FJ, Wittern KP, Wepf R, Biel SS. A strategy for correlative microscopy of large skin samples: towards a holistic view of axillary skin complexity. Exp Dermatol 2007; 17:73-81. [PMID: 18005049 DOI: 10.1111/j.1600-0625.2007.00635.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Knowledge about the structural elements of skin and its appendices is an essential prerequisite for understanding their complex functions and interactions. The hence necessary morphological description across several orders of scale not only requires the investigation at the light microscopic level but also ultrastructural investigation, ideally on the identical sample. For a correlative and multimodal observation one unique preparation protocol is mandatory. As a compromise between sample sizes of >500 microm in diameter on the one hand and optimal preservation of antigenicity and morphology on the other, we developed a new preparation protocol that allows (i) 3D reconstruction of the resin-embedded sample by confocal light microscopy prior to (ii) direct immunolocalization of target proteins within selected sample planes by light and fluorescence microscopy or transmission electron microscopy. Alternatively, (iii) serial cryosections of the frozen sample can be taken for characterizing the sample in toto. With this unique approach we were able to fully demonstrate the structural complexity of axillary skin samples, increasing the structural resolution from 3D reconstruction of the whole gland up to ultrastructural investigations at the subcellular level. We could demonstrate that axillary sweat glands are not separately distributed, as has been assumed to date; instead, they seem to be intricately twisted into one another. This promotes the concept of a complex axillary sweat gland organ instead of single sweat gland entities.
Collapse
|
18
|
Jakobtorweihen S, Lowe CP, Keil FJ, Smit B. Diffusion of chain molecules and mixtures in carbon nanotubes: The effect of host lattice flexibility and theory of diffusion in the Knudsen regime. J Chem Phys 2007; 127:024904. [PMID: 17640148 DOI: 10.1063/1.2753477] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
A novel algorithm for modeling the influence of the host lattice flexibility in molecular dynamics simulations is extended to chain-like molecules and mixtures. This technique, based on a Lowe-Andersen thermostat, maintains the advantages of both simplicity and efficiency. The same diffusivities and other properties of the flexible framework system are reproduced. Advantageously, the computationally demanding flexible host lattice simulations can be avoided. Using this methodology we study the influence of flexibility on diffusion of n-alkanes inside single-walled carbon nanotubes. Furthermore, results are shown for diffusion of two mixtures (methane-helium and ethane-butane). Using these results we investigate the accuracy of theories describing diffusion in the Knudsen regime. For the dynamics in carbon nanotubes the Knudsen diffusivities are much too low. The Smoluchowski model gives better results. Interestingly, the extended Smoluchowski model can reproduce our simulation results obtained with a rigid host lattice. We modify this model to also treat collisions with a flexible interface correctly. As the tangential momentum accommodation coefficient is needed for the theoretical models, we introduce a simple concept to calculate it.
Collapse
Affiliation(s)
- S Jakobtorweihen
- Department of Chemical Reaction Engineering, Hamburg University of Technology, Eissendorfer Strasse 38, D-21073 Hamburg, Germany.
| | | | | | | |
Collapse
|
19
|
Heyden A, Bell AT, Keil FJ. Efficient methods for finding transition states in chemical reactions: comparison of improved dimer method and partitioned rational function optimization method. J Chem Phys 2007; 123:224101. [PMID: 16375464 DOI: 10.1063/1.2104507] [Citation(s) in RCA: 415] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A combination of interpolation methods and local saddle-point search algorithms is probably the most efficient way of finding transition states in chemical reactions. Interpolation methods such as the growing-string method and the nudged-elastic band are able to find an approximation to the minimum-energy pathway and thereby provide a good initial guess for a transition state and imaginary mode connecting both reactant and product states. Since interpolation methods employ usually just a small number of configurations and converge slowly close to the minimum-energy pathway, local methods such as partitioned rational function optimization methods using either exact or approximate Hessians or minimum-mode-following methods such as the dimer or the Lanczos method have to be used to converge to the transition state. A modification to the original dimer method proposed by [Henkelman and Jonnson J. Chem. Phys. 111, 7010 (1999)] is presented, reducing the number of gradient calculations per cycle from six to four gradients or three gradients and one energy, and significantly improves the overall performance of the algorithm on quantum-chemical potential-energy surfaces, where forces are subject to numerical noise. A comparison is made between the dimer methods and the well-established partitioned rational function optimization methods for finding transition states after the use of interpolation methods. Results for 24 different small- to medium-sized chemical reactions covering a wide range of structural types demonstrate that the improved dimer method is an efficient alternative saddle-point search algorithm on medium-sized to large systems and is often even able to find transition states when partitioned rational function optimization methods fail to converge.
Collapse
Affiliation(s)
- Andreas Heyden
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany.
| | | | | |
Collapse
|
20
|
Jakobtorweihen S, Hansen N, Keil FJ. Combining reactive and configurational-bias Monte Carlo: confinement influence on the propene metathesis reaction system in various zeolites. J Chem Phys 2007; 125:224709. [PMID: 17176156 DOI: 10.1063/1.2404658] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In order to efficiently calculate chemical equilibria of large molecules in a confined environment the reactive Monte Carlo technique is combined with the configurational-bias Monte Carlo approach. To prove that detailed balance is fulfilled the acceptance rule for this combination of particular Monte Carlo techniques is derived in detail. Notably, by using this derivation all other acceptance rules of any Monte Carlo trial moves usually carried out in combination with the configurational-bias Monte Carlo approach can be deduced from it. As an application of the combination of reactive and configurational-bias Monte Carlo the influence of different zeolitic confinements (MFI, TON, LTL, and FER) on the reaction equilibrium and the selectivity of the propene metathesis reaction system was investigated. Compared to the bulk phase the conversion is increased significantly. The authors study this reaction system in the temperature range between 300 and 600 K, and the pressure range from 1 to 7 bars. In contrast to the bulk phase, pressure and temperature have a strong influence on the composition of the reaction mixture in confinement. At low pressures and temperatures both conversion and selectivity are highest. Furthermore, the equilibrium composition is strongly dependent on the type of zeolite. This demonstrates the important role of the host structure in catalytic systems.
Collapse
Affiliation(s)
- S Jakobtorweihen
- Chemical Reaction Engineering, Hamburg University of Technology, Eissendorfer Strasse 38, D-21073 Hamburg, Germany.
| | | | | |
Collapse
|
21
|
Heyden A, Hansen N, Bell AT, Keil FJ. Nitrous Oxide Decomposition over Fe-ZSM-5 in the Presence of Nitric Oxide: A Comprehensive DFT Study. J Phys Chem B 2006; 110:17096-114. [PMID: 16928005 DOI: 10.1021/jp062814t] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A number of experimental studies have shown recently that ppm-level additions of nitric oxide (NO) enhance the rate of nitrous oxide (N(2)O) decomposition catalyzed by Fe-ZSM-5 at low temperatures. In the present work, the NO-assisted N(2)O decomposition over mononuclear iron sites in Fe-ZSM-5 was studied on a molecular level using density functional theory (DFT) and transition-state theory. A reaction network consisting of over 100 elementary reactions was considered. The structure and energies of potential-energy minima were determined for all stable species, as were the structures and energies of all transition states. Reactions involving changes in spin potential-energy surfaces were also taken into account. In the absence of NO and at temperatures below 690 K, most active single iron sites (Z(-)[FeO](+)) are poisoned by small concentrations of water in the gas phase; however, in the presence of NO, these poisoned sites are converted into a novel active iron center (Z(-)[FeOH](+)). These latter sites are capable of promoting the dissociation of N(2)O into a surface oxygen atom and gas-phase N(2). The surface oxygen atom is removed by reaction with NO or nitrogen dioxide (NO(2)). N(2)O dissociation is the rate-limiting step in the reaction mechanism. At higher temperatures, water desorbs from inactive iron sites and the reaction mechanism for N(2)O decomposition becomes independent of NO, reverting to the reaction mechanism previously reported by Heyden et al. [J. Phys. Chem. B 2005, 109, 1857].
Collapse
Affiliation(s)
- Andreas Heyden
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany.
| | | | | | | |
Collapse
|
22
|
Abstract
We study the self-diffusion of simple gases inside single-walled carbon nanotubes at the zero-loading limit by molecular dynamics simulations. The host-framework flexibility influence is taken into account. In particular, we study the influences of nanotube size and temperature. For the carbon-nanotube radius-dependent self-diffusivities, a maximum is observed, which resembles the so-called levitation effect. This occurs for pores having a radius comparable to the position of the interaction-energy minimum. Surprisingly, the temperature influence is not uniform throughout different pore sizes. Diffusivities are expected to increase with temperature. This effect is observed for carbon nanotubes distinctly larger than the guest molecules. Remarkably, for smaller pores, the self-diffusivities decrease with increasing temperature or exhibit a maximum in the temperature dependence. This effect is caused by competing influences of collision frequency and temperature.
Collapse
Affiliation(s)
- S Jakobtorweihen
- Chemical Reaction Engineering, Hamburg University of Technology, Eissendorfer Str. 38, D-21073 Hamburg, Germany.
| | | | | |
Collapse
|
23
|
Jakobtorweihen S, Lowe CP, Keil FJ, Smit B. A novel algorithm to model the influence of host lattice flexibility in molecular dynamics simulations: Loading dependence of self-diffusion in carbon nanotubes. J Chem Phys 2006; 124:154706. [PMID: 16674250 DOI: 10.1063/1.2185619] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
We describe a novel algorithm that includes the effect of host lattice flexibility into molecular dynamics simulations that use rigid lattices. It uses a Lowe-Andersen thermostat for interface-fluid collisions to take the most important aspects of flexibility into account. The same diffusivities and other properties of the flexible framework system are reproduced at a small fraction of the computational cost of an explicit simulation. We study the influence of flexibility on the self-diffusion of simple gases inside single walled carbon nanotubes. Results are shown for different guest molecules (methane, helium, and sulfur hexafluoride), temperatures, and types of carbon nanotubes. We show, surprisingly, that at low loadings flexibility is always relevant. Notably, it has a crucial influence on the diffusive dynamics of the guest molecules.
Collapse
Affiliation(s)
- S Jakobtorweihen
- Chemical Reaction Engineering, Hamburg University of Technology, Eissendorfer Strasse 38, D-21073 Hamburg, Germany.
| | | | | | | |
Collapse
|
24
|
Shao Y, Molnar LF, Jung Y, Kussmann J, Ochsenfeld C, Brown ST, Gilbert ATB, Slipchenko LV, Levchenko SV, O'Neill DP, DiStasio RA, Lochan RC, Wang T, Beran GJO, Besley NA, Herbert JM, Lin CY, Van Voorhis T, Chien SH, Sodt A, Steele RP, Rassolov VA, Maslen PE, Korambath PP, Adamson RD, Austin B, Baker J, Byrd EFC, Dachsel H, Doerksen RJ, Dreuw A, Dunietz BD, Dutoi AD, Furlani TR, Gwaltney SR, Heyden A, Hirata S, Hsu CP, Kedziora G, Khalliulin RZ, Klunzinger P, Lee AM, Lee MS, Liang W, Lotan I, Nair N, Peters B, Proynov EI, Pieniazek PA, Rhee YM, Ritchie J, Rosta E, Sherrill CD, Simmonett AC, Subotnik JE, Woodcock HL, Zhang W, Bell AT, Chakraborty AK, Chipman DM, Keil FJ, Warshel A, Hehre WJ, Schaefer HF, Kong J, Krylov AI, Gill PMW, Head-Gordon M. Advances in methods and algorithms in a modern quantum chemistry program package. Phys Chem Chem Phys 2006; 8:3172-91. [PMID: 16902710 DOI: 10.1039/b517914a] [Citation(s) in RCA: 2118] [Impact Index Per Article: 117.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.
Collapse
Affiliation(s)
- Yihan Shao
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
25
|
Wilke K, Wepf R, Keil FJ, Wittern KP, Wenck H, Biel SS. Are Sweat Glands an Alternate Penetration Pathway? Understanding the Morphological Complexity of the Axillary Sweat Gland Apparatus. Skin Pharmacol Physiol 2005; 19:38-49. [PMID: 16247248 DOI: 10.1159/000089142] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 07/21/2005] [Indexed: 12/20/2022]
Abstract
To build an effective barrier against the penetration of extrinsic agents is one of the skin's main functions. The barrier properties of the stratum corneum and the epidermis have been subject to extensive studies in the past while the role of skin appendages as possible pathways of penetration are only rarely described. In order to study the possible penetration barriers in these complex appendages, a careful investigation of their morphology and ultrastructure has to be done. Studying the morphology of axillary skin appendages requires clear-cut criteria for the differentiation between eccrine, apocrine and apoeccrine glands. Therefore we studied the distribution of proteins described to be specific for either eccrine or apocrine glands (CD15, CD44, S-100 and milk fat globulin) on axillary skin samples from healthy young adults by immunofluorescence. Additionally, we examined the distribution of cytoskeletal proteins such as cytokeratins (1/10/11, 14, 18) and F-actin. For a more detailed understanding of the possible versatile barrier elements of the axillary sweat glands, we studied the distribution of tight-junction-associated proteins (occludin, claudin 1, claudin 4). The coils and the dermal duct may provide an active barrier built of tight junctions as occludin and claudin 4 are co-localized. However, the intra-epidermal duct did not show any co-localization of the investigated proteins. By combining morphological features as revealed by F-actin staining and the distribution of the above-mentioned proteins, immunocytochemical typing of eccrine and apocrine glands becomes possible. With this tool, we could also confirm the existence of apoeccrine glands and locate them in their 'natural environment'.
Collapse
Affiliation(s)
- K Wilke
- Beiersdorf AG, Hamburg, Deutschland
| | | | | | | | | | | |
Collapse
|
26
|
Jakobtorweihen S, Verbeek MG, Lowe CP, Keil FJ, Smit B. Understanding the loading dependence of self-diffusion in carbon nanotubes. Phys Rev Lett 2005; 95:044501. [PMID: 16090813 DOI: 10.1103/physrevlett.95.044501] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2005] [Indexed: 05/03/2023]
Abstract
The influence of flexible walls on the self-diffusion of CH4 in an isolated single walled carbon nanotube, as an example, is studied by molecular dynamics simulations. By simulating the carbon nanotube as a flexible framework we demonstrate that the flexibility has a crucial influence on self-diffusion at low loadings. We show how this influence can be incorporated in a simulation of a rigid nanotube by using a Lowe-Andersen thermostat which works on interface-fluid collisions. The reproduction of the results of a flexible carbon nanotube by a rigid nanotube simulation is excellent.
Collapse
Affiliation(s)
- S Jakobtorweihen
- Chemical Reaction Engineering, Hamburg University of Technology, Germany
| | | | | | | | | |
Collapse
|
27
|
Hansen N, Jakobtorweihen S, Keil FJ. Reactive Monte Carlo and grand-canonical Monte Carlo simulations of the propene metathesis reaction system. J Chem Phys 2005; 122:164705. [PMID: 15945697 DOI: 10.1063/1.1884108] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The influence of silicalite-1 pores on the reaction equilibria and the selectivity of the propene metathesis reaction system in the temperature range between 300 and 600 K and the pressure range from 0.5 to 7 bars has been investigated with molecular simulations. The reactive Monte Carlo (RxMC) technique was applied for bulk-phase simulations in the isobaric-isothermal ensemble and for two phase systems in the Gibbs ensemble. Additionally, Monte Carlo simulations in the grand-canonical ensemble (GCMC) have been carried out with and without using the RxMC technique. The various simulation procedures were combined with the configurational-bias Monte Carlo approach. It was found that the GCMC simulations are superior to the Gibbs ensemble simulations for reactions where the bulk-phase equilibrium can be calculated in advance and does not have to be simulated simultaneously with the molecules inside the pore. The confined environment can increase the conversion significantly. A large change in selectivity between the bulk phase and the pore phase is observed. Pressure and temperature have strong influences on both conversion and selectivity. At low pressure and temperature both conversion and selectivity have the highest values. The effect of confinement decreases as the temperature increases.
Collapse
Affiliation(s)
- Niels Hansen
- Hamburg University of Technology, Chemical Reaction Engineering, Eissendorfer Strasse 38, D-21073 Hamburg, Germany.
| | | | | |
Collapse
|
28
|
|
29
|
|
30
|
Abstract
The reaction mechanism for nitrous oxide decomposition has been studied on hydrated and dehydrated mononuclear iron sites in Fe-ZSM-5 using density functional theory. In total, 46 different surface species with different spin states (spin multiplicity M(S) = 4 or 6) and 63 elementary reactions were considered. Heats of adsorption, activation barriers, reaction rates, and minimum energy pathways were determined. The approximate minimum energy pathways and transition states were calculated using the "growing string method" and a modified "dimer method". Spin surface crossing (e.g., O(2) desorption) was considered. The minimum potential energy structure on the seam of two potential energy surfaces was determined with a multiplier penalty function algorithm by Powell and approximate rates of spin surface crossings were calculated. It was found that nitrous oxide decomposition is first order with respect to nitrous oxide concentration and zero order with respect to oxygen concentration. Water impurities in the gas stream have a strong inhibiting effect. In the concentration range of 1-100 ppb, the presence of water vapor influences the surface composition and the apparent rate coefficient. This is especially relevant in the temperature range of 600-700 K where most experimental kinetic studies are performed. Apparent activation barriers determined over this temperature range vary from 28.4 (1 ppb H(2)O) to 54.8 kcal/mol (100 ppb H(2)O). These results give an explanation why different research groups and different catalyst pretreatments often result in very different activation barriers and preexponential factors. Altogether perfect agreement with experimental results could be achieved.
Collapse
Affiliation(s)
- Andreas Heyden
- Department of Chemical Engineering, Hamburg University of Technology, D-21073 Hamburg, Germany.
| | | | | | | |
Collapse
|
31
|
|
32
|
|
33
|
Düren T, Jakobtorweihen S, Keil FJ, Seaton NA. Grand canonical molecular dynamics simulations of transport diffusion in geometrically heterogeneous pores. Phys Chem Chem Phys 2003. [DOI: 10.1039/b207843k] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
34
|
Abstract
The radiation force float technique is extended in the present investigation, for the determination of the total radiated low ultrasonic power in the milliwatt region. It is elucidated, experimentally, using floats having a conical reflecting target comprising of new material (teflon insulated copper wire) stems with smaller diameters (0.55 and 1 mm). The sensitivity is improved with these two stems and the ultrasonic power levels are measured in the range from 1.4 to 140 mW and 4.6 to 460 mW respectively and the results are reproducible within +/- 5%. Limitations of float technique and factors influencing the uncertainties involved for the high quality ultrasonic power measurements are discussed. The proposed method is simple, versatile and inexpensive and can be used as an interim standard.
Collapse
Affiliation(s)
- K M Swamy
- Regional Research Laboratory, Bhubaneswar 751 013, India.
| | | |
Collapse
|
35
|
Heyden A, Düren T, J. Keil F. Study of molecular shape and non-ideality effects on mixture adsorption isotherms of small molecules in carbon nanotubes: A grand canonical Monte Carlo simulation study. Chem Eng Sci 2002. [DOI: 10.1016/s0009-2509(02)00131-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
36
|
|
37
|
|
38
|
Poplawski K, Lichtenberger J, Keil FJ, Schnitzlein K, Amiridis MD. Catalytic oxidation of 1,2-dichlorobenzene over ABO3-type perovskites. Catal Today 2000. [DOI: 10.1016/s0920-5861(00)00434-x] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
39
|
Krishna R, Ellenberger J, Urseanu MI, Keil FJ. Utilisation of bubble resonance phenomena to improve gas-liquid contact. Naturwissenschaften 2000; 87:455-9. [PMID: 11129945 DOI: 10.1007/s001140050758] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In several branches of science and technology a gaseous phase is dispersed into a liquid in the form of bubbles, a gaseous component then dissolves into the liquid and subsequently undergoes chemical reaction. The overall process performance can be improved substantially when the area of gas-liquid contact is increased. By subjecting the liquid phase to low frequency vibrations, the bubbles are shown to suffer significant breakage, induced by resonance. When the vibration is properly tuned, the interfacial area is found to increase by a factor of 1.8-2.4, depending on the properties of the liquid. Resonance-induced bubble breakage phenomena have a great potential for improving the rates of chemical processes involving fast reactions, with minimal energy input.
Collapse
Affiliation(s)
- R Krishna
- Department of Chemical Engineering, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
| | | | | | | |
Collapse
|
40
|
Düren T, Keil FJ. Molekulare Simulation von Adsorptionsvorgängen in Kohlenstoff-Nanoröhrchen. CHEM-ING-TECH 2000. [DOI: 10.1002/1522-2640(200008)72:8<833::aid-cite833>3.0.co;2-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
41
|
|
42
|
Dähnke SW, Keil FJ. Modeling of linear pressure fields in sonochemical reactors considering an inhomogeneous density distribution of cavitation bubbles. Chem Eng Sci 1999. [DOI: 10.1016/s0009-2509(98)00340-6] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
43
|
Dähnke S, Swamy KM, Keil FJ. Modeling of three-dimensional pressure fields in sonochemical reactors with an inhomogeneous density distribution of cavitation bubbles. Comparison of theoretical and experimental results. Ultrason Sonochem 1999; 6:31-41. [PMID: 11233936 DOI: 10.1016/s1350-4177(98)00026-1] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
During the last 50 years extensive experimental investigation has been carried out on the chemical effects of ultrasound, but limited work has been reported on modeling. This paper presents a new model in which a numerical calculation of the three-dimensional linear sound pressure field distribution in a commonly used sonoreactor containing three transducers is carried out. In this model the inhomogeneous three-dimensional time-dependent wave equation was solved using the finite difference approach. The modeled results are then compared with the experimentally measured values, and the agreement, in general, is found to be good. Further, our modeling studies have an advantage, since they clearly describe the continuous sound pressure field structure, unlike previously reported results in which some information is missing due to limited intermittent measured points.
Collapse
Affiliation(s)
- S Dähnke
- Technical University of Hamburg-Harburg, Hamburg, Germany
| | | | | |
Collapse
|
44
|
Fergg F, Keil FJ. Molecular dynamics calculations and Monte Carlo simulation of diffusivities in aqueous systems application to nitrate reduction on bimetal catalyst immobilized in poly (vinyl alcohol)-hydrogel. Comput Chem Eng 1998. [DOI: 10.1016/s0098-1354(98)00107-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
45
|
Dähnke S, Keil FJ. Modeling of Three-Dimensional Linear Pressure Fields in Sonochemical Reactors with Homogeneous and Inhomogeneous Density Distributions of Cavitation Bubbles. Ind Eng Chem Res 1998. [DOI: 10.1021/ie9703393] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sascha Dähnke
- Department of Chemical Engineering, Technical University of HamburgHarburg, Eissendorfer Strasse 38, D-21071 Hamburg, Germany
| | - Frerich J. Keil
- Department of Chemical Engineering, Technical University of HamburgHarburg, Eissendorfer Strasse 38, D-21071 Hamburg, Germany
| |
Collapse
|
46
|
Affiliation(s)
- Christina Rieckmann
- Department of Chemical Engineering, Technical University of Hamburg−Harburg, Eissendorfer Strasse 38, D-21073 Hamburg, Germany
| | - Frerich J. Keil
- Department of Chemical Engineering, Technical University of Hamburg−Harburg, Eissendorfer Strasse 38, D-21073 Hamburg, Germany
| |
Collapse
|
47
|
|
48
|
|
49
|
|
50
|
Schoenfelder H, Hinderer J, Werther J, Keil FJ. Methanol to olefins—prediction of the performance of a circulating fluidized-bed reactor on the basis of kinetic experiments in a fixed-bed reactor. Chem Eng Sci 1994. [DOI: 10.1016/0009-2509(94)00332-7] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|