Open-cell foams as catalysts support : a systematic analysis of the mass transfer limitations
TL;DR: In this paper, the influence of local hydrodynamic effects on the diffusion-reaction phenomena occurring at the gas-solid interface of the open-cell solid foams is investigated by Direct Numerical Simulations assuming an infinitely fast reaction.
About: This article is published in Chemical Engineering Journal.The article was published on 2020-08-01 and is currently open access. It has received 31 citations till now. The article focuses on the topics: Thiele modulus & Mass transfer.
Citations
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TL;DR: In this paper, the effect of 3 ¼wt% PdO on Co3O4 coated on three different OCFs (alumina, silicon carbide and zirconia) was investigated toward the reaction of CH4 combustion in lean conditions.
22 citations
TL;DR: The formulated correlations in catalytically activated periodic open cellular structures are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.
Abstract: In this work, we investigate the gas-solid heat and mass transfer in catalytically activated periodic open cellular structures, which are considered a promising solution for intensification of catalytic processes limited by external transport, aiming at the derivation of suitable correlations. Computational fluid dynamics is employed to investigate the Tetrakaidekahedral and Diamond lattice structures. The influence of the morphological features and flow conditions on the external transport properties is assessed. The strut diameter is an adequate characteristic length for the formulation of heat and mass transfer correlations; accordingly, a power-law dependence of the Sherwood number to the Reynolds number between 0.33 and 0.67 was found according to the flow regimes in the range 1-128 of the Reynolds number. An additional -1.5-order dependence on the porosity is found. The formulated correlations are in good agreement with the simulation results and allow for the accurate evaluation of the external transfer coefficients for POCS.
20 citations
TL;DR: In this paper, a modified diffusional model incorporating temperature-dependent moisture diffusivity (Deff) could simulate the apple drying process well, and the drying time was found to be reduced by 1.5-68.9% compared with air drying without any pretreatment and sonication.
Abstract: Pretreatments of either water blanching or NaCl immersion and airborne ultrasound-assisted air drying were combined to dehydrate apple slices. The drying time was found to be reduced by 1.5–68.9% compared with air drying without any pretreatment and sonication. Meanwhile, it was found that sequential water blanching coupled with air drying with sonication gave the shortest drying time. A modified diffusional model incorporating temperature-dependent moisture diffusivity (Deff) could simulate the apple drying process well. Water blanching pretreatment and airborne sonication were found to lower the activation energy required for the enhancement of moisture diffusive ability, and intensified water exchange on apple surface to speed up the drying process. Both water blanching and NaCl immersion significantly increased the amounts of procyanidin B2 in dehydrated apple slices. However, airborne sonication promoted the loss of procyanidin B2 in apple slices with pretreatments during air drying. In addition, sonication had no obvious influences on apple PPO activity and individual organic acids throughout drying. Overall, the sequential NaCl immersion pretreatment (or water blanching pretreatment) and drying with airborne sonication are effective to improve the quality of dried apple slices.
16 citations
TL;DR: In this article, the external mass transfer properties of 3D printed catalyst supports were evaluated using a 3D printer with a resin characterized by a high heat deflection temperature (HDT) for the manufacturing of samples at a lower price and with higher accuracy than equivalent metallic structures.
11 citations
TL;DR: In this article, the kinetic and mass transfer resistances (pore and interphase diffusion) were evaluated by varying the Co3O4 amount in the catalyst supported on the zirconia open cell foam (Zir-OCF) of 30 ppi.
10 citations
References
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TL;DR: In this article, a quantitative analysis of particle to fluid heat transfer on the basis of a stochastic model of the fixed bed leads to a constant value of the Nusselt group at low Reynolds number.
933 citations
"Open-cell foams as catalysts suppor..." refers methods in this paper
...Equation 12 may be compared against a more conventional one, such as the Gunn [40] correlation which was proposed for spherical particle systems....
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...In the dilute limit, the Gunn correlation shows a strong dependency with the Reynolds number with a scaling of 0.7 indicating that mass transfer is significantly enhanced when the flow-rate is increased....
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TL;DR: The data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size.
Abstract: Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption−desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1−20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O−18O2−16O2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of r...
428 citations
"Open-cell foams as catalysts suppor..." refers background in this paper
...It presents a negative reaction order with respect to CO for high CO coverages [36,37]:...
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TL;DR: In this paper, open-celled metal foams have been characterized as supports for structured catalysts, considering their utilization in gas−solid catalytic processes with short contact times and high reaction rates, typically controlled by gas-solid diffusional mass transport.
Abstract: Open-celled metal foams have been characterized as supports for structured catalysts, considering their utilization in gas−solid catalytic processes with short contact times and high reaction rates, typically controlled by gas−solid diffusional mass transport Examples of such processes are found in the field of environmental catalysis, including, eg, catalytic combustion, selective catalytic reduction (SCR-DeNOx), and automotive exhaust gas after treatment In this work, foams with different cell sizes were coated with a thin layer of palladium−alumina and tested in a 9-mm inner diameter tubular reactor by performing the catalytic oxidation of CO at empty tube velocities in the range of 08−26 m/s The coated foams exhibited sufficient catalytic activity to achieve mass-transfer-limited operation in the temperature range of 300−450 °C Under such conditions, mass-transfer coefficients were determined according to a simple one-dimensional model of the test reactor Adopting the average diameter of the
341 citations
"Open-cell foams as catalysts suppor..." refers background or methods in this paper
...[12] characterized the mass transfer in a Pd/Al2O3 wash-coated metal foams during the CO oxidation and obtained a dimensionless correlation for mass transfer coefficients which closely resembles semi-theoretical correlations....
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...[12,13] are above the line of full mass-transfer limitations, and some points are just below the line....
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...The correlations for the Sherwood number as function of the Reynolds reported in bibliography [12,13] and obtained in this work follow Eq....
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TL;DR: In this paper, the boundary condition at the surface of the particles at the level of the discrete momentum and thermal energy equations of the fluid is incorporated with a second-order method.
207 citations
TL;DR: In this article, a combination of microscopic imaging, mercury porosimetry and magnetic resonance imaging allowed the determination of the pore sizes, strut diameters, void fractions and geometric surface areas of the foams.
206 citations
"Open-cell foams as catalysts suppor..." refers methods in this paper
...[2,14] studied the mass transfer and the pressure drop of alumina foams, by performing the CO oxidation on Pt/SnO2 and proposed correlations for the mass transfer coefficient as function of dimensionless numbers and geometrical factors of the foams....
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