Enthalpies and Entropies of Adsorption on Well-Defined Oxide Surfaces: Experimental Measurements

Campbell, Charles T.; Sellers, Jason R. V.

doi:10.1021/cr300329s

Cited by 230 publications

(293 citation statements)

References 261 publications

Supporting

Mentioning

278

Contrasting

Order By: Relevance

“…The next step is to estimate values of binding energies for adsorption of all species on the surface, for example using experimental results from the literature, results from DFT calculations, or scaling relations (20)(21)(22)(23)(24). In addition, it is necessary to estimate values for the entropies of the adsorbed species, for example using results from experimental studies (25), correlations in the literature (26), results from DFT calculations of vibrational frequencies (27)(28)(29)(30)(31)(32)(33)(34), combined with hindered translator and hindered rotor models for the three modes associated with motion parallel to the surface (35,36), or by assuming models for the extent of mobility on the surface. It is now possible to estimate values for lumped equilibrium constants, K ads,i , to form the adsorbed species from the reactants and/or products, followed by calculation of θ p .…”

Section: Analytical Strategy For Analysis Of Reaction Schemesmentioning

confidence: 99%

Analysis of reaction schemes using maximum rates of constituent steps

Motagamwala

Dumesic

2016

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, r max,i , assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of r max,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of r max,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps.chemical kinetics | catalysis | microkinetics C hemical reactions take place through sequences of elementary steps, and the dynamics of the overall stoichiometric reaction are typically controlled by key steps in this sequence of steps. For example, in the case of a catalytic reaction, the reaction kinetics are controlled by the energetics of the transition states for the rate-controlling steps and by the energetics of species that are abundant on the active sites (i.e., the Gibbs free energies of these transition states and adsorbed species relative to the reactants and products of the overall stoichiometric reaction). However, whereas the observed reaction kinetics are controlled by a limited number of transition states and adsorbed species, it is typically required to carry out detailed microkinetic analyses to identify the nature of these key transition states and adsorbed species. Thus, a general strategy to elucidate how the reaction kinetics are controlled by a proposed reaction mechanism is first to carry out density functional theory (DFT) calculations to determine the thermodynamic properties of all adsorbed species and transition states, and then to build a microkinetic model to determine the surface coverages by all adsorbed species and the forward and reverse rates of all elementary steps for a range of reaction conditions (1-5). Sensitivity analyses are then carried out using this microkineti...

show abstract

Section: Analytical Strategy For Analysis Of Reaction Schemesmentioning

confidence: 99%

Analysis of reaction schemes using maximum rates of constituent steps

Motagamwala

Dumesic

2016

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…36 The experimentally measured enthalpies and entropies of adsorption of relatively small molecules on oxide surfaces have been summarized in ref. 37 However, detailed studies of the adsorption of large organic molecules at insulating surfaces are still challenging and often confined to static simulations.…”

Section: 32mentioning

confidence: 99%

Calculating the Entropy Loss on Adsorption of Organic Molecules at Insulating Surfaces

et al. 2016

View full text Add to dashboard Cite

Although it is recognized that dynamic behavior of adsorbing molecules strongly affects the entropic contribution to adsorption free energy, detailed studies of the adsorption entropy of large organic molecules at insulating surfaces are still rare. We compared adsorption of two different functionalized organic molecules, 1,3,5-tri-(4-cyano-4,4 biphenyl)-benzene (TCB) and 1,4-bis(cyanophenyl)-2,5-bis(decyloxy)benzene (CDB), on the KCl (001) surface using density functional theory (DFT) and molecular dynamics (MD) simulations. The accuracy of the van der Waals corrected DFT-D3 was benchmarked using Møller-Plesset perturbation theory calculations. Classical force fields were then parameterized for both the TCB and CDB molecules on the KCl (001) surface. These force fields were used to perform potential of mean force (PMF) calculations of adsorption of individual molecules and extract information on the entropic contributions to adsorption energy. The results demonstrate that entropy losses upon adsorption are significant for flexible molecules, such as considered here, and even at relatively low temperatures (e.g. 400 K) can match the enthalpy contribution to adsorption energy.

show abstract

“…A wide variety of equilibrium isotherm models (Langmuir, Freundlich, Brunauer-Emmett-Teller, Redlich-Peterson, DubininRadushkevich (D-R), Temkin, Toth, Koble-Corrigan, Sips, Khan, Hill, Flory-Huggins and Radke-Prausnitz isotherm), have been formulated till date to describe the experimental sorption data [20,21]. Among the existing theoretical adsorption models, Langmuir is the simplest one to describe the adsorption on homogeneous surface.…”

Section: Mathematical Models Of Adsorption Isothermsmentioning

confidence: 99%