Dissociative chemisorption reaction dynamics

We have intentionally left off this wide variety of topics in order to focus on the detailed coverage of the dynamics and interactions of dissociative chemisorption reactions. Our goals are to introduce the concepts in this area, to illustrate these with representative experimental measurements, to present the state-of-the-art theoretical methodology, and to indicate the understanding provided by applications of these theoretical methods. We will try... 

Kroes G J, Wiesenekker G, Baerends E J, Mowrey R C and Neuhauser D 1996 Dissociative chemisorption of H2 on Cu(IOO)—a four-dimensional study of the effect of parallel translational motion on the reaction dynamics J. Chem. Phys. 105 5979... 

The quantum mechanism of dissociative chemisorption of hydrogen and hydrogen-containing molecules is widely discussed in the dynamics of catalytic reactions (see, for instance, Harris and Anderson [1985] and Chiang and Jackson [1987]). 

Theoretically, Wu and Carter146 showed that the 1.5 ML coverage may be explained by the difluoride species. Molecular dynamics simulations by Carter and Carter147 suggested a stepwise mechanism which yields two pathways involving Si—F bond formation (a) F atom abstraction, where one Si—F bond is formed at the expense of the F—F bond while the remaining F atom is ejected from the surface, and (b) dissociative chemisorption, where both F atoms in the incident F2 molecule form Si—F bonds in a consecutive fashion. They showed that, depending on the conditions, the preferred reaction channel varies. 

Without a doubt, a complete picture of the dynamics of dissociative chemisorption and the relevant parameters which govern these mechanisms would be incredibly useful in studying and improving industrially relevant catalysis and surface reaction processes. For example, the dissociation of methane on a supported metal catalyst surface is the rate limiting step in the steam reforming of natural gas, an initial step in the production of many different industrial chemicals [1]. Precursor-mediated dissociation has been shown to play a dominant role in epitaxial silicon growth from disilane, a process employed to produce transistors and various microelectronic devices [2]. An examination of the Boltzmann distribution of kinetic energies for a gas at typical industrial catalytic reactor conditions (T 1000 K)... 

Some aspects related to catalysts characteristic and behaviour will be treated such as determination of metal surface area and dispersion, spillover effect and synterisation. A detailed description of the available techniques will follow, taking in consideration some aspects of the gas-solid interactions mechanisms (associative/dissociative adsorption, acid-base interactions, etc.). Every technique will be treated starting from a general description of the related sample pretreatment, due to the fundamental importance of this step prior to catalysts characterisation. The analytical theories will be described in relation to static and dynamic chemisorption, thermal programmed desorption and reduction/oxidation reactions. Part of the paper will be dedicated to the presentation of the experimental aspects of chemisorption, desorption and surface reaction techniques, and the relevant calculation models to evaluate metal surface area and dispersion, energy distribution of active sites, activation energy and heat of adsorption. 

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