Benchmark calculations of thermal reaction rates. II. Direct calculation of the flux autocorrelation function for a canonical ensemble

1991 ◽  
Vol 94 (3) ◽  
pp. 2045-2056 ◽  
Author(s):  
Paul N. Day ◽  
Donald G. Truhlar
Keyword(s):  
Autocorrelation Function ◽  
Canonical Ensemble ◽  
Direct Calculation ◽  
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.

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

scholarly journals PHASE TRANSITION AND FRAGMENT PRODUCTION IN THE LATTICE GAS MODEL

1999 ◽  
Vol 08 (06) ◽  
pp. 527-544 ◽  
Author(s):  
FRANCESCA GULMINELLI ◽  
PHILIPPE CHOMAZ
Keyword(s):  
Phase Transition ◽  
Gas Phase ◽  
Lattice Gas ◽  
Canonical Ensemble ◽  
Finite Size ◽  
Direct Calculation ◽  
Lattice Gas Model ◽  
Finite Size Scaling ◽  
Finite Size Effects ◽  
Fragment Production

The critical behavior of fragment production is studied within a Lattice Gas Model in the canonical ensemble. Finite size effects on the liquid-gas phase transition are analyzed by a direct calculation of the partition function, and it is shown that phase coexistence and phase transition are relevant concepts even for systems of a few tens of particles. Critical exponents are extracted from the behavior of the fragment production yield as a function of temperature by means of a finite size scaling. The result is that in a finite system well defined critical signals can be found at supercritical (Kertész line) as well as subcritical densities inside the coexistence zone.

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.

Unified Rate Theory of Electrochemistry and Electrocatalysis: Fixed Potential Formulation for General, Electron Transfer, and Proton-Coupled Electron Transfer Reactions

2019 ◽  
Author(s):  
Marko Melander
Keyword(s):  
Electron Transfer ◽  
Electrode Potential ◽  
Canonical Ensemble ◽  
Reaction Rates ◽  
Transfer Reactions ◽  
Rate Theory ◽  
Electron Transfer Reactions ◽  
Proton Coupled Electron Transfer ◽  
Fixed Electrode ◽  
Grand Canonical

<div>Atomistic modeling of electrocatalytic reactions is most naturally conducted within the grand canonical ensemble (GCE) which enables fixed chemical potential calculations. While GCE has been widely adopted for modeling electrochemical and electrocatalytic thermodynamics, the electrochemical reaction rate theory within GCE is lacking. Molecular and condensed phase rate theories are formulated within microcanonical and canonical ensembles, respectively, but electrocatalytic systems described within the GCE require extension of the conventionally used rate theories for computation reaction rates at fixed electrode potentials. In this work, rate theories from (micro)canonical ensemble are generalized to the GCE providing the theoretical basis for the computation reaction rates in electrochemical and electrocatalytic systems. It is shown that all canonical rate theories can be extended to the GCE. From the generalized grand canonical rate theory developed herein, fixed electrode potential rate equations are derived for i) general reactions within the GCE transition state theory (GCE-TST), ii) adiabatic curve-crossing rate theory within the empirical valence bond theory (GCE-EVB), and iii) (non-)adiabatic electron and proton-coupled electron transfer reactions. The rate expressions can be readily combined with ab initio methods to study reaction kinetics reactions at complex electrochemical interfaces as a function of the electrode potential. The theoretical work herein provides a single, unified approach for electrochemical and electrocatalytic kinetics and the inclusion of non-adiabatic and tunneling effects in electrochemical environments widening the scope of reactions amenable to computational studies.</div>

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