Statistical rate theory of interfacial transport. IV. Predicted rate of dissociative adsorption

Ward

1997

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Absolute rate theory and the sticking probability approach have been previously examined as possible means of predicting the rate of adsorption. However, when applied to examine adsorption kinetics, they have been found not to contain the coverage and pressure dependence required for several important systems including CO–Ni(111). Statistical rate theory (SRT) is being developed with the objective of predicting the rate of molecular (or atomic) transport across the interface between macroscopic phases in terms of experimentally controllable variables and material properties of the two phases. Previous applications of SRT to adsorption have been limited to systems for which both the gas phase pressure and the temperature could be assumed to be constant. Herein, the SRT approach is extended to systems in which the number of molecules in the system (and hence the gas phase pressure) is not constant. To examine this extension, SRT is used to formulate the equations governing the rate of adsorption in isothermal, beam-dosing experiments. These equations are then combined with the values of certain material properties that have previously been established and a hypothesis that the value of the equilibrium adsorption cross section is given by the area of an adsorption site. The kinetic data for CO adsorbing on Ni(111) data reported by three different laboratories are then examined. For each set of experimental data, constants had to be inferred that were related to the experimental apparatus used and as such they were not expected to have any coverage or pressure dependence. The good agreement found between the predicted and measured adsorption kinetics indicates that all of the necessary coverage and pressure dependence was explicitly predicted from the SRT approach.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Statistical rate theory description of beam-dosing adsorption kinetics

Ward

1997

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“…39,40,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] Statistical rate theory was first proposed by C. A. Ward in an elementary form in 1977, 45 and is based on the quantum-mechanical transition probability in an isolated, many particle system.…”

Section: Introductionmentioning

confidence: 99%

“…Electronic mail: janet.elliott@ualberta.ca dynamic equilibrium. Since its inception, statistical rate theory has been applied to a variety of rate processes including: electron exchange between isotopes in solution, 40,46 gas-solid adsorption, 40,44,[52][53][54][55] gas absorption at a liquid interface, [47][48][49] hydrogen absorption by metals, 50 permeation in ionic channels in biological membranes, 51 crystal growth from solution, 56 and evaporation. 57,58 In each case, the statistical rate theory approach led to improvement in the theoretical description of the rate process.…”

Section: Introductionmentioning

confidence: 99%

A statistical rate theory description of CO diffusion on a stepped Pt(111) surface

Torri

1999

The statistical rate theory approach is used to describe far-from-equilibrium diffusion of carbon monoxide on a stepped Pt͑111͒ surface at low total coverages. Under nonequilibrium conditions, migration of adsorbates from terraces to steps, where adsorbates are more strongly bound, can occur. An expression for the molecular transport rate between terraces and steps is derived in terms of an equilibrium exchange rate, and the instantaneous chemical potentials of the molecules adsorbed on the terraces and along the steps. The theory contains no free parameters. Both the equilibrium exchange rate and the chemical potentials are obtained in the framework of a lattice gas model. The time evolution of the populations of steps and terraces is calculated and used to fit the available experimental data in order to evaluate the activation barrier of diffusion on terraces and the associated prefactor.

“…Statistical rate theory ͑SRT͒ shows promise of overcoming this difficulty since it has been shown to predict the coverage dependence of isothermal adsorption kinetics. [6][7][8][9][10] Statistical rate theory was originally developed to allow the rate of molecular transport across the interface between macroscopic phases of an isolated system to be predicted in terms of the material properties of the two phases. [6][7][8][9][11][12][13][14][15][16][17][18] Recently, this approach was extended so that it could be applied to a nonisolated system that experienced a change in mass during the kinetic process.…”

Section: Introductionmentioning

confidence: 99%

Temperature programmed desorption: A statistical rate theory approach

Ward

1997

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Articles you may be interested inDesign and construction of a semiautomatic temperature programmed desorption apparatus for ultrahigh vacuum J. Vac. Sci. Technol. A 23, 215 (2005); 10.1116/1.1818133Microsystem with integrated capillary leak to mass spectrometer for high sensitivity temperature programmed desorption Rev. Sci. Instrum. 75, 3345 (2004); 10.1063/1.1791851 Quantification of lateral repulsion between coadsorbed CO and N on Rh(100) using temperature-programmed desorption, low-energy electron diffraction, and Monte Carlo simulations Development of a temperature-programed electron-stimulated desorption ion angular distribution/time-of-flight system for real-time observation of surface processes and its application to adsorbed layers on Ru(001) Rev. Sci. Instrum. 69, 3666 (1998); 10.1063/1.1149156Temperature-programmed desorption study of the etching of Ni(110) with 2,4-pentanedione J.The equation traditionally used to interpret temperature programmed desorption ͑TPD͒ spectra, the Polanyi-Wigner equation, does not contain explicitly the coverage and temperature dependence necessary to predict TPD spectra in several important systems including CO-Ni͑111͒. Herein, the statistical rate theory ͑SRT͒ approach is used to formulate equations for temperature programmed desorption which are then used to examine TPD spectra reported in the literature for CO-Ni͑111͒. The molecular and material properties for the CO-Ni͑111͒ system have been previously established. One experimental spectrum has been chosen to determine the apparatus constants. The material properties and the apparatus constants are then used in the SRT equations to predict the eight additional TPD spectra for different initial coverages. A critical comparison can then be made between the theory and these eight experimental spectra, since no fitting constants were used in these eight cases. The results show that there is clearly qualitative agreement. The SRT equations are then used along with the heat of adsorption to derive an equation for the pre-exponential factor appearing in the Polanyi-Wigner equation. A prediction is made for the pre-exponential factor that is in agreement with that found empirically. The agreement found between the SRT predictions and the measured spectra indicates that all of the coverage and temperature dependence necessary to predict TPD spectra is given explicitly by the SRT approach. Hence, the experimental support for the SRT approach is enhanced. The SRT equations are then used to predict CO-Ni͑111͒ spectra that would occur if the heating rate were varied.