Sticking coefficient and pressure dependence of desorption rate in the statistical rate theory approach to the kinetics of gas adsorption. Carbon monoxide adsorption/desorption rates on the polycrystalline rhodium surface

Abstract

The statistical rate theory (SRT) fundamental kinetic equation for the Langmuir model of adsorption reveals some features which are difficult to understand. These are the infinitely high adsorption rate for zero coverage limit, infinitely high desorption rate at full saturation of the surface and dependence of the desorption rate on the adsorbate pressure. These features do not allow for a correct formulation of such important physical parameters as sticking and initial sticking probabilities. In this work these peculiar features of the fundamental SRT kinetic equation are discussed and explained. It is shown that the non-physical behavior of the SRT kinetic equation follows from neglecting possible changes of adsorbate concentration near the adsorbing surface. A simple model accounting for the changes of adsorbate concentration close to the adsorbing surface is discussed. As a result, it was shown that application of even such a simple model leads to fully physical behavior of the SRT kinetic equation for the Langmuir model of adsorption. The model is used to build up equations describing the kinetics of adsorption/desorption of carbon monoxide on the energetically heterogeneous rhodium surface. The values of the parameters in these equations were determined from the analysis of equilibrium adsorption isotherms and from the description of experimental conditions. One additional parameter (having well defined limiting values) had to be adjusted in order to satisfactorily reproduce kinetic data. The experimental data used in this work were taken from the article by Yamada and Tamaru (T. Yamada and K. Tamaru, Surf. Sci., 1984, 138, L155).

Adsorption and desorption kinetics of benzene derivatives on mesoporous carbons

“…Such initial behavior is similar to the SRT, which is based on Langmuir isotherm, but uses a different kinetic equation Panczyk 2000, 2002a, b;Marczewski 2011) (please note, that re-interpretations of the classic SRT may avoid initial infinite rates, see e.g. Panczyk 2006). It is also the main difference with respect to all the equations derived from the classic kinetic Langmuir equation.…”

“…On the other hand, intraparticle diffusion (IDM) (Crank 1954) and pore diffusion (PDM) (McKay et al 1996) models describe systems where adsorbate diffusion is the main factor responsible for sorption kinetics (Plazinski et al 2009). While such models as LF-mRSK (Marczewski 2011), classic SRT (Rudzinski and Panczyk 2000;Plazinski et al 2009;Podkoscielny and Nieszporek 2011), SRT re-interpretations (Panczyk 2006;Rudzinski and Plazinski 2008) or modifications (Azizian and Bashiri 2008) offer superior level of system description by incorporating various effects, the number of parameters makes them much more susceptible to experimental deviations and may potentially lead to partly supported conclusions. Inappropriate (too narrow) data range may have even more profound effect on data analyses allowing in fact to fit ''reasonable well'' almost any kind of equation.…”

“…IKL was recently extended to include lateral interactions according to regular solution theory and the Kiselev association model as well as energetic heterogeneity (mRSK and LF-mRSK models) (Marczewski 2011). This model was also compared to the classic SRT model, corresponding to the same equilibrium isotherms but developed in opposition to the classic Langmuir kinetics (Ward and Findlay 1982;Zhdanov 2001;Rudzinski and Panczyk 2002a, b;Panczyk 2006;Plazinski et al 2009). Moreover, a new ''fractal-like'' ''approach'' to MOE, IKL and SRT models provided other possible extensions to those equations (Haerifar and Azizian 2012).…”

Degradation Mechanisms in Solid-Oxide Fuel and Electrolyzer Cells: Analytical Description of Nickel Agglomeration in a Ni/YSZ Electrode

“…The adsorption reaction-rate coefficient of species i in Eq. (E1) can be calculated with the help of the Langmuir-Hertz equation [47,48]…”

Oxidation of CO on surface hematite in high CO2 atmospheres

“…There are numerous theoretical studies which are investigating this issue (e.g. Panczyk, 2006;Bulgakov and Sadykov, 1996;Reddy et al, 2004).…”