scholarly journals Plasma Catalysis: Distinguishing between Thermal and Chemical Effects

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 185 ◽  
Author(s):  
Guido Giammaria ◽  
Gerard van Rooij ◽  
Leon Lefferts

The goal of this study is to develop a method to distinguish between plasma chemistry and thermal effects in a Dielectric Barrier Discharge nonequilibrium plasma containing a packed bed of porous particles. Decomposition of CaCO3 in Ar plasma is used as a model reaction and CaCO3 samples were prepared with different external surface area, via the particle size, as well as with different internal surface area, via pore morphology. Also, the effect of the CO2 in gas phase on the formation of products during plasma enhanced decomposition is measured. The internal surface area is not exposed to plasma and relates to thermal effect only, whereas both plasma and thermal effects occur at the external surface area. Decomposition rates were in our case found to be influenced by internal surface changes only and thermal decomposition is concluded to dominate. This is further supported by the slow response in the CO2 concentration at a timescale of typically 1 minute upon changes in discharge power. The thermal effect is estimated based on the kinetics of the CaCO3 decomposition, resulting in a temperature increase within 80 °C for plasma power from 0 to 6 W. In contrast, CO2 dissociation to CO and O2 is controlled by plasma chemistry as this reaction is thermodynamically impossible without plasma, in agreement with fast response within a few seconds of the CO concentration when changing plasma power. CO forms exclusively via consecutive dissociation of CO2 in the gas phase and not directly from CaCO3. In ongoing work, this methodology is used to distinguish between thermal effects and plasma–chemical effects in more reactive plasma, containing, e.g., H2.

2007 ◽  
Vol 7 (11) ◽  
pp. 3959-3963 ◽  
Author(s):  
Sung June Cho ◽  
Young-Kwon Park ◽  
Jong-Ki Jeon ◽  
Young Soo Ko ◽  
Jin-Heong Yim ◽  
...  

Nanoporous zeolite MFI was prepared by using HClO4 as a promoter. A significant proportion of the synthesized zeolite MFI nanoparticles exhibited nanoporous characteristics. Although the synthesis of the zeolite MFI was completed within 6 h, the crystallinity of all the zeolite MFI was shown to be high. The synthesis time of approximately 6 h used in this study was much shorter than the conventional hydrothermal method. The feasibility of the new nanoporous zeolite MFI towards the gas phase catalytic oxidation of a model for dioxin, 1,2-dichlorobenzene, was tested by comparing the catalytic activity of Pt/nanoporous zeolite MFI with that of a Pt/γ-Al2O3 catalyst. The catalytic activity of the Pt/nanoporous zeolite MFI was higher than that of the Pt/γ-Al2O3 catalyst. The internal surface area and acidity appears to be a major factor for the decomposition of 1,2-dichlorobenzene.


Clay Minerals ◽  
1989 ◽  
Vol 24 (4) ◽  
pp. 631-647 ◽  
Author(s):  
R. Malberg ◽  
I. Dékány ◽  
G. Lagaly

AbstractShort-chain alkylammonium derivatives of montmorillonite (< 8 or 10 C atoms in the alkyl chain) adsorb alcohols in the micropores between the alkylammonium ions. The external surface area and the micropore volume are derived from comparison plots of ethanol and butanol adsorption isotherms. The micropore volume varies between ∼0 (decylammonium derivative) and 100µl/g (methylammonium derivative); the external surface area determined by ethanol and butanol gas adsorption is about 50 m2/g, and is almost independent of the alkyl chain length. In contact with the alcohols, the alkylammonium ions in the interlayer space remain in h1 or h2 arrangement (monolayers or bilayers of flat-lying alkylammonium ions); on the external surface they move into an upward position. The heat of immersion decreases strongly with increasing alkyl chain length to a minimum for decylammonium ions, the variation being very similar for ethanol, butanol, hexanol, octanol and decanol. Immersion in ethanol increases the external surface area at the expense of the internal surface area. In butanol and longer alcohols this area remains unchanged. The increase of the external surface is related mainly to changes in the less ordered regions around the core of the crystals which consists of coherent silicate layers. The heat of wetting is ∼ 110 mJ/m2 (external and internal surfaces). The integral enthalpy of adsorption of butanol, 40–50 kJ/mol, is independent of the alkyl chain length (nc ≤ 8).


Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 964
Author(s):  
Thomas Steiner ◽  
Daniel Neurauter ◽  
Peer Moewius ◽  
Christoph Pfeifer ◽  
Verena Schallhart ◽  
...  

This study investigates geometric parameters of commercially available or recently published models of catalyst substrates for passenger vehicles and provides a numerical evaluation of their influence on heat-up behavior. Parameters considered to have a significant impact on the thermal economy of a monolith are: internal surface area, heat transfer coefficient, and mass of the converter, as well as its heat capacity. During simulation experiments, it could be determined that the primary role is played by the mass of the monolith and its internal surface area, while the heat transfer coefficient only has a secondary role. Furthermore, an optimization loop was implemented, whereby the internal surface area of a commonly used substrate was chosen as a reference. The lengths of the thin wall and high cell density monoliths investigated were adapted consecutively to obtain the reference internal surface area. The results obtained by this optimization process contribute to improving the heat-up performance while simultaneously reducing the valuable installation space required.


2017 ◽  
Vol 64 (3-4) ◽  
pp. 155-162
Author(s):  
Aleksandra Gorączko ◽  
Andrzej Olchawa

AbstractThe paper presents results of a study on the amount of water associated with the solid phase of the clay water system at the plastic limit. Two model monomineral clays, namely kaolinite, and montmorillonite, were used in the study. The latter was obtained by gravitational sedimentation of Na-bentonite (Wyoming).The calculated mean number of water molecule layers on the external surface of montmorillonite was 14.4, and water in interlayer spaces constituted 0.3 of the water mass at the plastic limit.The number of water layers on the external surface of kaolinite particles was 63, which was related to the higher density of the surface electrical charge of kaolinite compared to that of montmorillonite.The calculations were made on the basis of the external surface area of clays and the basal spacing at the plastic limit measured by an X-ray diffraction test. The external surface area of clays was estimated by measuring sorption at a relative humidity p/p0 = 0.5.


2004 ◽  
Vol 67 (5) ◽  
pp. 1017-1021 ◽  
Author(s):  
JOHN B. LUCHANSKY ◽  
JEFFREY E. CALL

Commercially prepared frankfurters were formulated with and without ~1.4% potassium lactate and 0.1% sodium diacetate and were subsequently processed in cellulose casings coated with and without nisin (~50,000 IU per square inch of internal surface area) to control the outgrowth of Listeria monocytogenes during refrigerated storage. The frankfurters were inoculated with ~5 log CFU per package of a five-strain mixture of L. monocytogenes and then vacuum sealed before being stored at 4° C for 60 to 90 days. Surviving organisms were recovered and enumerated by rinsing each package with 18 ml of sterile 0.1% peptone water and plating onto MOX selective agar. The data for each of two trials were averaged. In packages that contained frankfurters formulated with potassium lactate and sodium diacetate and prepared in nisin-coated casings, L. monocytogenes levels decreased by 1.15 log CFU per package after 90 days of storage. L. monocytogenes levels decreased by 0.95 log CFU per package in frankfurters that were prepared in casings that were not coated with nisin. In packages of frankfurters that were formulated without potassium lactate and sodium diacetate and prepared in nisin-coated casings, L. monocytogenes levels decreased by 0.88 log CFU per package after 15 days of storage but then increased appreciablythereafter over a 60-day period of refrigerated storage. There was also an appreciable increase in pathogen numbers during 60 days of storage in otherwise similar frankfurters formulated without potassium lactate and sodium diacetate prepared in casings that were not coated with nisin. These data confirm that potassium lactate and sodium diacetate display listeriostatic activity as an ingredient of commercial frankfurters. These data also establish that cellulose casings coated with nisin display only moderate antilisterial activity in vacuum-sealed packages of commercially prepared frankfurters during storage at 4° C.


2004 ◽  
Vol 277 (2) ◽  
pp. 383-386 ◽  
Author(s):  
Ricardo Navarrete ◽  
Philip Llewellyn ◽  
Françoise Rouquerol ◽  
Renaud Denoyel ◽  
Jean Rouquerol

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