Benchmark calculations of thermal reaction rates. I. Quantal scattering theory

1991 ◽  
Vol 94 (3) ◽  
pp. 2040-2044 ◽  
Author(s):  
David C. Chatfield ◽  
Donald G. Truhlar ◽  
David W. Schwenke
Keyword(s):  
Scattering Theory ◽  
Reaction Rates ◽  
Thermal Reaction

Photodissolution of iron oxides. IV. A comparative study on the photodissolution of hematite, magnetite, and maghemite in EDTA media

1992 ◽  
Vol 70 (9) ◽  
pp. 2502-2510 ◽  
Author(s):  
Marta I. Litter ◽  
Miguel A. Blesa
Keyword(s):  
Reaction Rates ◽  
Thermal Reaction ◽  
Oxidation Products ◽  
Experimental Conditions ◽  
Spinel Type ◽  
Long Term Stability ◽  
Initiation Step ◽  
Edta Complexes ◽  
Photooxidation Reaction

The thermal and 254-nm photochemical dissolution reactions of magnetite (Fe3O4), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) suspended in EDTA aqueous solutions were compared. γ-Fe2O3 and Fe3O4 are thermally and photochemically more reactive than α-Fe2O3. Both thermal and photochemical dissolution reactions are governed by an initiation step, which involves the production of FeIIaq, and a subsequent thermal reaction of these ions with the solid, to produce FeIIIaq. The initiation step under UV irradiation involves the photoreduction of surface >FeIII – EDTA complexes to yield FeIIaq and the photooxidation of adsorbed EDTA to yield CH2O and other oxidation products. After FeIII – EDTA complexes build up in solution through the following step, homogeneous photolysis is the main source of FeII and CH2O. Oxides with spinel type structure are characterized by faster rates in the two processes, and O2 may inhibit the dissolution processes by changing the stoichiometry of the initiation step to that of the autooxidation of EDTA. The relative importance of autooxidation and photodissolution depends on the nature of the oxide and the experimental conditions. Photooxidation reaction rates parallel those of the photodissolution initiation steps, and long-term stability towards photocorrosion (dissolution) implies low photocatalytic activity for the oxidation of EDTA. The set of differential equations describing all the reaction rates is discussed and applied to the different cases.

Photoenhancement of Gas-Solid Reactions by Surface Excitation

1983 ◽  
Vol 29 ◽  
Author(s):  
Carol I. H. Ashby
Keyword(s):  
Thermal Effects ◽  
Kinetic Studies ◽  
Wavelength Dependence ◽  
Reaction Rates ◽  
Thermal Reaction ◽  
Subsequent Formation ◽  
Rate Limiting Step ◽  
Surface Excitation ◽  
Rate Limiting ◽  
Reactive Excited State

ABSTRACTUltraviolet irradiation of the surface of graphite leads to the enhancement of the reaction of graphite with hydrogen to form methane under conditions where photo-induced thermal effects are negligible. Wavelength dependence of the photoenhancement correlates with excitation of the π-valence to π-conduction transition of graphite centered at 260 nm. Subsequent formation of some reactive excited state species leads to enhanced reaction rates. Likely candidates for such reactive species have been identified by comparative kinetic studies of the thermal and the photoenhanced reactions. For example, at low temperatures (< 500 K), the rate-limiting step of the thermal reaction is addition of H to surface CH3 groups, and the observed photoenhancement can be explained by activation of these CH3 groups.

scholarly journals Plasma-Catalytic Ammonia Synthesis Beyond the Equilibrium Limit

2020 ◽  
Author(s):  
Prateek Mehta ◽  
Patrick M. Barboun ◽  
Yannick Engelmann ◽  
David B. Go ◽  
Annemie Bogaerts ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Ammonia Synthesis ◽  
Packed Bed ◽  
Reaction Rates ◽  
Thermal Reaction ◽  
Equilibrium Limit ◽  
Plasma Activation ◽  
Catalytic Material ◽  
Material Choice ◽  
Catalytic Ammonia Synthesis

We explore the consequences of non-thermal plasma activation on product yields in catalytic ammonia synthesis, a reaction that is equilibrium-limited at elevated temperatures. We employ a minimal microkinetic model that incorporates the influence of plasma activation on N<sub>2</sub> dissociation rates to predict NH<sub>3</sub> yields into and across the equilibrium-limited regime. NH<sub>3</sub> yields are predicted to exceed bulk thermodynamic equilibrium limits on materials that are thermal-rate-limited by N<sub>2</sub> dissociation. In all cases, yields revert to bulk equilibrium at temperatures at which thermal reaction rates exceed plasma-activated ones. Beyond-equilibrium NH<sub>3</sub> yields are observed in a packed bed dielectric-barrier-discharge reactor and exhibit sensitivity to catalytic material choice in a way consistent with model predictions. The approach and results highlight the opportunity to exploit synergies between non-thermal plasmas and catalysts to affect transformations at conditions inaccessible through thermal routes.

scholarly journals Plasma-Catalytic Ammonia Synthesis Beyond the Equilibrium Limit

2020 ◽  
Author(s):  
Prateek Mehta ◽  
Patrick M. Barboun ◽  
Yannick Engelmann ◽  
David B. Go ◽  
Annemie Bogaerts ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Ammonia Synthesis ◽  
Packed Bed ◽  
Reaction Rates ◽  
Thermal Reaction ◽  
Equilibrium Limit ◽  
Plasma Activation ◽  
Catalytic Material ◽  
Material Choice ◽  
Catalytic Ammonia Synthesis

We explore the consequences of non-thermal plasma activation on product yields in catalytic ammonia synthesis, a reaction that is equilibrium-limited at elevated temperatures. We employ a minimal microkinetic model that incorporates the influence of plasma activation on N<sub>2</sub> dissociation rates to predict NH<sub>3</sub> yields into and across the equilibrium-limited regime. NH<sub>3</sub> yields are predicted to exceed bulk thermodynamic equilibrium limits on materials that are thermal-rate-limited by N<sub>2</sub> dissociation. In all cases, yields revert to bulk equilibrium at temperatures at which thermal reaction rates exceed plasma-activated ones. Beyond-equilibrium NH<sub>3</sub> yields are observed in a packed bed dielectric-barrier-discharge reactor and exhibit sensitivity to catalytic material choice in a way consistent with model predictions. The approach and results highlight the opportunity to exploit synergies between non-thermal plasmas and catalysts to affect transformations at conditions inaccessible through thermal routes.

scholarly journals SOFT PHOTON PRODUCTION FROM QUARK–GLUON PLASMA AND CANCELLATION OF MASS SINGULARITY

1995 ◽  
Vol 10 (05) ◽  
pp. 379-389 ◽  
Author(s):  
A. NIÉGAWA
Keyword(s):  
Production Rate ◽  
Quark Gluon Plasma ◽  
General Theorem ◽  
Reaction Rates ◽  
Gluon Plasma ◽  
Thermal Reaction ◽  
Final States ◽  
Physical Processes ◽  
The One ◽  
Vacuum Theory

It has recently been reported that the production rate of soft real photons from a hot quark–gluon plasma exhibits unscreened mass singularities even within the hard-thermal-loop resummation scheme. It is shown that there exist another diagrams that cancel the singular contribution, in accordance with the general theorem of absence of mass singularities in thermal reaction rates, provided one sums over the set of all degenerate initial and final states. An interpretation of the relevant diagrams is given in terms of physical processes taking place in the quark–gluon plasma. The mechanism of canceling mass singularities in this example is similar to the one in vacuum theory.

Thermal reaction rates with a two-point flux-flux correlation function

1994 ◽  
Vol 51 (6) ◽  
pp. 465-472 ◽  
Author(s):  
R. Lefebvre ◽  
N. Moiseyev ◽  
V. Ryaboy
Keyword(s):  
Correlation Function ◽  
Reaction Rates ◽  
Thermal Reaction
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