Experimental and theoretical velocity profiles for pure rotational scattering in carbon dioxide-hot hydrogen atom collisions

1995 ◽  
Vol 99 (19) ◽  
pp. 7381-7387 ◽  
Author(s):  
C. K. Ni ◽  
T. G. Kreutz ◽  
G. W. Flynn
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
Velocity Profiles

The water–boryl radical as a proton-coupled electron transfer reagent for carbon dioxide, formic acid, and formaldehyde — Theoretical approach

2013 ◽  
Vol 91 (2) ◽  
pp. 155-168
Author(s):  
Waled Tantawy ◽  
Ahmed Hashem ◽  
Nabil Yousif ◽  
Eman Flefel
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Bond ◽  
Electron Transfer ◽  
Hydrogen Atom ◽  
Transfer Process ◽  
Carbonyl Compounds ◽  
Hydrogen Atom Transfer ◽  
Transfer Reactions ◽  
Atom Transfer ◽  
Proton Coupled Electron Transfer

The thermochemistry of the hydrogen atom transfer reactions from the H2O–BX2 radical system (X = H, CH3, NH2, OH, F) to carbon dioxide, formic acid, and (or) formaldehyde, which produce hydroxyformyl, dihydroxymethyl, and hydroxymethyl radicals, respectively, were investigated theoretically at ROMP2/6–311+G(3DF,2P)//UB3LYP/6–31G(D) and UG3(MP2)-RAD levels of theory. Surprisingly, in the cases of a strong Lewis acid (X = H, CH3, F), the spin transfer process from the water–boryl radical to the carbonyl compounds was barrier-free and associated with a dramatic reduction in the B–H bond dissociation energy (BDE) relative to that of isolated water–borane complexes. Examining the coordinates of these reactions revealed that the entire hydrogen atom transfer process is governed by the proton-coupled electron transfer (PCET) mechanism. Hence, the elucidated mechanism has been applied in the cases of weak Lewis acids (X = NH2, OH), and the variation in the accompanied activation energy was attributed to the stereoelectronic effect interplaying in CO2 and HCOOH compared with HCHO. We ascribed the overall mechanism as a SA-induced five-center cyclic PCET, in which the proton transfers across the so-called complexation-induced hydrogen bond (CIHB) channel, while the SOMOB–LUMOC=O′ interaction is responsible for the electron migration process. Owing to previous reports that interrelate the hydrogen-bonding and the rate of proton-coupled electron-transfer reactions, we postulated that “the rate of the PCET reaction is expected to be promoted by the covalency of the hydrogen bond, and any factor that enhances this covalency could be considered an activator of the PCET process.” This postulate could be considered a good rationale for the lack of a barrier associated with the hydrogen atom transfer from the water-boryl radical system to the carbonyl compounds. Light has been shed on the water–boryl radical reagent from the thermodynamic perspective.

Vacuum ultra-violet flash photolysis of water vapour

1962 ◽  
Vol 266 (1325) ◽  
pp. 185-197 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
Complex Formation ◽  
Hydroxyl Radical ◽  
Water Vapour ◽  
Iodine Atom ◽  
Flash Photolysis ◽  
Ultra Violet ◽  
Kinetics Of ◽  
Vacuum Ultra Violet

An apparatus for effecting flash photolysis in the vacuum ultra-violet region is described. Appreciable decompositions of water, carbon dioxide, acetylene, ethylene and methane were effected with a 2000 J flash of 30 p .s duration. A detailed study of water vapour photolysis has established that, in the primary step, at least 90 % of the dissociation leads to a hydrogen atom and a hydroxyl radical. The kinetics of the hydroxyl radical disappearance, following flash photolysis of water vapour in the presence of various third bodies, has been studied. The rate constant is faster in xenon than in helium and other similarities with the data on iodine atom recombination suggest the operation of a mechanism involving intermediate complex formation.

scholarly journals Kinetic study of carbon dioxide catalytic methanation over cobalt–nickel catalysts

2019 ◽  
Vol 7 (1) ◽  
pp. 74-80 ◽  
Author(s):  
Alla G. Dyachenko ◽  
Olena V. Ischenko ◽  
Snizhana V. Gaidai ◽  
Tetiana M. Zakharova ◽  
Andrii V. Yatsymyrskyi ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
High Stability ◽  
Spectroscopic Analysis ◽  
Kinetic Equations ◽  
Nickel Catalysts ◽  
Carbon Dioxide Molecule ◽  
Cobalt Nickel ◽  
Limiting Step ◽  
Good Agreement

Based on the data of the thermoprogrammed desorption and using mass-spectroscopic analysis of desorbed products and on the kinetic patterns of the methanation process for cobalt–nickel catalysts, we suggested a mechanism for the reaction which passes through forming intermediate formyl compounds: CHO*, HCOH*, and HCOOH*. Because of the high stability of the carbon dioxide molecule, the step of adding the first hydrogen atom is the limiting step. Such a mechanism is in good agreement with the proposed kinetic equations.

Experimental and theoretical velocity profiles for pure rotational scattering: CO–hot hydrogen atom collisions

1994 ◽  
Vol 101 (11) ◽  
pp. 9499-9505 ◽  
Author(s):  
Chi‐Kung Ni ◽  
George W. Flynn ◽  
Sheldon Green
Keyword(s):  
Hydrogen Atom ◽  
Velocity Profiles

scholarly journals The mechanism of the steam-carbon reaction

1948 ◽  
Vol 193 (1034) ◽  
pp. 377-399 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Hydrogen Atom ◽  
Active Carbon ◽  
Active Sites ◽  
Adsorbed Oxygen ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Exponential Factor ◽  
Gaseous Carbon Monoxide

The detailed mechanism of the reaction between steam and coconut shell charcoal has been studied by the method described in the preceding paper. The temperature has been varied in the range 680 to 800° C and the pressures of the gases from 10 to 760 mm. Steam first reacts with the carbon to give oxygen and hydrogen atoms separately adsorbed on neighbouring sites. An initial dissociation into an adsorbed hydrogen atom and an adsorbed hydroxyl radical is probably followed by the more rapid transfer of the second hydrogen atom to the carbon. Only about 2% of the total surface takes part in the reaction; these sites are distinct from the smaller group which reacts with carbon dioxide, but they are also thought to be atoms at the edges of lattice planes. The rate of the first stage can be accounted for by assuming that reaction occurs in those collisions in which the combined energy of the incident steam molecule and the two active carbon atoms exceeds 75 kcal. Adsorbed hydrogen evaporates rapidly, but in the steady state much remains on the surface. A close correlation has been observed between the fraction of the active sites occupied by hydrogen and the extent to which the reaction is retarded by that gas. Adsorbed oxygen reacts much more slowly to form gaseous carbon monoxide; the latter, which has no retarding effect, is not appreciably adsorbed by the sites accessible to steam. The activation energy for the conversion of an adsorbed oxygen atom into gaseous carbon monoxide is found to be 55 kcal., and the non- exponential factor to be 10 11±1.7 sec. -1 which may be compared with the value of 10 13 sec. -1 predicted by simple theory. As the active carbon atoms are thought to be exerting less than their maximum valency, it is suggested that the two types differ in the number of extra bonds which they can form. Energetic considerations show that whereas those which can form a single bond should react with steam, only the relatively few capable of forming a double bond should react with carbon dioxide. This theory also explains why hydrogen is strongly adsorbed by both the steam and the carbon dioxide sites, but carbon monoxide only by the latter type. The relation of these views to outstanding problems of the oxygen-carbon and nitrous oxide-carbon reactions is discussed, and an explanation of the main kinetic features of those processes is given.

Axial Development of Unusual Velocity Profiles due to Heat Transfer in Variable Density Fluids

1980 ◽  
Vol 102 (1) ◽  
pp. 71-74 ◽  
Author(s):  
E. G. Hauptmann ◽  
A. Malhotra
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Velocity Profiles ◽  
Variable Density ◽  
Equation Model ◽  
Two Dimensional ◽  
Circular Duct ◽  
Axis Of Symmetry ◽  
Axial Development

Velocity profiles exhibiting maxima away from the axis of symmetry have been calculated for supercritical carbon dioxide flowing vertically in a heated circular duct. The analysis was carried out at the two-dimensional level and the turbulent fluxes are represented by a two equation model of turbulence. The existence of such velocity profiles has been accepted previously but the nature of their growth along a pipe was not known previous to this work.

Comparison of Turbulence Models for Single Sphere Simulation Study Under Supercritical Fluid Condition

2017 ◽  
Vol 12 (4) ◽  
Author(s):  
J. Malang ◽  
P. Kumar ◽  
A. Saptoro ◽  
M. O. Tade
Keyword(s):  
Carbon Dioxide ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Near Wake ◽  
Supercritical Conditions ◽  
Flow Features ◽  
Single Sphere ◽  
Simulation Results

AbstractIn this paper, the comparison of turbulence models for fluid flow past single sphere under supercritical conditions is reported. Firstly, Dixon et al.’s models [1], which are under non-supercritical conditions, were used as benchmarks to validate the simulated results. Two turbulence models namely RNGk-εand SSTk-ωmodels parameters were fine-tuned accordingly in order to obtain almost comparable results generated by Dixon et al.’s models [1]. The simulation works were then extended to simulate flow of supercritical carbon dioxide. The second part of this paper, therefore, presents a comparative study of the turbulence models i. e. standardk-ε, RNGk-ε, realizablek-εand SSTk-ωmodels. This study emphasises on the predictions and evaluations of the velocity profiles at different flow regimes namely recirculation, recovery and near-wake. Simulations were carried out to determine the velocity profiles at subcritical and supercritical conditions by varying Reynolds numbers (2000 and 20,000), pressures (65 and 80 bar) and temperatures (283.15 and 308.15K). Simulation results indicate that the predicted results are consistent with the literature data. Interesting flow features were identified for all the simulations. The results of this study also reveal that the SSTk-ωturbulence model was able to better capture the flow characteristics near-wake of the sphere.

Photoinitiated hydrogen-atom reactions in carbon dioxide-hydrogen bromide complexes

1991 ◽  
Vol 95 (21) ◽  
pp. 8048-8053 ◽  
Author(s):  
Seung Koo Shin ◽  
Curt Wittig ◽  
William A. Goddard
Keyword(s):  
Carbon Dioxide ◽  
Hydrogen Atom ◽  
Hydrogen Bromide
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