scholarly journals A First Principle Comparative Study on Chemisorption of H2on C60, C80, and Sc3N@C80in Gas Phase and Chemisorption of H2on Solid Phase C60

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Hongtao Wang ◽  
Lijuan Chen ◽  
Yongkang Lv ◽  
Jianwen Liu ◽  
Gang Feng
Keyword(s):  
High Pressure ◽  
Gas Phase ◽  
Active Sites ◽  
Adsorption Process ◽  
Reaction Path ◽  
Solid Phase ◽  
Dissociative Adsorption ◽  
Chain Reaction ◽  
A Chain ◽  
Initial Adsorption

The chemisorptions of H2on fullerenes C60and C80, endofullerene Sc3C@C80and solid C60were comparatively studied. A chain reaction mechanism for dissociative adsorption of H2on solid C60is proposed under high pressure. The breaking of H–H bond is concerted with the formation of two C–H bonds on two adjacent C60in solid phase. The adsorption process is facilitated by the application of high pressure. The initial H2adsorption on two adjacent C60gives a much lower barrier 1.36 eV in comparison with the barrier of adsorption on a single C60(about 3.0 eV). As the stereo conjugate aromaticity of C60is destructed by the initial adsorption, some active sites are created. Hence the successive adsorption becomes easier with much low barriers (0.6 eV). In addition, further adsorption can create new active sites for the next adsorption. Thus, a chain reaction path is formed with the initial adsorption dominating the whole adsorption process.

Oxydation lente du cétène en phase gazeuse. I. Réaction à "hautes températures"

1971 ◽  
Vol 49 (2) ◽  
pp. 294-302 ◽  
Author(s):  
Pierre Michaud ◽  
Cyrias Ouellet
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Gas Phase ◽  
Static Method ◽  
Chain Reaction ◽  
Slow Combustion ◽  
Temperature Ranges ◽  
Higher Temperature ◽  
A Chain ◽  
Two Temperature

The slow combustion of ketene in the gas phase was studied by the static method in a 30 × 4 cm Vycor cylinder between 280 and 500 °C at pressures above 20 mm Hg. Extending the work of Barnard and Kirschner, we have established the existence of two types of slow combustion of ketene corresponding to two temperature ranges. In this first paper, we describe the kinetic and analytical results obtained in the higher temperature range (380–500 °C). The reaction is autocatalytic and shows a low temperature coefficient corresponding to a few kilocalories per mole. The main products are carbon monoxide, formaldehyde, water, and carbon dioxide. No ethylene was detected. We suggest a chain reaction in which formaldehyde is the intermediate responsible for degenerate branching:[Formula: see text]

Reaction of Hydrogen Atoms with Carbon Suboxide

1971 ◽  
Vol 49 (5) ◽  
pp. 803-806 ◽  
Author(s):  
Nick Demchuk ◽  
H. D. Gesser
Keyword(s):  
Gas Phase ◽  
Intermediate Formation ◽  
Phase Reaction ◽  
Hydrogen Atoms ◽  
Chain Reaction ◽  
Carbon Suboxide ◽  
Formyl Radical ◽  
Gas Phase Reaction ◽  
Temperature Range ◽  
A Chain

The gas phase reaction of hydrogen atoms with carbon suboxide was studied over the temperature range of−96 to 235 °C and was found to proceed via a chain reaction. The products found were CH4, CO, CH2CO, C2H6, (CHO)2, and polymer. A mechanism is proposed and the chain reaction is explained by the intermediate formation of ketene and the formyl radical.

scholarly journals The combination of hydrogen and oxygen photosensitised by nitrogen peroxide

1933 ◽  
Vol 139 (837) ◽  
pp. 147-162 ◽  
Keyword(s):  
Hydrogen Peroxide ◽  
Spectroscopic Study ◽  
Gas Phase ◽  
Alternative Form ◽  
Chain Mechanism ◽  
Homogeneous Reaction ◽  
Chain Reaction ◽  
Chain Reactions ◽  
Temperature And Pressure ◽  
A Chain

The homogeneous reaction between hydrogen and oxygen has been proved by the work of Hinshelwood, of Haber, and of Semenoff to be a chain reaction, which under certain conditions of temperature and pressure may pass over into an explosive combination. The reaction is subject to the kinetics characteristic of certain types of chain reactions, in that, for any particular temperature, there are upper and lower pressure limits for explosion, the former controlled by deactivation of the chains in the gas phase, and the latter by their termination at the surface. The conditions further point to a branching chain mechanism; below 300°C. there is no observable propagation of reaction chains. These facts seem to be well represented by the scheme of Bonhoeffer and Haber, which was put forward on the basis of a spectroscopic study of the dissociation of steam at high temperatures. H + H 2 + O 2 = HO + H 2 O + 102,000 cals. (1) HO + H 2 = H 2 O + H + 10,000 cals. (2) reaction (1) sometimes taking the alternative form H + H 2 + O 2 = OH + OH + H - 2000 cals. (1a) which accounts for the branching of the chains. Reaction (2) does not occur appreciably at temperatures below 300°C., but the OH radicles yield hydrogen peroxide which may be detected.

scholarly journals The combination of hydrogen and oxygen on the surface of silica and its relation to the propagation of reaction chains in the gas

1931 ◽  
Vol 134 (823) ◽  
pp. 1-7 ◽  
Keyword(s):  
Gas Phase ◽  
Surface Reaction ◽  
Silica Surface ◽  
Chain Reaction ◽  
First Order ◽  
Slow Reaction ◽  
Upper Limit ◽  
A Chain ◽  
Reaction Vessels

The combination of hydrogen and oxygen, at temperatures between 400° and 600°C. in vessels of porcelain or silica involves several different processes. At the lower temperatures a surface reaction tends to predominate, which on a silica surface is approximately of the first order. At higher temperatures and higher pressures a chain reaction occurs in the gas phase. At temperatures greater than 450° C. there also exists a lower and an upper limit of pressure below and above which reaction is slow and between which explosion occurs.The transition from slow reaction to explosion is an abrupt one, the limits representing discontinuities of some kind. The upper limit is almost the same in reaction vessels of silica or porcelain and is nearly independent of their dimensions.

Observations on a Relationship between Steroid Metabolism and the Concentration of Plasma Fibrinogen

1963 ◽  
Vol 10 (02) ◽  
pp. 400-405 ◽  
Author(s):  
B. A Amundson ◽  
L. O Pilgeram
Keyword(s):  
Blood Coagulation ◽  
Methyl Ether ◽  
Broad Spectrum ◽  
Human Subjects ◽  
Plasma Fibrinogen ◽  
Steroid Metabolism ◽  
Specific Site ◽  
Chain Reaction ◽  
Normal Human ◽  
A Chain

SummaryEnovid (5 mg norethynodrel and 0.075 mg ethynylestradiol-3-methyl ether) therapy in young normal human subjects causes an increase in plasma fibrinogen of 32.4% (P >C 0.001). Consideration of this effect together with other effects of Enovid on the activity of specific blood coagulatory factors suggests that the steroids are exerting their effect at a specific site of the blood coagulation and/or fibrinolytic system. The broad spectrum of changes which are induced by the steroids may be attributed to a combination of a chain reaction and feed-back control.

scholarly journals Study of deactivation in mesocellular foam carbon (MCF-C) catalyst used in gas-phase dehydrogenation of ethanol

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yoottapong Klinthongchai ◽  
Seeroong Prichanont ◽  
Piyasan Praserthdam ◽  
Bunjerd Jongsomjit
Keyword(s):  
Catalytic Activity ◽  
Pore Size ◽  
Gas Phase ◽  
Surface Area ◽  
Active Sites ◽  
Operating Temperature ◽  
Coke Formation ◽  
Ethanol Conversion ◽  
Deactivation Of Catalyst ◽  
Dehydrogenation Of Ethanol

AbstractMesocellular foam carbon (MCF-C) is one the captivating materials for using in gas phase dehydrogenation of ethanol. Extraordinary, enlarge pore size, high surface area, high acidity, and spherical shape with interconnected pore for high diffusion. In contrary, the occurrence of the coke is a majority causes for inhibiting the active sites on catalyst surface. Thus, this study aims to investigate the occurrence of the coke to optimize the higher catalytic activity, and also to avoid the coke formation. The MCF-C was synthesized and investigated using various techniques. MCF-C was spent in gas-phase dehydrogenation of ethanol under mild conditions. The deactivation of catalyst was investigated toward different conditions. Effects of reaction condition including different reaction temperatures of 300, 350, and 400 °C on the deactivation behaviors were determined. The results indicated that the operating temperature at 400 °C significantly retained the lowest change of ethanol conversion, which favored in the higher temperature. After running reaction, the physical properties as pore size, surface area, and pore volume of spent catalysts were decreased owing to the coke formation, which possibly blocked the pore that directly affected to the difficult diffusion of reactant and caused to be lower in catalytic activity. Furthermore, a slight decrease in either acidity or basicity was observed owing to consumption of reactant at surface of catalyst or chemical change on surface caused by coke formation. Therefore, it can remarkably choose the suitable operating temperature to avoid deactivation of catalyst, and then optimize the ethanol conversion or yield of acetaldehyde.

scholarly journals CO Oxidation Efficiency and Hysteresis Behavior over Mesoporous Pd/SiO2 Catalyst

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 131 ◽  
Author(s):  
Rola Mohammad Al Soubaihi ◽  
Khaled Mohammad Saoud ◽  
Myo Tay Zar Myint ◽  
Mats A. Göthelid ◽  
Joydeep Dutta
Keyword(s):  
Carbon Monoxide ◽  
Catalytic Activity ◽  
Co Oxidation ◽  
Active Sites ◽  
Bond Activation ◽  
Dissociative Adsorption ◽  
High Catalytic Activity ◽  
Good Catalytic Activity ◽  
Pretreatment Conditions ◽  
Oxidation Efficiency

Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO2 catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (Tig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than Tig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO2 catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at Tig to form CO2. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO2 support interaction, and PdO formation and decomposition.

scholarly journals Synergistic Effect of Alkali Na and K Promoter on Fe-Co-Cu-Al Catalysts for CO2 Hydrogenation to Light Hydrocarbons

Catalysts ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 735
Author(s):  
Yuhao Zheng ◽  
Chenghua Xu ◽  
Xia Zhang ◽  
Qiong Wu ◽  
Jie Liu
Keyword(s):  
Synergistic Effect ◽  
Active Sites ◽  
Intermediate Formation ◽  
Active Phase ◽  
Dissociative Adsorption ◽  
Co2 Hydrogenation ◽  
Chain Growth ◽  
Co2 Conversion ◽  
Light Hydrocarbons ◽  
Active Centers

Alkali metal K- and/or Na-promoted FeCoCuAl catalysts were synthesized by precipitation and impregnation, and their physicochemical and catalytic performance for CO2 hydrogenation to light hydrocarbons was also investigated in the present work. The results indicate that Na and/or K introduction leads to the formation of active phase metallic Fe and Fe-Co crystals in the order Na < K < K-Na. The simultaneous introduction of Na and K causes a synergistic effect on increasing the basicity and electron-rich property, promoting the formation of active sites Fe@Cu and Fe-Co@Cu with Cu0 as a crystal core. These effects are advantageous to H2 dissociative adsorption and CO2 activation, giving a high CO2 conversion with hydrogenation. Moreover, electron-rich Fe@Cu (110) and Fe-Co@Cu (200) provide active centers for further H2 dissociative adsorption and O-C-Fe intermediate formation after adsorption of CO produced by RWGS. It is beneficial for carbon chain growth in C2+ hydrocarbons, including olefins and alkanes. FeCoCuAl simultaneously modified by K-Na exhibits the highest CO2 conversion and C2+ selectivity of 52.87 mol% and 89.70 mol%, respectively.

scholarly journals Pathogenesis and Management of COVID-19

2021 ◽  
Vol 11 (2) ◽  
pp. 77-93
Author(s):  
Khalid O. Alfarouk ◽  
Sari T. S. AlHoufie ◽  
Samrein B. M. Ahmed ◽  
Mona Shabana ◽  
Ahmed Ahmed ◽  
...  
Keyword(s):  
Multiple Organ Failure ◽  
Human Body ◽  
Inflammatory Mediators ◽  
Expression Patterns ◽  
Multiple Organ ◽  
Cytokine Storm ◽  
Chain Reaction ◽  
Road Map ◽  
A Chain ◽  
Global War

COVID-19, occurring due to SARS-COV-2 infection, is the most recent pandemic disease that has led to three million deaths at the time of writing. A great deal of effort has been directed towards altering the virus trajectory and/or managing the interactions of the virus with its subsequent targets in the human body; these interactions can lead to a chain reaction-like state manifested by a cytokine storm and progress to multiple organ failure. During cytokine storms the ratio of pro-inflammatory to anti-inflammatory mediators is generally increased, which contributes to the instigation of hyper-inflammation and confers advantages to the virus. Because cytokine expression patterns fluctuate from one person to another and even within the same person from one time to another, we suggest a road map of COVID-19 management using an individual approach instead of focusing on the blockbuster process (one treatment for most people, if not all). Here, we highlight the biology of the virus, study the interaction between the virus and humans, and present potential pharmacological and non-pharmacological modulators that might contribute to the global war against SARS-COV-2. We suggest an algorithmic roadmap to manage COVID-19.

Influence of initiation mode on stability and control of a chain reaction

1980 ◽  
Vol 20 (18) ◽  
pp. 1197-1204 ◽  
Author(s):  
H. T. Chen ◽  
P. A. Chartier ◽  
S. Setthachayanon
Keyword(s):  
Chain Reaction ◽  
Stability And Control ◽  
A Chain ◽  
And Control
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