Academic literature on the topic 'Langmuir-Hinshelwood'
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Journal articles on the topic "Langmuir-Hinshelwood"
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Eiswirth, M., J. Bürger, P. Strasser, and G. Ertl. "Oscillating Langmuir−Hinshelwood Mechanisms." Journal of Physical Chemistry 100, no. 49 (January 1996): 19118–23. http://dx.doi.org/10.1021/jp961688y.
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Kumar, K. Vasanth, K. Porkodi, and F. Rocha. "Langmuir–Hinshelwood kinetics – A theoretical study." Catalysis Communications 9, no. 1 (January 2008): 82–84. http://dx.doi.org/10.1016/j.catcom.2007.05.019.
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Overman, A. R., and R. V. Scholtz. "Langmuir‐hinshelwood model of soil phosphorus kinetics." Communications in Soil Science and Plant Analysis 30, no. 1-2 (January 1999): 109–19. http://dx.doi.org/10.1080/00103629909370188.
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Kang, H. C., and W. H. Weinberg. "Structure of a Langmuir-Hinshelwood reaction interface." Physical Review E 48, no. 5 (November 1, 1993): 3464–69. http://dx.doi.org/10.1103/physreve.48.3464.
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WANG, Dezheng. "Experimental Conditions for Valid Langmuir-Hinshelwood Kinetics." Chinese Journal of Catalysis 31, no. 8 (August 2010): 972–78. http://dx.doi.org/10.1016/s1872-2067(10)60103-9.
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Alvarez-Ramirez, J., R. Femat, M. Meraz, and C. Ibarra-Valdez. "Some remarks on the Langmuir–Hinshelwood kinetics." Journal of Mathematical Chemistry 54, no. 2 (October 15, 2015): 375–92. http://dx.doi.org/10.1007/s10910-015-0566-7.
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HO, T. "Collective behavior of many langmuir-hinshelwood reactions." Journal of Catalysis 129, no. 2 (June 1991): 524–29. http://dx.doi.org/10.1016/0021-9517(91)90055-9.
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Maganti, Lasya, Madhuri Jash, Anju Nair, and T. P. Radhakrishnan. "Nanoparticle assembly following Langmuir–Hinshelwood kinetics on a Langmuir film and chain networks captured in LB films." Physical Chemistry Chemical Physics 17, no. 11 (2015): 7386–94. http://dx.doi.org/10.1039/c5cp00606f.
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Negatively charged metal nanoparticles assemble as chain networks through Langmuir–Hinshelwood kinetics on a Langmuir film of positively charged amphiphiles. The extension of the networks captured in Langmuir–Blodgett films is tuned by the deposition pressure.
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Uskov, Sergey I., Dmitriy I. Potemkin, Leniza V. Enikeeva, Pavel V. Snytnikov, Irek M. Gubaydullin, and Vladimir A. Sobyanin. "Propane Pre-Reforming into Methane-Rich Gas over Ni Catalyst: Experiment and Kinetics Elucidation via Genetic Algorithm." Energies 13, no. 13 (July 2, 2020): 3393. http://dx.doi.org/10.3390/en13133393.
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Pre-reforming of propane was studied over an industrial nickel-chromium catalyst under pressures of 1 and 5 bar, at a low steam to carbon molar ratio of 1, in the temperature range of 220–380 °C and at flow rates of 4000 and 12,000 h−1. It was shown that propane conversion proceeded more efficiently at low pressure (1 atm) and temperatures above 350 °C. A genetic algorithm was applied to search for kinetic parameters better fitting experimental results in such a wide range of experimental conditions. Power law and Langmuir–Hinshelwood kinetics were considered. It was shown that only Langmuir–Hinshelwood type kinetics correctly described the experimental data and could be used to simulate the process of propane pre-reforming and predict propane conversion under the given reaction conditions. The significance of Langmuir–Hinshelwood kinetics increases under high pressure and temperatures below 350 °C.
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Borovinskaya, Ekaterina. "Redundancy-Free Models for Mathematical Descriptions of Three-Phase Catalytic Hydrogenation of Cinnamaldehyde." Catalysts 11, no. 2 (February 4, 2021): 207. http://dx.doi.org/10.3390/catal11020207.
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A new approach on how to formulate redundancy-free models for mathematical descriptions of three-phase catalytic hydrogenation of cinnamaldehyde is presented. An automatically created redundant (generalized) model is formulated according to the complete reaction network. Models based on formal kinetics and kinetics concerning the Langmuir-Hinshelwood theory for three-phase catalytic hydrogenation of cinnamaldehyde were investigated. Redundancy-free models were obtained as a result of a step-by-step elimination of model parameters using sensitivity and interval analysis. Starting with 24 parameters in the redundant model, the redundancy-free model based on the Langmuir-Hinshelwood mechanism contains 6 parameters, while the model based on formal kinetics includes only 4 parameters. Due to less degrees of freedom of molecular rotation in the adsorbed state, the probability of a direct conversion of cinnamaldehyde to 3-phenylpropanol according to the redundancy-free model based on Langmuir-Hinshelwood approach is practically negligible compared to the model based on formal kinetics.
Dissertations / Theses on the topic "Langmuir-Hinshelwood"
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Petzer, Adéle. "Kinetics of the photocatalytic reduction of platinum (IV) in a batch and flow reactor / Adéle Petzer." Thesis, North-West University, 2012. http://hdl.handle.net/10394/7612.
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Semiconductor photocatalysis has received considerable attention in recent years as
an alternative for treating water polluted with hazardous organic chemicals. The
process, as a means of removal of persistent water contaminants such as pesticides,
which exhibit chemical stability and resistance to biodegradation, has attracted the
attention of many researchers. To a lesser extent, it has also been studied for
decontamination of water containing toxic metals.
Precious and common metals enter waters through washing, rinsing, pickling and
surface treatment procedures of industrial processes, such as hydrometallurgy,
plating and photography. As a result we are living in an environment with a multitude
of potentially harmful toxic metal ions. In contrast, the demand for metals increases
significantly with the development and growth of industry.
Even though research on the photocatalytic recovery of waste and noble metals has
escalated in the past 10 years, the practical implementation of these processes is not
yet justified. The successful implementation of large scale reactors, for industrial
application, has to consider several reactor design parameters that must be
optimised, such as reactor geometry and the utilization of radiated energy.
In this study the effect of various parameters such as initial platinum(IV)chloride
concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst
(TiO2) concentration, pH, temperature and light intensity has been investigated as a
first step towards optimising a photocatalytic batch and photocatalytic flow reactor.
Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate
constant kr as well as the adsorption equilibrium constant Ke for both the initial
platinum(IV) dependency as well as the initial ethanol concentration dependency.
The results in this study may be used in future work for the optimisation and
comparison of both batch and flow reactors towards the industrial implementation of
these processes.Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.
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Furman, Mark. "Conception et fabrication par stéréolithographie d'un catalyseur monolithique en vue de l'intensification du procédé photocatalytique pour la dépollution de l'air." Thesis, Vandoeuvre-les-Nancy, INPL, 2006. http://www.theses.fr/2006INPL096N/document.
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Ce travail a pour objet d’améliorer les performances d’un réacteur photocatalytique tubulaire de traitement des COVs, en le garnissant avec des supports structurés et imprégnés de TiO2. Grâce à un montage adapté, l’efficacité du réacteur est suivie en mesurant le taux de conversion du méthanol, choisi comme polluant modèle. Différentes géométries de support catalytique ont été fabriquées par stéréolithographie. Parmi toutes les géométries testées, la structure alvéolaire, constituée de canaux verticaux pour le passage du fluide et de canaux horizontaux pour le passage de la lumière, permet une efficacité optimale du réacteur. La modélisation du réacteur, tenant compte de la distribution de la lumière dans le support, montre que le transfert de matière est limitant lorsque le diamètre des canaux est plus petit que 4 mm. En revanche, lorsque le diamètre des canaux est supérieur à 5 mm, le manque d'efficacité est dû à une diminution de l'absorption de la lumière incidenteThe aim of the work is to improve the efficiency of a photocatalytic tubular reactor for VOCs abatement, while loading it with structured catalytic supports impregnated of TiO2.Thanks to a photocatalytic set-up , the efficiency of the reactor is followed by measuring the conversion rate of a model pollutant: methanol. Different geometries of support have been made by stereolithography. Among all tested geometries, the alveolar structure, composed of vertical channels for light penetration, and horizontal channels for the circulation of the gas flow, leads to an optimal degradation of the pollutant. The modelling of the reactor, taking into account the light distribution, shows that the mass transfer is limiting when the diameter of the channels is smaller than 4 mm. On the other hand, when the diameter of the channels is bigger than 5 mm, the lack of efficiency is due to a reduction of the absorption of the incident light by the catalytic surface
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Charles, Guillaume. "Conception et caractérisation de microréacteurs photocatalytiques." Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL012N/document.
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L'objectif général du travail de recherche était l'amélioration de la compréhension de la réaction de dégradation photocatalytique de l’acide salicylique choisi comme polluant modèle. Un réacteur ouvert ayant un canal parallélépipédique, de largeur et de profondeur de l'ordre du millimètre, imprégné de catalyseur TiO₂ , a permis de caractériser la dégradation de l’acide salicylique en fonction des dimensions du canal, du débit, de la concentration en polluant et de l’intensité d'irradiation UV. La fraction dégradée d’acide salicylique diminue avec le débit, la concentration d’entrée et augmente avec l’intensité d’irradiation UV. Pour un temps de passage donné, la réduction de la profondeur et la largeur du microcanal, améliore l’efficacité de la dégradation. En effet, d'une manière générale, la vitesse de la réaction de dégradation est proportionnelle à la surface catalytique sur le volume réactionnel. Le rapport de la surface imprégnée sur le volume du microcanal est augmenté par la miniaturisation du canal ce qui entraine une meilleure dégradation. Un modèle basé sur le modèle de Langmuir-Hinshelwood et tenant compte du transfert de matière permet de rendre compte des résultats expérimentaux. Ce modèle met en évidence que la limitation de la réaction de dégradation par le transfert de matière est plus importante aux plus faibles débits (< 10 ml/h) et quand le canal devient plus profond. La simulation prédit des taux de conversion de l’ordre de 90 %, soit en agissant sur la géométrie (réacteur multicanaux, longueur totale des canaux de l’ordre du mètre), soit sur le procédé (réacteur à recyclage fermé)The overall objective of the research work was to improve the understanding of the photocatalytic reaction of salicylic acid degradation chosen as model pollutant. An open reactor having a parallelepiped channel, of width and depth near millimetre size, coated with TiO₂ catalyst, was used to characterize the salicylic acid degradation in function of channel dimensions, flow rates, inlet pollutant concentrations and UV irradiation intensities. The degraded fraction of salicylic acid decreases with the flow rate, inlet concentration while it increases with UV irradiation intensity. For a given residence time, the reduction of the microchannel depth and width improve the degradation efficiency. Indeed, the reaction rate of degradation generally increases with the ratio of catalyst area on reaction volume. The ratio of coated area on microchannel volume is increased by miniaturization of the channel which leads to a larger degradation. A model based on the Langmuir-Hinshelwood approach which takes into account the mass-transfer account very well for the experimental results. This model highlights that reaction limitation by mass-transfer is larger at the lowest flows (< 10 mL/h) and when the channel becomes deeper. The simulation allows us to predict that conversion ratio of about 90%, can be reach by both acting on the geometry (multichannel reactor, total length of channels of the order of meter) or on the process (batch recirculation reactor)
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Farias, Manuel de Jesus Santiago. "Adsorção e oxidação eletrocatalítica do monóxido de carbono em superfícies de platina atomicamente bem-orientadas." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-25032011-103202/.
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O presente trabalho apresenta um estudo sistemático sobre a adsorção e a eletrooxidação do CO sobre eletrodos monocristalinos de platina. A partir da análise das intensidades das bandas integradas e das freqüências do Pt(111)-CO, apresenta-se uma interpretação dos efeitos de acoplamento dipolo-dipolo e de interconversão do COads.. Assim, sobre a Pt(111) os espectros de FTIR in situ mostram que o aumento na razão da intensidade das bandas integradas ACOB/ACOL e nas freqüências do νCOB quando θCO,total diminue é devido à redução do acoplamento dipolo-dipolo entre as moléculas do CO em diferentes sítios e, adicionalmente, à interconversão das formas inclinadas dos COL e COB para a forma do COB. No sentido de explicar esta interconversão, propomos um mechanism baseado nas interações dos orbitais de fronteiras do CO e do metal, associado com a retrodoação de elétrons. Nesse modelo, os deslocamentos das formas inclinadas do COL e do COB em direção à forma do COB são favoráveis provavelmente porque a retrodoação de elétrons, Ptd → CO2π* (LUMO), aumenta quando θCO,total diminui. Experimentos potenciostáticos sugerem que a cinética de nucleação e crescimento é o melhor modelo para descrever a eletrooxidação do CO. Propomos que no potencial de oxidação, ECO oxi. pode existir uma via muito rápida de formação do precursores oxigenados e que este pode lateralmente colidir com as ilhas de CO, impedindo que ocorra a dissipação das ilhas do COads. no potencial de oxidação, ECO oxi.. Apresentamos a evolução do crescimento e da oxidação de sub-monocamada de CO sobre monocristais de platina facetados. Em baixo grau de recobrimento do CO foi observado que a adsorção dessa molécula ocorre sem ocupação preferencial de sítios quinas ou terraças. Assim, sugerimos que a adsorção é um processo randômico e que depois que as moléculas do CO são adsorvidas estas não apresentam apreciáveis deslocamentos a partir de CO-(111) em direção aos sítios CO-(110). Isto significa que depois da adsorção, as moléculas do CO têm um longo tempo de residência ou que apresentam um coeficiente de difusão muito baixo. Mas, para alto grau de recobrimento por CO, os resultados mostram que é possível que laterais interações desempanham importantes papéis na distribuição de ocupação dos sítios e observamos que durante a eletrooxidação, são liberados simultaneamente sítios quinas e sítios terraços. Quanto à pré-oxidação, foi observado que quatro condições experimentais precisam ser satisfeitas para que ela ocorra sobre os monocristais de platina: (i) alto grau de recobrimento por CO; (ii) que a superfície onde oncorre a oxidação do CO tenha defeitos, como sítios quinas (110); (iii) que a camada do CO seja formada sob potenciais mais negativos do que o potencial de carga total zero do metal; (iv) e que exista pequena quantidade de CO dissolvido. As condições (i) e (ii) precisam ser satisfeitas simultaneamente para promover a pré-oxidação do CO; as condições (iii) e (iv) essencialmente contribuem correspondendo à condição (i). Observamos que a magnitude do pre-pico aumenta com o aumento do grau de recobrimento por CO. Então, isto pode ser indicativo que a pré-oxidação não tem relação com a difusão do CO em superfície porque o aumento do grau de recobrimento reduz a probabilidade de difusão em superfície. O modelo de ilhas comprimidas parece ser mais apropriado para descrever a pré-oxidação do CO.This work presents a systematic study on the CO adsorption and its oxidation at platinum single crystal electrodes. From analysis of integrated band intensity and band frequency position of the Pt(111)-CO interface in acid, it is presented an interpretation of the dipole-dipole coupling effect and surface site inter-conversions of COads.. Thus, on Pt(111), in situ FTIR data show that the increase in both ratio integrated band intensity ACOB/ACOL and frequency of νCOB when θCO,total reduces it is indicative of reduce in dipole-dipole coupling interactions between CO molecules in different surface active sites and a mechanism where the tilted COL and COB in CO pressed adlayer displace or inter-convert in favor of increase of COB concentration. In order to explain that CO interconversion, we propose a mechanism based in frontier molecular orbitals of CO and the orbitals of the metal associated with the electron back bond donation. Thus, the displacement of tilted COL and COB on the surface towards COB is more stable because probably the back bond electron donation, Ptd → CO2π* (LUMO), increase when θCO,total diminishes. Potentiostatic experiments suggest that the nucleation and growth is the better model to describe the CO oxidation. It is proposed here that close to ECO oxi. might there is a fast pathway toward formation of oxygenated species and it might reach the CO islands by side and this hinder the dissipation of COads. islands at ECO oxi.. We report also time evolution studies of low CO adsorption coverage and oxidative stripping on stepped platinum surfaces. In low CO coverage, it was observed that there is no preferential site occupancy for CO adsorption on step or terrace. It is proposed that CO adsorption onto these surfaces is a random process, and after CO adsorption there is no appreciable shift from CO-(111) to CO-(110) sites. This implies that after adsorption, CO molecules either have a very long residence time, or that the diffusion coefficient is much lower than previously thought. But, in high CO coverage, the results show that it is possible that the lateral interaction might play important role in CO site occupancy and it was observed that during the CO electrooxidation the sites released included both terrace (111) and step (110) orientations. Among the CO oxidation a clear CO preoxidation process also occurs. It was observed four experimental conditions which were verified to be fulfilled to promote CO pre-oxidation on platinum single crystal: (i) the CO coverage is should be higher than minimum threshold; (ii) the surface where CO oxidation take place should have defects, such as (110) steps; (ii) the CO monolayer should be formed at potentials below the potential of zero total charge; (iv) and in a small amount of dissolved CO should be present in the electrolyte solution. In both conditions (i) and (ii) are necessary to take place simultaneously to promote CO pre-oxidation, (iii) and (iv) essentially contribute in fulfilling condition (i). It was verified that the magnitude of pre-peak increases with the amount of CO coverage. Thus, this might indicate that the CO pre-oxidation is not having relationship with the CO diffusion on the surface, because the increase of CO coverage diminishes surface diffusion. A picture model of compressed CO islands seems the most to describe CO pre-oxidation.
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Eraso, Xavier. "Etude et modélisation cinétique individuelle et par regroupements des réactions d’hydrotraitement sur catalyseur commercial CoMo/Al2O3." Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10195/document.
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Dans un contexte de forte demande en carburants, la diversification des charges pétrolières et la sévérité des normes actuelles sur les carburants conduisent à des modifications des unités industrielles de raffinage en vue de leur optimisation. L’approche proposée dans cette thèse consiste à améliorer la description des cinétiques des réactions d’hydrotraitement des gazoles pour pouvoir prédire les effets de changements de conditions opératoires et de charge dans un simulateur du procédé industriel. La cinétique a été étudiée pour 7 charges de compositions initiales différentes sur catalyseur commercial CoMo/Al2O3 pour des températures comprises entre 320°C et 380°C à 45MPa de pression. La méthodologie adoptée a permis de balayer une gamme de soufre final allant de 5000 ppm jusqu’à quelques ppm correspondant à l’HDS ultra-profonde. Un réacteur parfaitement agité continu (Mahoney-Robinson) a été utilisé pour mesurer les vitesses de réaction. Des techniques analytiques (Sulf UV, CPG-SCD, CPG-NCD, HPLC) ont été mises au point pour quantifier les espèces soufrées, azotées et aromatiques présentes dans les gazoles. L’influence de H2, H2S, des familles de réactivité a pu ainsi être observée. Un modèle cinétique de forme Langmuir-Hinshelwood à deux sites (voies hydrogénante et désulfuration directe) pour l’HDS des espèces soufrées individuelles a été établi. Il intègre 188 paramètres cinétiques pour 33 composés et a donné des résultats satisfaisants. L’H2S est le composé le plus inhibiteur pour la voie DDS et les composés di- et tri-aromatiques pour la voie d’hydrogénation. Enfin, un modèle pour l’HDA et l’HDN des différentes familles identifiées est également proposéIn the context of a growing demand for fuel, the diversity of feedstocks and the severity of the actual specifications have led to major modifications in the industrial refinery processes for their optimization. The approach of this thesis consists in improve the kinetic descriptions of the hydrotreatment reactions of gas oils to predict the effects of operating conditions and gas oil nature changes in an industrial process simulator. The kinetic has been studied for 7 gas oils with different initial compositions over a CoMo/Al2O3 commercial catalyst for 320-380°C range of temperature and 45MPa total pressure. The methodology used in this work has permitted to cover a total sulfur range from 5000ppm to few ppm corresponding to the deep HDS. A continuous stirred tank reactor (Mahoney-Robinson) has been used to measure the reactions rates. Analytic technics (Sulf UV, CPG-SCD, CPG-NCD, HPLC) have been set to quantify the sulfur, nitrogen and aromatic species present in the gas oils. The influence of H2, H2S, individual sulfur species or reactivity groups of sulfur species, groups of aromatic and nitrogen compounds have been observed. A bi sites kinetic model (hydrogenation and direct desulfurization pathways) for the HDS of the individual sulfur species resulting from a Langmuir-Hinshelwood mechanism has been established with 188 parameters for 33 compounds and has given satisfying results. The H2S is the most inhibiting compound for the direct desulfurization and the di- and tri-aromatics for the hydrogenation. At last, a model for the HDA and HDN of the different identified families is presented as well
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Wunder, Stefanie. "Synthesis, characterization and catalytic activity of immobilized metallic nanoparticles." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16752.
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In dieser Arbeit wurden Gold- und PlatinNanopartikel in sphärischen Polyelektolyt-Bürsten (SPB) synthetisiert. Diese wurden zu mechanistischen Untersuchungen der p-Nitrophenol-Reduktion mittels Natriumborhydrid herangezogen. Dabei konnte der Mechanismus der Reaktion auf der Oberfläche der Nanopartikel aufgeklärt werden. Die Reaktion folgt einem Langmuir Hinshelwood (LH) Mechanismus. Hierbei adsorbieren beide Edukte auf die Oberfläche, bevor sie im zu p-Aminophenol umgesetzt werden. Nach der Reaktion desorbiert das Reaktionsprodukt. Mittels des LH Modells konnten für verschiedene Temperaturen die intrinsische Geschwindigkeitskonstante, sowie die Adsorptionskonstanten der Edukte bestimmt werden. Mit diesen Daten konnten dann die Enthalpie und Entropie der Adsorption der Edukte und die Aktivierungsenergie berechnet werden. Neben dem Reaktionsmechanismus wurde die Induktionszeit der p-Nitrophenol Reduktion untersucht. Hierbei konnte gezeigt werden, dass diese Totzeit der Reaktion wahrscheinlich auf eine Restrukturierung der Nanopartikeloberfläche zurückzuführen ist. Sie ist unabhängig von den eingesetzten Konzentrationen des Borhydrids, hingegen abhängig von der Konzentration an p-Nitrophenol auf der Oberfläche der Nanopartikel, was auf Restrukturierung der Nanopartikel durch p-Nitrophenol hindeutet. Zudem wurden Hinweise auf eine spontane Rekonstruktion der Nanopartikel gefunden, die unabhängig von der Konzentration des p-Nitrophenols ist. Des Weiteren wurde die katalytische Oxidation von Morin mit Manganoxid Nanopartikeln untersucht. Diese sind in der Polyelektrolytschale der SPB immobilisiert. Analysen der Reaktionskinetik der Morin Oxidation ergaben, dass auch in diesem Fall der LH Mechanismus vorliegt. Hierbei konnten die Adsorptionskonstanten und Geschwindigkeitskonstanten für verschiedene Temperaturen ermittelt werden und somit die Aktivierungsenergie der Oxidation sowie die Adsorptionsenthalpie und Entropie der Edukte.In this work, gold and platinum nanoparticles were synthesized into spherical polyelectrolyte brushes (SPB) in order to apply them as catalysts for kinetic studies of the reduction of p-nitrophenol by sodium borohydride. It was found that the reaction follows the Langmuir-Hinshelwood (LH) mechanism where both educts must adsorb onto the surface of the catalyst in order to react. Thereby, the rate determining step is the surface reaction of both educts. After the reaction, the product desorbs from the surface and a free active site is formed. With this model the intrinsic reaction rate and the adsorption constants for both educts could be determined. The measurements at different temperatures allowed the calculation of the activation energy and the adsorption enthalpy and entropy of the educts. Besides the reaction mechanism, the induction time of the reaction was analyzed. Here, it was shown that the reason of this delay time is a restructuring of the nanoparticle surface. The induction time is solely dependent on the concentration of p-nitrophenol on the surface of the nanoparticles and independent of the applied concentrations of borohydride. Moreover, hints for a spontaneous reconstruction of the nanoparticles without p-nitrophenol were found. In the second part, the catalytic oxidation of morin by manganese oxide has been studied. These nanoparticles were embedded inside the polyelectrolyte layer of the SPB. These nanoparticles were used for systematic studies of the oxidation of morin with hydrogen peroxide. It was shown that in this case the reaction followed a LH kinetics as well. Here, the intrinsic rate constants and the adsorption constants could be obtained for different temperatures. The activation energy and the adsorption enthalpy and entropy could be determined accordingly. The adsorption enthalpy is exothermic in both cases.
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Bedra, Larbi. "Étude de la recombinaison de l'oxygène atomique sur des céramiques à haute température : détermination expérimentale du coefficient de recombinaison en relation avec la microstructure - modélisation des mécanismes réactionnels." Perpignan, 2005. http://www.theses.fr/2005PERP0644.
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La rentrée atmosphérique terrestre d'un engin spatial engendre des phénomènes physico-chimiques responsables d'un échauffement dangereux pour le revêtement thermique extérieur. Une partie non négligeable de cette élévation de température est due aux mécanismes de recombinaison hétérogène de l'oxygène atomique. L'objectif, en vue de la réalisation de futurs véhicules réutilisables, est de diminuer l'énergie due aux réactions chimiques hétérogènes transférée au bouclier thermique et ainsi de prolonger leur utilisation. L'objectif de cette thèse est de quantifier les influences de la pression, de la température et de la microstructure sur la catalycité des surfaces à haute température. La mesure expérimentale du coefficient de recombinaison de l'oxygène atomique a été réalisée sur surfaces céramiques. Le montage expérimental MESOX est original car il associe un générateur de plasma micro-ondes et un concentrateur solaire qui permet de porter les échantillons à très haute température. Les caractéristiques de la phase gazeuse, température et concentration de l'oxygène atomique, sont déterminées à partir de méthodes spectroscopiques d'émission optique. Au cours de ce travail, l'impact des impuretés, présentes dans le solide, est mis en évidence sur trois alumines de même structure cristalline (lpha) mais comportant des taux et des natures d'impuretés différents. Pour compléter l'étude expérimentale, une simulation par dynamique moléculaire a été également menée pour décrire la recombinaison hétérogène des atomes d'oxygène gaz sur du quartz à l'échelle atomique. Les très bons résultats obtenus par la méthode de simulation semi-classique ouvrent de grands espoirsThe atmospheric re-entry of a space vehicle on earth leads to physico-chemical phenomena responsable of a dangerous heating of the external thermal protection. One non negligeable part of this temperature increase is due to the mechanisms of the heterogeneous recombination of atomic oxygen. The objective, to realize future reusable vehicles, is to dicrease the energy due to the heterogeneous chemical reactions transferred to the thermal shield and thus to increase their lifetime. The objective of this thesis is to quantify the influences of pressure, of temperature and of the microstructure on the catalycity of surfaces at high temperature. The experimental measurement of the recombination coefficient of atomic oxygen was realized on ceramic surfaces. The experimental set-up MESOX is unique as it associates a microwave plasma generator and a solar concentrator that allows to heat samples to very high temperatures. The characteristics of the gaseous phase, temperature and concentration of atomic oxygen, are determined using methods based on optical emission spectroscopy. During this work, the impact of impurities, present in the solid phase, is shown on three alumina materials with the same crystalline structure (lpha) but with different levels and nature of impurities. To complete the experimental study, a molecular dynamic simulation, was also performed to describe the heterogeneous recombination of the gaseous atomic oxygen on quartz at the atomic scale. The very good results obtained by the semi-classical simulation method open great hopes
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Farias, Manuel de Jesus Santiago. "Eletrooxidações de acetaldeído comum e etanol isotopicamente marcado (H3 13C-12CH2OH) em superfície de platina policristalina acompanhadas por FTIRS in situ." Universidade Federal do Maranhão, 2006. http://tedebc.ufma.br:8080/jspui/handle/tede/1561.
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This is work treat of the acetaldehyde and labeled ethanol oxidations, both kinds in percloric acidic medium, 0,1 Mol L-1 HClO4 on the Pt polycrystalline surface with used conventional electrochemical and spectroscopy techniques (FTIRS in situ). From acetaldehyde, wanted to find the mean concentration that better favor the reaction to evolve for CO2 in the potential smaller from production of the kind. The concentration 0,01 Mol L-1 was better suitable, but the increase of the concentration in solution, this is pathway was whole inhibited. However, in the high potential the form to acetic acidic is favorable. For main cronoamperometry, acetaldehyde in the concentration 0,02 Mol L-1, were able proof results in situ FTIRS. According to potential, this is results was interpreted second pattern to consider: the pear adsorbed kinds (Langmuir-Hinshelwood) and other where consider only one adsorbed kinds between adsorbed (pattern Eley-Rideal mechanism). In the case of ethanol labeled oxidation (H3 13CO 12CH2OH), it is search to look into the path delineated from way severous of the reaction from to form CO2. The results showed that is product would to be results of the intermediates oxidations contained carbon from alcohol group and intermediates contained carbon from group methyl; however, the intermediates contained carbon alcohol group is mores able reactive in the zone potential searched in the work, is this mores, confronted with able reactive metil group. The path double that yield CO2 in the zone potential below 1,0 V, are yielded coupling bands 12COL and 13COL which coexist in below potential. In the presence kind 13COL in 0,4 V potential proof that of the efficiency of the platinum electrode for the oxygenation group metil in the zone below potential. In the potential largest that 1,0 V, where exist the formation continuous of carbon dioxide, the difference in the greatness bands associated from 12CO2 e 13CO2 (double path product contained carbon), was interpreted in the sense of the electrochemical conditions infortunable for remover hydrogen group metil; additional this is kind was to promote for yield from molecules, which not is able identify for whole technique.
Este trabalho trata das reações de eletrooxidações de acetaldeído comum e etanol isotopicamente marcado, ambas reações em superfície de platina policristalina em meio de ácido perclórico, HClO4, 0,1 Mol L-1, com a utilização de técnicas eletroquímicas convencionais e espectroscopia (FTIRS in situ). Para o acetaldeído, essa reação foi estuda com a dependência do potencial aplicado e a concentração do aldeído em solução, que melhor resultaram na transformação desta molécula a CO2. Assim, para o potencial 0,6 V, a concentração de aldeído 0,01 Mol L-1 foi a mais apropriada deduzida a partir de FTIRS in situ e, a concentração 0,02 Mol L-1 permitiu a geração de maior densidade de corrente e foi inferida a partir de cronoamperometria. Essa discrepância foi discutida em termos das reações específicas que resultam no sinal analítico para cada técnica. Dependendo da concentração do acetaldeído, a via de formação de CO2 foi completamente inibida e, em altos potenciais, prevalecia sempre a formação de ácido acético. Paralelamente, dependendo do potencial, estes resultados foram interpretados com base em modelos de mecanismos de reações que considera: um par de reagentes adsorvidos (mecanismo Langmuir-Hinshelwood) e apenas uma espécie adsorvida do par fundamental de reagentes (mecanismo Eley-Rideal). Para o etanol isotopicamente marcado (H3 13C 12CH2OH), foram investigados passos delineados pelas diferentes vias de reação de formação de CO2. Os resultados mostraram que este produto pode ser resultante da eletrooxidação de intermediários contendo o carbono do grupo álcool e do grupo metil, sendo que o intermediário contendo o carbono do grupo álcool, para toda a faixa de potenciais investigados, é bem mais reativo que o intermediário contendo o carbono do grupo metil. As vias duplas que geram CO2 em potenciais abaixo de 1,0 V são resultantes de bandas acopladas de 12COL e 13COL que coexistem em baixos potenciais. A presença de 13COL em 0,35 V foi encarada como uma evidência da eficiência da Pt para oxigenação do grupo metil em baixos potenciais. Em potenciais acima de 1,0 V, onde há produção contínua de dióxido de carbono, a diferença na magnitude das intensidades de bandas relativa ao 13CO2 e 12CO2 (das vias de origem de carbono), foi interpretada como sendo as referidas condições eletroquímicas desfavoráveis para desprotonação do metil.
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Gu, Sasa. "Catalytic activity analysis of metallic nanoparticles by model reactions." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19297.
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In dieser Arbeit wurden zwei katalytische Modellreaktionen studiert. Zunächst die katalytische Reduktion von p-Nitrophenol (Nip) mit Natriumborhydrid (BH_4^-). Diese verläuft entlang der direkten Route: Dabei wird Nip über p-Hydroxylaminophenol (Hx) zum Produkt p-Aminophenol (Amp) reduziert. Ein kinetisches Modell wird vorgestellt, dass die Reaktion auf Basis des Langmuir-Hinshelwood (LH) Mechanismus beschreibt. Die Lösung der Gleichungen gibt die Nip Konzentration als Funktion der Zeit, welche direkt mit den experimentellen Daten verglichen werden kann. Werden als Katalysator auf sphärischen Polyeletrolytbürsten stabilisierte Gold Nanopartikel (SPB-Au) verwendet, zeigt sich eine gute Übereinstimmung und unterstreicht die Allgemeingültigkeit der direkten Route.
Der zweite Teil beschäftigt sich mit der katalytischen Oxidation von 3,3’,5,5’-Tetramethylbenzidin (TMB) durch Wasserstoffperoxid (H_2O_2) an SPB-Pt Nanopartikeln. Dabei wurden die Katalyse mithilfe zweier Modelle analysiert: Michaelis-Menten (MM) und Langmuir-Hinshelwood (LH). Im MM Modell wird die Oxidation von TMB durch die Nanopartikel mit der Peroxidase katalysierten TMB Oxidation unter Annahme des Ping-Pong Mechanismus verglichen. Es wurde gezeigt, dass die häufig verwendete Analyse der initialen Reaktionsraten große Fehler verursacht und zu inkonsistenten Ergebnissen führt. Dies zeigt dass dieses Vorgehen zu Analyse der Oxidation von TMB nicht geeignet ist.
Im LH Modell wird angenommen dass H_2O_2 und TMB im ersten Schritt auf der Oberfläche der Nanopartikel adsorbieren. Das LH Modell mit Produktinhibition ermöglicht hierbei eine zufriedenstellende Beschreibung der kinetischen Daten bis zu einem Umsatz von 40 %. Die gesamte Analyse zeigt, dass das Langmuir-Hinshelwood Modell die bessere Näherung zur Beschreibung der Kinetik der Nanopartikel katalysierten TMB Oxidation bietetIn this work, two catalytic model reactions were studied using different metallic nanoparticles in aqueous solution. One is the catalytic reduction of p-nitrophenol (Nip) by sodium borohydride (BH_4^-). The reaction proceeds in the following route: Nip is first reduced to p-hydroxylaminophenol (Hx) which is further reduced to the final product p-aminophenol (Amp). Here we present a full kinetic scheme according to Langmuir-Hinshelwood mechanism (LH). The solution of the kinetic equations gives the concentration of Nip as the function of time, which can be directly compared with the experimental data. Satisfactory agreement is found for reactions catalyzed by Au nanoparticles immobilized in spherical polyelectrolyte brushes (SPB-Au) verifying the validity of the reaction route. In the second part, we present a study on the catalytic oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB) by hydrogen peroxide (H_2O_2) with SPB-Pt nanoparticles. The catalysis was analyzed by two different models: Michaelis-Menten (MM) and Langmuir-Hinshelwood (LH) model. In the MM model, the oxidation of TMB catalyzed by nanoparticles is inferred to the catalysis of peroxidase assuming the Ping-Pong mechanism. It is found that the frequently used analysis with the initial rates introduces large errors and leads to inconsistent results, which indicates that such approach is not suitable to analyze the oxidation of TMB catalyzed by nanoparticles. In the LH model, it is assumed that H_2O_2 and TMB adsorb on the surface of nanoparticles in the first step. The LH model with product inhibition gives satisfactory description of the kinetic data up to a conversion of 40%. The entire analysis demonstrates that the Langmuir-Hinshelwood model provides a superior approach to describe the kinetics of TMB oxidation catalyzed by nanoparticles.
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Morisset, Sabine. "Dynamique de la formation d'hydrogène moléculaire sur une poussière interstellaire." Phd thesis, Université Paris Sud - Paris XI, 2004. http://tel.archives-ouvertes.fr/tel-00008537.
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Dans le milieu interstellaire (MIS), la formation de la molécule H_2 est catalysée par un grain de poussière : H+H+grain -> grain+ H_2 Deux mécanismes principaux correspondent à cette réaction: le mécanisme Eley-Rideal (ER) et le mécanisme Langmuir-Hinshelwood (LH). Les techniques de propagation de paquets d'ondes ont été utilisées pour étudier ces deux mécanismes aux faibles températures qui règnent dans le MIS. Pour rendre possible le calcul, il a fallu utiliser une grille en L et appliquer la technique de réduction de grille dite de « mapping » sur des grilles multidimensionnelles. Ceci a permis de couvrir une gamme d'énergie de collision comprise entre 0,4meV et 46meV pour le mécanisme ER, et entre 4meV et 50meV pour le mécanisme LH. Le mécanisme ER a été étudié en géométrie colinéaire sur une surface de graphite (0001), en autorisant le mouvement d'un atome de carbone du grain. Permettre cette relaxation du substrat favorise la réaction. Toutefois le mécanisme ER reste peu efficace dans les conditions de température régnant dans le MIS, du fait d'une petite bosse de potentiel en voie d'entrée. Le mécanisme LH a lui été étudié dans toute sa dimensionnalité sur une surface plane et rigide. Le résultat principal est que ce mécanisme est très efficace : dans des conditions caractéristiques du MIS, le temps mis par un atome H pour diffuser sur le grain, rencontrer un autre atome H, et désorber en H2 est inférieur au temps typique entre deux collisions H-grain. La réaction n'a aucun effet notable sur le rapport ortho- H_2 et para- H_2. En revanche, comme dans le mécanisme ER, elle conduit à une très forte excitation vibrationnelle de H_2.
Book chapters on the topic "Langmuir-Hinshelwood"
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Irvine, William M. "Langmuir-Hinshelwood Mechanism." In Encyclopedia of Astrobiology, 1. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-27833-4_863-3.
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Irvine, William M. "Langmuir-Hinshelwood Mechanism." In Encyclopedia of Astrobiology, 1360. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-44185-5_863.
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Irvine, William M. "Langmuir-Hinshelwood Mechanism." In Encyclopedia of Astrobiology, 905. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-11274-4_863.
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Irvine, William M. "Langmuir-Hinshelwood Mechanism." In Encyclopedia of Astrobiology, 1. Berlin, Heidelberg: Springer Berlin Heidelberg, 2021. http://dx.doi.org/10.1007/978-3-642-27833-4_863-4.
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Caycedo Villalobos, Luis Alejandro. "Langmuir–Hinshelwood Mechanism Implemented in FPGA." In Communications in Computer and Information Science, 317–27. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-030-00350-0_27.
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Shahbazi, Fatemeh, Masoud Jabbari, Mohammad Nasr Esfahani, and Amir Keshmiri. "Numerical Simulation of Langmuir-Hinshelwood Mechanism for Heterogeneous Biosensors in Microfluidic Channel." In 8th European Medical and Biological Engineering Conference, 905–14. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-64610-3_101.
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Edidiong, Okon, Shehu Habiba, and Gobina Edward. "Validation of a Novel Method for Ethyl Lactate Separation Using Langmuir Hinshelwood Model." In Transactions on Engineering Technologies, 499–512. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-2717-8_35.
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Doraiswamy, L. K. "Catalysis by Solids, 2 : The Catalyst and Its Microenvironment." In Organic Synthesis Engineering. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195096897.003.0013.
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Solid catalysts by their very nature involve diffusion of reactant fluids within their matrix. These fluids react even as they diffuse. Thus the problem of internal diffusion accompanied by reaction becomes important. Another problem of equal importance is the transport of the reactant from the fluid bulk to the catalyst surface—often referred to as external diffusion. Together these constitute the microenvironment of the catalyst pellet and form the subject matter of this chapter. Consider the reaction between aniline and methanol on pellets of alumina to give dimethylaniline: Let the pellets be placed in a flowing stream of reactants inside a tubular reactor. Restricting our attention now to a single pellet and its immediate environment, the various steps involved in the overall process are shown in Figure 7.1. This physical-chemical circuit is built in analogy with the electrical circuit shown at the bottom of the figure. Clearly, the overall process is a complex combination of chemical and physical steps. Note, however, that the mathematical analysis of the parallel pathways (diffusion and reaction) is not always based on the addition of reciprocal resistances as in parallel electrical circuits but on the fact that the two occur simultaneously on a single pathway, that is, the molecule reacts even as it diffuses. The construction of a model based on one of the adsorption-reactiondesorption steps being the limiting step constitutes the core of the semiempirical approach considered in this chapter. In this approach, the microscopic origins of the observed macroscopic effects of catalysts (as described by many authors, e.g., Plath, 1989) are ignored. The models thus developed are commonly known as Langmuir-Hinshelwood models among chemists and as Hougen-Watson models among chemical engineers. We choose to call them Langmuir-Hinshelwood-Hougen-Watson (LHHW) models. For a more basic approach to kinetic modeling of catalytic reactions in general, reference may be made, among others, to Compton (1991) and Van Santen and Niemantsverdriet (1995). In the interest of generality, we consider hypothetical reactions and derive rate equations for a few typical LHHW models (Hougen and Watson, 1947; Yang and Hougen, 1950; Satterfield, 1980, Butt, 1980; Doraiswamy and Sharma, 1984; Boudart and Djéga-Mariadassou, 1984)..
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Zhao, Xueliang, Fanxing Li, and Dezheng Wang. "Comparison of microkinetics and Langmuir-Hinshelwood models of the partial oxidation of methane to synthesis gas." In Studies in Surface Science and Catalysis, 235–40. Elsevier, 2004. http://dx.doi.org/10.1016/s0167-2991(04)80057-0.
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Doraiswamy, L. K. "Multiphase Reactions and Reactors." In Organic Synthesis Engineering. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195096897.003.0025.
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The first three chapters of this part dealt with two-phase reactions. Although catalysts are not generally present in these systems, they can be used in dissolved form in the liquid phase. This, however, does not increase the number of phases. On the other hand, there are innumerable instances of gas-liquid reactions in which the catalyst is present in solid form. A popular example of this is the slurry reactor so extensively employed in reactions such as hydrogenation and oxidation. There are also situations where the solid is a reactant or where a phasetransfer catalyst is immobilized on a solid support that gives rise to a third phase. A broad classification of three-phase reactions and reactors is presented in Table 17.1 (not all of which are considered here). This is not a complete classification, but it includes most of the important (and potentially important) types of reactions and reactors. The thrust of this chapter is on reactions and reactors involving a gas phase, a liquid phase, and a solid phase which can be either a catalyst (but not a phasetransfer catalyst) or a reactant, with greater emphasis on the former. The book by Ramachandran and Chaudhari (1983) on three-phase catalytic reactions is particularly valuable. Other books and reviews include those of Shah (1979), Chaudhari and Ramachandran (1980), Villermaux (1981), Shah et al. (1982), Hofmann (1983), Crine and L’Homme (1983), Doraiswamy and Sharma (1984), Tarmy et al. (1984), Shah and Deckwer (1985), Chaudhari and Shah (1986), Kohler (1986), Chaudhari et al. (1986), Hanika and Stanek (1986), Joshi et al. (1988), Concordia (1990), Mills et al. (1992), Beenackers and Van Swaaij (1993), and Mills and Chaudhari (1997). Doraiswamy and Sharma (1984) also present a discussion of gas-liquid-solid noncatalytic reactions in which the solid is a reactant. In Chapter 7 we saw how Langmuir-Hinshelwood-Hougen-Watson (LHHW) models are normally used to describe the kinetics of gas-solid (catalytic) or liquid-solid (catalytic) reactions, and in Chapters 14 to 16 we saw how mass transfer between gas and liquid phases can significantly alter the rates and regimes of these two-phase reactions.
Conference papers on the topic "Langmuir-Hinshelwood"
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Gokon, Nobuyuki, Yusuke Osawa, Daisuke Nakazawa, Tsuyoshi Hatamachi, and Tatsuya Kodama. "Kinetics of CO2 Reforming of Methane by Catalytically Activated Metallic Foam Absorber for Solar Receiver-Reactors." In ASME 2008 2nd International Conference on Energy Sustainability collocated with the Heat Transfer, Fluids Engineering, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/es2008-54156.
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Ni-Cr-Al alloy foam absorber with high porosity was catalytically activated using a Ru/γ-Al2O3 catalyst, and was subsequently tested with respect to CO2 reforming of methane in a small-scale volumetric receiver-reactor by using a sun simulator. A chemical storage efficiency of about 40% was obtained for a mean light flux of 325 kWm−2. Furthermore, the activity and the stability of the metallic foam absorber were compared with those of a SiC foam absorber activated with the same Ru/γ-Al2O3 catalyst for 50 h of light irradiation, and it was found that the metallic foam absorber has superior catalytic stability in comparison to the SiC form absorber. In addition, unlike ceramic foams such as SiC, metallic foams feature superior plasticity, which prevents the emergence of cracks caused by mechanical or thermal shock. The kinetics of CO2 reforming of methane over metallic foam absorbers were also examined for temperatures of 600–750°C using a quartz tube reactor and an electric furnace. The experiments were performed by varying the methane/CO2 ratios of 0.5–2.3. Moreover, the kinetic data were fitted to four different types of kinetic models, namely the Langmuir-Hinshelwood, Basic, Eley-Rideal, and Stepwise mechanisms. The kinetic model which provided the best prediction of the experimental reforming rates was the Langmuir-Hinshelwood mechanism.
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Gellman, Andrew J., and Yang Yun. "Issues in Vapor Phase Lubrication of Magnetic Data Storage Media." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63165.
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Vapor phase lubrication (VPL) integrates media lubrication with the vacuum processing steps used throughout most of the hard disk media fabrication process. This avoids exposure of the unlubricated a-CHx overcoat surface to the ambient air and airborne contamination. In vapor lubrication the a-CHx surface can be oxidized under controlled conditions immediately prior to lubricant adsorption. The kinetics of a-CHx oxidation have been studied using x-ray photoemission spectroscopy in an apparatus that allows oxidation of freshly deposited a-CHx films. The dissociative sticking coefficient of oxygen is ∼10−6 and the initial oxidation kinetics can be described by a Langmuir-Hinshelwood mechanism.
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Lee, Shinku, Joongmyeon Bae, and Sungkwang Lim. "Numerical Thermal and Mass Analyses of Autothermal Reformer." In ASME 2006 4th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2006. http://dx.doi.org/10.1115/fuelcell2006-97158.
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This paper discusses numerical analysis of heat and mass transfer characteristics in autothermal fuel reformer. Assuming local thermal equilibrium between bulk gas and surface of catalyst, one medium approach for energy equation is incorporated. Also, mass transfer between concentrations of bulk gas and near the surface of catalyst is neglected due to relatively low gas mixture velocity. For surface chemical reaction Langmuir-Hinshelwood reaction is incorporated when methane (CH4) is reformed to hydrogen-rich gases by autothermal reforming (ATR) reaction. Complete combustion, steam reforming, water gas shift and direct methane steam reforming reactions are included in the chemical reaction model. Under two operating conditions (O/C and S/C), ATR reactions are estimated from the numerical calculations. Mass, momentum, and energy equations are simultaneously calculated with chemical reactions. From the predicted results, we can estimate optimum operating conditions for high hydrogen yield.
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Stamatiou, Anastasia, Peter G. Loutzenhiser, and Aldo Steinfeld. "Solar Syngas Production From H2O and CO2 via Two Step Thermochemical Cycles Based on FeO/Fe3O4 Redox Reactions: Kinetic Analysis." In ASME 2010 4th International Conference on Energy Sustainability. ASMEDC, 2010. http://dx.doi.org/10.1115/es2010-90009.
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Syngas production via a two-step H2O/CO2-splitting thermochemical cycle based on FeO/Fe3O4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of Fe3O4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO2 and H2O with FeO to CO and H2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with FeO in the range 973–1273 K and CO2/H2O concentrations of 15–75%. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir-Hinshelwood type was formulated to describe the competitiveness of the reaction based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.
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Kumar, Mayank, Cheng Zhang, Rory F. D. Monaghan, Simcha L. Singer, and Ahmed F. Ghoniem. "CFD Simulation of Entrained Flow Gasification With Improved Devolatilization and Char Consumption Submodels." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-12982.
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In this work, we use a CFD package to model the operation of a coal gasifier with the objective of assessing the impact of devolatilization and char consumption models on the accuracy of the results. Devolatilization is modeled using the Chemical Percolation Devolitilization (CPD) model. The traditional CPD models predict the rate and the amount of volatiles released but not their species composition. We show that the knowledge of devolatilization rates is not sufficient for the accurate prediction of char consumption and a quantitative description of the devolatilization products, including the chemical composition of the tar, is needed. We incorporate experimental data on devolatilization products combined with modeling of the tar composition and reactions to improve the prediction of syngas compositions and carbon conversion. We also apply the shrinking core model and the random pore model to describe char consumption in the CFD simulations. Analysis of the results indicates distinct regimes of kinetic and diffusion control depending on the particle radius and injection conditions for both char oxidation and gasification reactions. The random pore model with Langmuir-Hinshelwood reaction kinetics are found to be better at predicting carbon conversion and exit syngas composition than the shrinking core model with Arrhenius kinetics. In addition, we gain qualitative and quantitative insights into the impact of the ash layer surrounding the char particle on the reaction rate.
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De La Pena-Cortes, Ernesto, Francisco Elizalde-Blancas, Abel Hernandez-Guerrero, Armando Gallegos-Munoz, and Juan M. Belman-Flores. "Numerical Analysis of the Internal Fuel Processing in Solid Oxide Fuel Cells." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-65273.
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The high operating temperature of a SOFC (solid oxide fuel cell) has several consequences, from which the most important one is the possibility to feed the cell directly with unprocessed fuels. This eliminates the need for expensive external fuel reformers that hinder the cell from achieving a greater overall efficiency when coupled into a power generation system. Direct internal reforming (DIR) takes place directly on the anode of a SOFC by harnessing the available Nickel catalyst on its surface to process the incoming fuel. In this study a three dimensional steady state computational fluid dynamics model is implemented in a planar DIR SOFC to compare the overall cell performance operating on biogas, and coal syngas. Since chemical kinetics plays a significant role in the model accuracy, the present work also focuses on comparing three different chemical reaction mechanisms for the internal reforming process. These include a detailed heterogeneous mechanism consisting of 42 elementary reactions, a global homogeneous catalyzed mechanism, and a Langmuir-Hinshelwood based mechanism. The former includes autothermal reforming, steam reforming and water gas shift reaction effects, the latter two include steam reforming, and water gas shift reaction effects. The analysis yields detailed information about the cell, including polarization curves that help to assess the cell performance for each fuel. Meanwhile the chemical kinetics comparison amongst the analyzed mechanisms helps in establishing the best compromise between the accuracy of the model, and the computational resources devoted for the calculation.
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Gharebaghi, M., B. Goh, J. M. Jones, L. Ma, M. Pourkashanian, and A. Williams. "Numerical Investigation of Char Reactivity in Oxy-Coal Combustion in Carbon Capture and Sequestration Technologies." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59887.
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Oxy-coal combustion with CO2 capture from flue gas is an emerging technology that can be adapted to both new and existing coal-fired power stations leading to substantial reduction in carbon emission from the power generation industry. However, switching to oxy-coal brings a number of uncertainties to the combustion process and there is a significant knowledge gap in this new technology. Computational Fluid Dynamic (CFD) studies can be used as one of the tool to identify the extent of the modifications required due to changes in the process. One of the possible challenges is related to the the changes in char combustion and char reactivity which may have an impact on unburned carbon in the furnace. In this study, two approaches have been undertaken to investigate the impact of oxy-coal combustion on char reactivity: simple equilibrium calculations and numerical 3-D simulations. As the focus of this study, the influence of CO2-O2 combustion environment on char reactivity and particularly carbon in ash has been investigated. It has been found that the effect of C-CO2 and C-H2O reactions on overall char reactivity cannot be disregarded. In addition, in this study, it is suggested that using the Langmuir-Hinshelwood mechanism can provide a more accurate prediction for the effect of gasification reactions on unburnt carbon and char reactivity. The accuracy of the CFD modeling has been investigated using experimental data from a one MWth combustion test facility. In order to improve the validity of the CFD code for design purposes, further modeling improvements for accurate predictions are addressed.
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Basu, Sumit, Yuan Zheng, and Jay P. Gore. "Chemical Kinetics Parameter Estimation for Ammonia Borane Hydrolysis." In ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/ht2008-56139.
Full textAbstract:
Onboard hydrogen storage is an enabling factor in the development of fuel cell powered passenger cars. Ammonia borane (AB) hydrolysis is one of the potential technologies for onboard hydrogen storage. In this study, kinetics of catalyzed ammonia borane hydrolysis using ruthenium-supported-on-carbon has been measured. For reacting flows, chemical kinetics determines the rates of heat generation and species production or consumption in the overall energy and mass balances respectively. Kinetic measurements under isothermal conditions provide critical data for the design of hydrolysis reactors. It is, however, not always possible to eliminate the effects of internal diffusion in a heterogeneous chemical reaction. In such cases, the reaction efficiency (η), which depends on the effective liquid phase diffusivity (Deff) in the catalyst medium, should be determined. Determination of intrinsic kinetic parameters using apparent kinetics data is, thus, a challenge. In this study, the change in AB concentration (CAB) with reaction time (t) has been directly measured. It was observed that the AB hydrolysis reaction had orders between zero and one in a temperature range of 26°C to 55°C. A unified Langmuir-Hinshelwood (LH) model has been adopted to describe the reaction kinetics. The intrinsic kinetic parameters (A, Ea, ΔHads, K0) as well as Deff need to be estimated by inverse analysis of the measured CAB vs t data. Conventionally, kinetic parameters are determined using linear fitting. Sometimes, however, it is impossible to converge to a unique value by using the linear fitting approach as there are several values providing regression coefficients greater than 0.99. In this study, the multiple-variable inverse problem has been solved using a nonlinear fitting algorithm based on Powell’s conjugate-gradient error minimization. This algorithm minimizes errors without using derivatives. As a result, the uncertainties in the kinetic parameter estimation have been significantly reduced by the new approach.
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Toema, Mohamed, and Kirby S. Chapman. "Interpreting the Lambda Sensor Output Signal to Control Emissions From Natural Gas Fueled Engines." In ASME 2010 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/icef2010-35164.
Full textAbstract:
This paper presents the work done to date on a modeling study of the Non-Selective Catalytic Reduction (NSCR) system. Several recent experimental studies indicate that the voltage signal from the heated exhaust gas oxygen sensor commonly used to control these emission reduction systems may not be interpreted correctly because of the physical nature in the way the sensor senses the exhaust gas concentration. While the current signal interpretation may be satisfactory for modest NOX and CO reduction, an improved understanding of the signal is necessary to achieve consistently low NOX and CO emission levels. The increasingly strict emission regulations may require implementing NSCR as a promising emission control technology for stationary spark ignition engines. Many recent experimental investigations that used NSCR systems for stationary natural gas fueled engines showed that NSCR systems were unable to consistently control the emissions level below the compliance limits. Modeling of NSCR components to better understand, and then exploit, the underlying physical processes that occur in the lambda sensor and the catalyst media is now considered an essential step toward improving NSCR system performance. This paper focuses only on the lambda sensor that provides feedback to the air-to-fuel ratio controller. The goals of this modeling study are: • Improve the understanding of the transport phenomena and electrochemical processes that occur within the sensor. • Investigate the cross-sensitivity of exhaust gases from natural gas fueled engines on the sensor performance. • Serve as a tool for improving NSCR control strategies. This model simulates the output from a planar switch type lambda sensor. The model consists of three modules. The first module models the multi-component mass transport through the sensor protective layer. A one dimensional mass conservation equation is used for each exhaust gas species. Diffusion fluxes are calculated using the Maxwell-Stefan equation. The second module includes all the surface catalytic reactions that take place on the sensor platinum electrodes. All kinetic reactions are modeled based on the Langmuir-Hinshelwood kinetic mechanism. The third module is responsible for simulating the reactions that occur on the electrolyte material and determining the sensor output voltage. The details of these three modules as well as a parametric study that investigates the sensitivity of the output voltage signal to various exhaust gas parameters is provided in the paper.
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Toema, Mohamed, and Kirby S. Chapman. "Modeling of Lambda Sensor Output With Exhaust Gas Mixtures From Natural Gas-Fueled Engines." In ASME 2011 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/icef2011-60188.
Full textAbstract:
The increasingly strict emission regulations may require implementing Non-Selective Catalytic Reduction (NSCR) system as a promising emission control technology for stationary rich burn spark ignition engines. Many recent investigations used NSCR systems for stationary natural gas fueled engines showed that NSCR systems were unable to consistently control the emissions level below the compliance limits. Modeling of NSCR components to better understand, and then exploit, the underlying physical processes that occur in the lambda sensor and the catalyst media is now considered an essential step toward the required NSCR system performance. This paper presents the work done to date on a modeling of lambda sensor that provides feedback to the air-to-fuel controller. Several recent experimental studies indicate that the voltage signal from the lambda sensor may not be interpreted correctly because of the physical nature in the way the sensor senses the exhaust gas concentration. Correct interpretation of the sensor output signal is necessary to achieve consistently low emissions level. The goal of this modeling study is to improve the understanding of the physical processes that occur within the sensor, investigate the cross-sensitivity of various exhaust gas species on the sensor performance, and finally this model serves as a tool to improve NSCR control strategies. This model simulates the output from a planar switch type lambda sensor. The model consists of three modules. The first module models the multi-component mass transport through the sensor protective layer. Diffusion fluxes are calculated using the Maxwell-Stefan equation. The second module includes all the surface catalytic reactions that take place on the sensor platinum electrodes. All kinetic reactions are modeled based on the Langmuir-Hinshelwood kinetic mechanism. The model incorporates for the first time methane catalytic reactions on the sensor platinum electrode. The third module is responsible for simulating the reactions that occur on the electrolyte material and determine the sensor output voltage. The model results are validated using field test data obtained from a mapping study of a natural gas-fueled engine equipped with NSCR system. The data showed that the lambda sensor output voltage is influenced by the reducing species concentration, such as carbon monoxide (CO) and hydrogen (H2). The results from the developed model and the experimental data showed strong correlations between CO and H2 with the sensor output voltage within the lambda operating range between 0.994 to 1.007 (catalytic converter operating window). This model also showed that methane does not significantly influence the lambda sensor performance compared to the effect of CO and H2.