Catalysts

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17 pages, 3123 KiB

Open AccessFeature PaperArticle

Catalyst Stability Assessment in a Lab-Scale Liquid-Solid (LS)² Plug-Flow Reactor

by Anton De Vylder, Jeroen Lauwaert, Stijn Van Auwenis, Jeriffa De Clercq and Joris W. Thybaut

Catalysts 2019, 9(9), 755; https://doi.org/10.3390/catal9090755 - 8 Sep 2019

Cited by 9 | Viewed by 6686

A packed-bed plug-flow reactor, denoted as the lab-scale liquid-solid (LS)² reactor, has been developed for the assessment of heterogeneous catalyst deactivation in liquid-phase reactions. The possibility to measure intrinsic kinetics was first verified with the model transesterification of ethyl acetate with methanol, catalyzed [...] Read more.

A packed-bed plug-flow reactor, denoted as the lab-scale liquid-solid (LS)² reactor, has been developed for the assessment of heterogeneous catalyst deactivation in liquid-phase reactions. The possibility to measure intrinsic kinetics was first verified with the model transesterification of ethyl acetate with methanol, catalyzed by the stable commercial resin Lewatit K2629, for which a turnover frequency (TOF) of 6.2 ± 0.4 × 10⁻³ s⁻¹ was obtained. The absence of temperature and concentration gradients was verified with correlations and experimental tests. The potential for assessing the deactivation of a catalyst was demonstrated by a second intrinsic kinetics evaluation where a methylaminopropyl (MAP)-functionalized mesoporous silica catalyst was used for the aldol reaction of acetone with 4-nitrobenzaldehyde in different solvents. The cooperative MAP catalyst deactivated as a function of time on stream when using hexane as solvent. Yet, the monofunctional MAP catalyst exhibited stable activity for at least 4 h on stream, which resulted in a TOF of 1.2 ± 0.1 × 10⁻³ s⁻¹. It did, however, deactivate with dry acetone or DMSO as solvent due to the formation of site-blocking species. This deactivation was mitigated by co-feeding 2 wt % of water to DMSO, resulting in stable catalyst activity. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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21 pages, 3351 KiB

Open AccessArticle

Mass and Heat Transfer Coefficients in Automotive Exhaust Catalytic Converter Channels

by Chrysovalantis C. Templis and Nikos G. Papayannakos

Catalysts 2019, 9(6), 507; https://doi.org/10.3390/catal9060507 - 4 Jun 2019

Cited by 3 | Viewed by 3457

Abstract

Mass and heat transfer coefficients (MTC and HTC) in automotive exhaust catalytic monolith channels are estimated and correlated for a wide range of gas velocities and prevailing conditions of small up to real size converters. The coefficient estimation is based on a two [...] Read more.

Mass and heat transfer coefficients (MTC and HTC) in automotive exhaust catalytic monolith channels are estimated and correlated for a wide range of gas velocities and prevailing conditions of small up to real size converters. The coefficient estimation is based on a two dimensional computational fluid dynamic (2-D CFD) model developed in Comsol Multiphysics, taking into account catalytic rates of a real catalytic converter. The effect of channel size and reaction rates on mass and heat transfer coefficients and the applicability of the proposed correlations at different conditions are discussed. The correlations proposed predict very satisfactorily the mass and heat transfer coefficients calculated from the 2-D CFD model along the channel length. The use of a one dimensional (1-D) simplified model that couples a plug flow reactor (PFR) with mass transport and heat transport effects using the mass and heat transfer correlations of this study is proved to be appropriate for the simulation of the monolith channel operation. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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34 pages, 10669 KiB

Open AccessArticle

Modeling and Simulations of NO_x and SO₂ Seawater Scrubbing in Packed-Bed Columns for Marine Applications

by Ion Iliuta and Faïçal Larachi

Catalysts 2019, 9(6), 489; https://doi.org/10.3390/catal9060489 - 28 May 2019

Cited by 21 | Viewed by 4193

Abstract

Seawater scrubbing of nitrogen oxides and sulfur oxide from marine emissions was simulated in packed-bed columns exposed to static inclination and heaving/oscillating motions. Fourth generation random packings (Raschig super-Rings) while providing much smaller pressure drop than traditional Pall-Rings ensure comparable absorption efficiency for [...] Read more.

Seawater scrubbing of nitrogen oxides and sulfur oxide from marine emissions was simulated in packed-bed columns exposed to static inclination and heaving/oscillating motions. Fourth generation random packings (Raschig super-Rings) while providing much smaller pressure drop than traditional Pall-Rings ensure comparable absorption efficiency for the pollutants. Complete removal of SO₂ was predicted over the tested pressure range with absorption efficiency indifferent to scrubber inclination or heaving/oscillating motions. In contrast, NO_x and CO₂ absorptions are negatively impacted for inclined seawater scrubbers. Removal efficiency is not lowered significantly owing to larger scrubber pressure and because diffusion of N₂O₄ into the liquid phase is associated with a rapid pseudo first-order reaction. The asymmetrical oscillating motion of the scrubber degrades the removal performance which exhibits wavy patterns close to the steady-state solution of the average inclination angle. NO and CO₂ absorption performance waves are moving toward a steady-state solution of vertical scrubber when the asymmetry of the two inclined positions of the scrubber downgrades. Symmetric oscillation and heaving motion led to performance disturbance waves around a steady-state solution of the vertical scrubber which are determined by the parameters of angular/heaving motion. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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11 pages, 1368 KiB

Open AccessArticle

Combining Planar Laser-Induced Fluorescence with Stagnation Point Flows for Small Single-Crystal Model Catalysts: CO Oxidation on a Pd(100)

by Jianfeng Zhou, Sebastian Matera, Sebastian Pfaff, Sara Blomberg, Edvin Lundgren and Johan Zetterberg

Catalysts 2019, 9(5), 484; https://doi.org/10.3390/catal9050484 - 25 May 2019

Cited by 5 | Viewed by 2923

Abstract

A stagnation flow reactor has been designed and characterized for both experimental and modeling studies of single-crystal model catalysts in heterogeneous catalysis. Using CO oxidation over a Pd(100) single crystal as a showcase, we have employed planar laser-induced fluorescence (PLIF) to visualize the [...] Read more.

A stagnation flow reactor has been designed and characterized for both experimental and modeling studies of single-crystal model catalysts in heterogeneous catalysis. Using CO oxidation over a Pd(100) single crystal as a showcase, we have employed planar laser-induced fluorescence (PLIF) to visualize the CO₂ distribution over the catalyst under reaction conditions and subsequently used the 2D spatially resolved gas phase data to characterize the stagnation flow reactor. From a comparison of the experimental data and the stagnation flow model, it was found that characteristic stagnation flow can be achieved with the reactor. Furthermore, the combined stagnation flow/PLIF/modeling approach makes it possible to estimate the turnover frequency (TOF) of the catalytic surface from the measured CO₂ concentration profiles above the surface and to predict the CO₂, CO and O₂ concentrations at the surface under reaction conditions. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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22 pages, 6763 KiB

Open AccessArticle

Numerical Evaluation of Potential Catalyst Savings for Ventilation Air Methane Catalytic Combustion in Helical Coil Reactors with Selective Wall Coating

by Jundika C. Kurnia, Benitta A. Chaedir, Desmond C. Lim, Lianjun Chen, Lishuai Jiang and Agus P. Sasmito

Catalysts 2019, 9(4), 380; https://doi.org/10.3390/catal9040380 - 23 Apr 2019

Cited by 3 | Viewed by 4037

Abstract

During active mining operation of a gassy underground mine, large amounts of methane will be released from the mine ventilation shaft. To eliminate the harmful effects of this ventilation air methane and minimize the wastage of this potential energy resource, considerable effort has [...] Read more.

During active mining operation of a gassy underground mine, large amounts of methane will be released from the mine ventilation shaft. To eliminate the harmful effects of this ventilation air methane and minimize the wastage of this potential energy resource, considerable effort has been devoted to converting this alternative fuel using catalytic combustion. This study numerically investigated the reaction performance of ventilation air methane (VAM) in helical coil tubes of various configurations utilizing a computational fluid dynamics (CFDs) approach. Several key factors affecting the catalytic combustion performance such as curvature, inlet Reynolds number, and cross-section aspect ratio were evaluated. Recalling the high cost of the catalyst used in this reaction—platinum—optimization of catalyst usage by implementing selective catalyst coating was conducted and investigated. For evaluation purposes, the reaction performance of the helical coil tube was compared to its straight counterpart. The results gave a firm confirmation of the superior performance of the helical coil tube compared to the straight one. In addition, it was found that the selective inner wall coating in the circular cross-section at a higher Reynolds number gave rise to the highest figure of merit (FoM), defined as the net energy produced per mg of catalyst platinum. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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19 pages, 7068 KiB

Open AccessArticle

Modeling and Order Reduction for the Thermodynamics of a Diesel Oxidation Catalyst with Hydrocarbon Dosing

by Feng Wu, Benxi Zhang, Dongwei Yao and Yanxiang Yang

Catalysts 2019, 9(4), 369; https://doi.org/10.3390/catal9040369 - 18 Apr 2019

Cited by 4 | Viewed by 3709

Abstract

This paper presents an order reduction for the thermal dynamics of a diesel oxidation catalyst (DOC) with hydrocarbon (HC) dosing. The original model includes the pyrolysis of diesel droplets and a wall storage process in the upstream of the DOC. The order reduction [...] Read more.

This paper presents an order reduction for the thermal dynamics of a diesel oxidation catalyst (DOC) with hydrocarbon (HC) dosing. The original model includes the pyrolysis of diesel droplets and a wall storage process in the upstream of the DOC. The order reduction process is derived from the thermodynamics model of the DOC for further control design. The results are compared with experimental data. It is found that the DOC can be simplified as a second-order model using the HC dosing model, which has more than 94% fitness, reflecting the thermodynamics of the system. According to this research, the DOC thermal dynamics can be considered to be equivalent to a time-varying second-order system for the investigation. The second-order parameters of K, T_w, and ζ are also investigated in this paper. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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29 pages, 4110 KiB

Open AccessArticle

Laccase-Catalyzed Oxidation of Mixed Aqueous Phenolic Substrates at Low Concentrations

by Stoyan Rangelov and Jim A. Nicell

Catalysts 2019, 9(4), 368; https://doi.org/10.3390/catal9040368 - 18 Apr 2019

Cited by 6 | Viewed by 2651

Abstract

It has been proposed that Trametes versicolor laccase can be used to detoxify wastewaters that are contaminated with phenolic pollutants. However, the oxidation of phenols at low concentrations may be impacted if other substrates tend to interfere with or enhance the oxidation of [...] Read more.

It has been proposed that Trametes versicolor laccase can be used to detoxify wastewaters that are contaminated with phenolic pollutants. However, the oxidation of phenols at low concentrations may be impacted if other substrates tend to interfere with or enhance the oxidation of the target substrate. To test this, experiments were conducted to evaluate effects arising from the simultaneous presence of mixed substrates including phenol (P), estradiol (E2), cumylphenol (CP), and triclosan (TCL), each of which are characterized by different rates of oxidation and tendencies to inactivate laccase. Slower and faster substrates were found to have only minor negative impacts upon the rate of conversion of targeted substrates, except where they tended to cause inactivation. No enhancements in substrate oxidation were observed. A multi-substrate kinetic model was shown to be able to accurately predict the time course of reactions of mixed substrates over extended periods at micromolar and sub-micromolar concentrations, except when estradiol and triclosan were simultaneously present. In this case, more enzyme inactivation was observed than would be expected from the oxidation of individual substrates alone. The utility of the model for providing insights into the reaction phenomenon and for evaluating the feasibility of oxidizing targeted substrates in the presence of other substrates is demonstrated. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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23 pages, 2762 KiB

Open AccessArticle

Analysis of Mass Transport through Anisotropic, Catalytic/Bio-Catalytic Membrane Reactors

by Endre Nagy and Márta Vitai

Catalysts 2019, 9(4), 358; https://doi.org/10.3390/catal9040358 - 13 Apr 2019

Cited by 4 | Viewed by 3010

Abstract

This paper investigated the steady-state mass transport process through anisotropic, composite membrane layers with variable mass transport coefficients, such as the diffusion coefficient, convective velocity, or chemical/biochemical reaction rate constant. The transfer processes can be a solution-diffusion model or diffusive plus convective process. [...] Read more.

This paper investigated the steady-state mass transport process through anisotropic, composite membrane layers with variable mass transport coefficients, such as the diffusion coefficient, convective velocity, or chemical/biochemical reaction rate constant. The transfer processes can be a solution-diffusion model or diffusive plus convective process. In the theoretical part, the concentration distribution as well as the inlet and outlet mass transfer rates’ expressions are defined for physical transport processes with variable diffusion or solubility coefficients and then that for transport processes accompanied by first- and zero-order reactions, in the presence of diffusive and convective flow, with constant and variable parameters. The variation of the transport parameters as a function of the local coordinate was defined by linear equations. It was shown that the increasing diffusion coefficient or convective flow induces much lower concentrations across the membrane layer than transport processes, with their decreasing values a function of the space coordinate. Accordingly, this can strongly affect the effect of the concentration dependent chemical/biochemical reaction. The inlet mass transfer rate can also be mostly higher when the transport parameter decreases across the anisotropic membrane layer. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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19 pages, 3801 KiB

Open AccessArticle

Micro-Kinetic Modelling of CO-TPD from Fe(100)—Incorporating Lateral Interactions

by Thobani G. Gambu, R. Kyle Abrahams and Eric van Steen

Catalysts 2019, 9(4), 310; https://doi.org/10.3390/catal9040310 - 29 Mar 2019

Cited by 10 | Viewed by 4103

Abstract

The experimentally determined temperature programmed desorption profile of CO from Fe(100) is characterized by four maxima, i.e., α₁-CO, α₂-CO, α₃-CO, and β-CO (see e.g., Moon et al., Surf. Sci. 1985, 163, 215). The CO-TPD profile [...] Read more.

The experimentally determined temperature programmed desorption profile of CO from Fe(100) is characterized by four maxima, i.e., α₁-CO, α₂-CO, α₃-CO, and β-CO (see e.g., Moon et al., Surf. Sci. 1985, 163, 215). The CO-TPD profile is modeled using mean-field techniques and kinetic Monte Carlo to show the importance of lateral interactions in the appearance of the CO-TPD-profile. The inclusion of lateral interactions results in the appearance of a new maximum in the simulated CO-TPD profile if modeled using the mean-field, quasi-chemical approach or kinetic Monte Carlo. It is argued that α₂-CO may thus originate from lateral interactions rather than a differently bound CO on Fe(100). A detailed sensitivity analysis of the effect of the strength of the lateral interactions between the species involved (CO, C, and O), and the choice of the transition state, which affects the activation energy for CO dissociation, and the energy barrier for diffusion on the CO-TPD profile is presented. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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16 pages, 5157 KiB

Open AccessArticle

Approximating Catalyst Effectiveness Factors with Reaction Rate Profiles

by Ville Alopaeus

Catalysts 2019, 9(3), 255; https://doi.org/10.3390/catal9030255 - 13 Mar 2019

Cited by 7 | Viewed by 6959

Abstract

A novel approximate solution for catalyst effectiveness factors is presented. It is based on carefully selected approximate reaction rate profiles, instead of typical assumption of composition profiles inside the catalyst. This formulation allows analytical solution of the approximate model, leading to a very [...] Read more.

A novel approximate solution for catalyst effectiveness factors is presented. It is based on carefully selected approximate reaction rate profiles, instead of typical assumption of composition profiles inside the catalyst. This formulation allows analytical solution of the approximate model, leading to a very simple iterative solution for effectiveness factor for general nonlinear reaction stoichiometry and arbitrary catalyst particle shape. The same model can be used with all practical Thiele modulus values, including multicomponent systems with inert compounds. Furthermore, the correct formulation of the underlying physical model equation is discussed. It is shown that an incorrect but often-used model formulation where convective mass transfer has been neglected may lead to much higher errors than the present approximation. Even with a correctly formulated physical model, rigorous discretization of the catalyst particle volume may have unexpectedly high numerical errors, even exceeding those with the present approximate solution. The proposed approximate solution was tested with a number of examples. The first was an equimolar reaction with first order kinetics, for which analytical solutions are available for the standard catalyst particle geometries (slab, long cylinder, and sphere). Then, the method was tested with a second order reaction in three cases: (1) with one pure reactant, (2) with inert present, and (3) with two reactants and non-stoichiometric surface concentrations. Finally, the method was tested with an industrially relevant catalytic toluene hydrogenation including Maxwell-Stefan formulation for the diffusion fluxes. In all the tested systems, the results were practically identical when compared to the analytical solutions or rigorous finite volume solution of the same problem. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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