Abstract

A combined molecular dynamics (MD) and Monte Carlo approach was used to bridge time scales, enabling calculations of surface recombination rates for hydrogen on silica. MD was used for temperatures between 10 and 600 K at a high pressure of 10 atm, yielding recombination coefficients between 0.1 and 1. For the lower pressures more common in applications, low recombination rates make the corresponding calculations intractably expensive. A Monte Carlo technique, informed by the MD simulations, was designed to bridge the essential time scales. Distinct weak and strong surface binding sites for atomic hydrogen with densities of approximately 10 nm-2 were found using grand canonical Monte Carlo (GCMC) simulations, which, in turn, were used to obtain Eley-Rideal rate constants based on semiequilibrium theory. Monte Carlo variational transition state theory (MCVTST) was used to calculate Langmuir-Hinshelwood and thermal desorption rate constants for hydrogen atoms in strong and weak adsorption sites. Calculated reaction rates were used in a Langmuir kinetics model to estimate the recombination coefficient for T = 10-2000 K at gas-phase radical densities between 1012 and 1016 cm-3, yielding values of = 10-4-0.9.

Original languageEnglish (US)
Pages (from-to)24137-24147
Number of pages11
JournalJournal of Physical Chemistry C
Volume120
Issue number42
DOIs
StatePublished - Oct 27 2016

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hydrogen recombinations
Silicon Dioxide
Molecular dynamics
Hydrogen
Silica
silicon dioxide
recombination coefficient
Rate constants
molecular dynamics
Thermal desorption
Binding sites
Reaction rates
hydrogen
Gases
Binding Sites
Adsorption
hydrogen atoms
Atoms
reaction kinetics
Kinetics

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Hydrogen Recombination Rates on Silica from Atomic-Scale Calculations. / Mackay, Kyle K.; Freund, Jonathan B.; Johnson, Harley T.

In: Journal of Physical Chemistry C, Vol. 120, No. 42, 27.10.2016, p. 24137-24147.

Research output: Contribution to journalArticle

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N2 - A combined molecular dynamics (MD) and Monte Carlo approach was used to bridge time scales, enabling calculations of surface recombination rates for hydrogen on silica. MD was used for temperatures between 10 and 600 K at a high pressure of 10 atm, yielding recombination coefficients between 0.1 and 1. For the lower pressures more common in applications, low recombination rates make the corresponding calculations intractably expensive. A Monte Carlo technique, informed by the MD simulations, was designed to bridge the essential time scales. Distinct weak and strong surface binding sites for atomic hydrogen with densities of approximately 10 nm-2 were found using grand canonical Monte Carlo (GCMC) simulations, which, in turn, were used to obtain Eley-Rideal rate constants based on semiequilibrium theory. Monte Carlo variational transition state theory (MCVTST) was used to calculate Langmuir-Hinshelwood and thermal desorption rate constants for hydrogen atoms in strong and weak adsorption sites. Calculated reaction rates were used in a Langmuir kinetics model to estimate the recombination coefficient for T = 10-2000 K at gas-phase radical densities between 1012 and 1016 cm-3, yielding values of = 10-4-0.9.

AB - A combined molecular dynamics (MD) and Monte Carlo approach was used to bridge time scales, enabling calculations of surface recombination rates for hydrogen on silica. MD was used for temperatures between 10 and 600 K at a high pressure of 10 atm, yielding recombination coefficients between 0.1 and 1. For the lower pressures more common in applications, low recombination rates make the corresponding calculations intractably expensive. A Monte Carlo technique, informed by the MD simulations, was designed to bridge the essential time scales. Distinct weak and strong surface binding sites for atomic hydrogen with densities of approximately 10 nm-2 were found using grand canonical Monte Carlo (GCMC) simulations, which, in turn, were used to obtain Eley-Rideal rate constants based on semiequilibrium theory. Monte Carlo variational transition state theory (MCVTST) was used to calculate Langmuir-Hinshelwood and thermal desorption rate constants for hydrogen atoms in strong and weak adsorption sites. Calculated reaction rates were used in a Langmuir kinetics model to estimate the recombination coefficient for T = 10-2000 K at gas-phase radical densities between 1012 and 1016 cm-3, yielding values of = 10-4-0.9.

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