Search results for " Kinetic"
showing 10 items of 416 documents
DFT and kinetic evidences of the preferential CO oxidation pattern of manganese dioxide catalysts in hydrogen stream (PROX)
2022
Abstract The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H2 and O2 on a model Mn4O8 cluster. DFT calculations indicate that Mn(IV) atoms prompt an easy CO conversion to CO2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H2 oxidation. Accordingly, a MnCeOx catalyst (Mnat/Ceat, 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T ≥ 293 K and no H2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H2 oxidation rate, al…
Reduction of scouring downstream of a rigid bed by means of a vegetated carpet: experimental investigation in a laboratory flume
2016
Vegetation is a critical component of aquatic ecosystems and exerts an important role in river morphodynamics. This paper describes the results of laboratory study carried out to investigate the role of vegetation on flow field and erosion process developing in non-equilibrium situations. Particular attention is paid to scour evolving downstream of a rigid bed and to the effect of a vegetated carpet used as a protective measure against scouring. The reported experimental study shows that the introduction of the vegetated carpet results in a more favourable configuration than in its absence determining reduced values of flow velocity, turbulence intensity and bed shear stress, and modifying …
Flow Velocity Measurements in Vegetated Channels
2002
Understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes. In this paper the flow over flexible bottom vegetation is experimentally studied. A two-dimensional-acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations, discharges, and flume slopes. The influence of vegetation concentration and the depth/vegetation height ratio on the measured velocity profiles is analyzed. All measured velocity distributions are S-shaped and exhibit a three-zone profile. The relationship between the velocity distribution and the turbulence intensity distribution is also analyzed. The charact…
Hydrothermal liquefaction of wet biomass in batch reactors: Critical assessment of the role of operating parameters as a function of the nature of th…
2022
A scientometric analysis of articles published from 1986 to 2022 on batch hydrothermal liquefaction of microalgae, macroalgae, lignocellulosic biomass, sewage sludge and organic wastes in water was performed. We found that biocrude yield can be correlated with the kinetic severity factor (KSF) and scattering of experimental data increases in the supercritical region probably for uncertainty in the medium density affecting the kinetics of reactions involved in the process. The level of correlation and the yield increased when fast heating rates of the reactor, higher than 25 ◦C/min, were adopted. Energy recovery of biocrude obtained in fast heating experiments changes linearly with biocrude …
Listeria monocytogenes EGD-e biofilms: no mushrooms but a network of knitted chains.
2008
ABSTRACT Listeria monocytogenes is a food pathogen that can attach on most of the surfaces encountered in the food industry. Biofilms are three-dimensional microbial structures that facilitate the persistence of pathogens on surfaces, their resistance toward antimicrobials, and the final contamination of processed goods. So far, little is known about the structural dynamics of L. monocytogenes biofilm formation and its regulation. The aims of this study were, by combining genetics and time-lapse laser-scanning confocal microscopy (LSCM), (i) to characterize the structural dynamics of L. monocytogenes EGD-e sessile growth in two nutritional environments (with or without a nutrient flow), and…
Valorization of rapeseed meal by solid state fermentation for an application in animal nutrition
2017
Solid state fermentation (SSF) is a biotechnological process particularly well adapted to the treatment of vegetable biomass. This technology adjustable to industrial scale, is adapted to current challenges in animal nutrition by developing fermented products in order to improve the quality of raw materials from a nutritional and functional point of view. The work presented in this thesis considers these issues using rapeseed meal from the oil crushing industry.A first screening study highlighted several fungal strains based on their growth performance and protein enrichment (total and digestible) of the substrate. Levels similar to those of soybean meal, the main protein source in animal n…
Development of a modular room-temperature hydride storage system for vehicular applications
2016
The subject of this paper concerns the development of a vehicular hydrogen tank system, using a commercial interstitial metal hydride as storage material. The design of the tank was intended to feed a fuel cell in a light prototype vehicle, and the chosen hydride material, Hydralloy C5 by GfE, was expected to be able to absorb and desorb hydrogen in a range of pressure suitable for this purpose. A systematic analysis of the material in laboratory scale allows an extrapolation of the thermodynamic and reaction kinetics data. The following development of the modular tank was done according to the requirements of the prototype vehicle propulsion system and led to promising intermediate results…
Organocatalytic Enantioselective Synthesis of α-Hydroxyketones through a Friedel−Crafts Reaction of Naphthols and Activated Phenols with Aryl- and Al…
2016
[EN] An efficient organocatalytic asymmetric synthesis of alpha-hydroxyketones has been developed. Quinine-derived thiourea catalyzed the enantioselective Friedel Crafts alkylation of naphthols and activated phenols with aryl- and alkylglyoxal hydrates, providing the corresponding chiral alpha-hydroxyketones with high yields (up to 97%) and excellent enantioselectivities (up to 99% ee).
A DFT mechanistic study of the synthesis of trans-Z,Z-[PtIICl(NH3){HN = C(NH2)Me}2]Cl from addition of NH3 to trans-[PtIICl2(N CMe)2]
2020
Abstract The reaction mechanism between trans-[PtIICl2(N CMe)2] and ammonia to give trans-Z,Z-[PtIICl(NH3){HN = C(NH2)Me}2]Cl has been studied at DFT level. Results showed that, in dichloromethane solution at 263.15 K, the chloride substitution by the ammonia on platinum is a process kinetically more favoured than the ammonia nucleophilic addition to the nitrile of about three orders of magnitude, and hence the nucleophilic addition reaction occurs after. Finally, both nucleophilic addition steps are geometrically driven to give products in the E configuration even if the final products were experimentally observed in the Z configuration. For trans-Z,Z-[PtIICl(NH3)(N CMe)2, the isomerizatio…
Ordering kinetics in synthetic Mg(Al,Fe3+)2O4 spinels: Quantitative elucidation of the whole Al-Mg-Fe partitioning, rate constants, activation energi…
2014
A novel procedure, based on the application of the kinetics simulator Gepasi, has been successfully applied for modeling the cation ordering process in two synthetic Mg(Al2-yFe3+y)O4 spinels (y~ 0.39 and 0.54, samples F39 and F54, respectively). The kinetic profiles suggested a two-stage mechanism, with rapid inter-site exchange of Fe3+ with Mg followed by slow exchange of Al with Mg. The trial to apply the classical approaches, based on the explicit solutions of the differential equations corresponding to single-cation (Sha-Chappel model) or two-cation (Müller model) exchange reactions, proved not feasible in the whole time range, thus implying a lack of information about the exchange proc…