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Jakobtorweihen S, Verbeek MG, Lowe CP, Keil FJ, Smit B. Understanding the loading dependence of self-diffusion in carbon nanotubes. PHYSICAL REVIEW LETTERS 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] [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.
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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] [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.
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Heyden A, Peters B, Bell AT, Keil FJ. Comprehensive DFT Study of Nitrous Oxide Decomposition over Fe-ZSM-5. J Phys Chem B 2005. [DOI: 10.1021/jp058049k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Heyden A, Peters B, Bell AT, Keil FJ. Comprehensive DFT Study of Nitrous Oxide Decomposition over Fe-ZSM-5†. J Phys Chem B 2005; 109:1857-73. [PMID: 16851168 DOI: 10.1021/jp040549a] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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.
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Keil FJ, Schreiber D. Rekonstruktion der Porenradienverteilung von porösen Materialien aus Diffusionsmessungen. CHEM-ING-TECH 2004. [DOI: 10.1002/cite.330660212] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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33
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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34
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Swamy KM, Keil FJ. Ultrasonic power measurements in the milliwatt region by the radiation force float method. ULTRASONICS SONOCHEMISTRY 2002; 9:305-310. [PMID: 12404795 DOI: 10.1016/s1350-4177(02)00087-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
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.
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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36
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Hartig F, Keil FJ. Large-scale spherical fixed bed reactors: modeling and optimization. Ind Eng Chem Res 2002. [DOI: 10.1021/ie00015a005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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37
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Luus R, Zhang X, Hartig F, Keil FJ. Use of Piecewise Linear Continuous Optimal Control for Time-Delay Systems. Ind Eng Chem Res 2002. [DOI: 10.1021/ie00038a060] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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38
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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39
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Krishna R, Ellenberger J, Urseanu MI, Keil FJ. Utilisation of bubble resonance phenomena to improve gas-liquid contact. THE SCIENCE OF NATURE - 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] [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.
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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41
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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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. ULTRASONICS SONOCHEMISTRY 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] [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.
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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45
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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46
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Rieckmann C, Keil FJ. Multicomponent Diffusion and Reaction in Three-Dimensional Networks: General Kinetics. Ind Eng Chem Res 1997. [DOI: 10.1021/ie9605847] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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47
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48
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Hinderer J, Keil FJ. Three-dimensional Monte Carlo calculations of diffusion and reaction phenomena in zeolites. Chem Eng Sci 1996. [DOI: 10.1016/0009-2509(96)00134-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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49
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50
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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