Chemical reactions on solid surfaces

Zaera, F. (2002) Infrared and molecular beam studies of chemical reactions on solid surfaces , Int. Rev. Phys. Chem., 21, 433. 

Chemical reactions on solid surfaces can be realized in gas-solid and liquid-solid systems. In both cases the reaction takes place on the surface of the solid matrix, and therefore the molecules to be reacted need to get in contact with the reactive surface. Several transport regimes and interaction mechanisms define the mass transfer efficiency. They can be summarized as follows [6] ... 

F. Zaera, Kinetics of chemical reactions on solid surfaces. Deviations from conventional theory, Accounts of Chemistry Research, 35 (2002) 129. 

Zhdanov, V. and Zamaraev, K. (1982). Vibrational relaxation of adsorbed molecules. Mechanism and manifestation in chemical reactions on solid surface. Catal. Rev. Sci. Eng., 24 373-413. 

The simplest solid-state membranes are designed to measure test ions, which are also the mobile ions of the crystal (first-order response) and are usually single-substance crystals (Figure 4.11). Alternatively, the test substance may be involved in one or two chemical reactions on the surface of the electrode which alter the activity of the mobile ion in the membrane (Figures 4.12 and 4.13). Such membranes, which are often mixtures of substances, are said to show second- and third-order responses. While only a limited number of ions can gain access to a particular membrane, a greater number of substances will be able to react at the surface of the membrane. As a result, the selectivity of electrodes showing second- and third-order responses is reduced. 

Chemical kinetics deductions are, in some circumstances, possible from a reaction system using a dispersed solid. If the solid is entirely insoluble, for example a supported catalyst, true surface kinetics can be obtained provided (i) it can be shown that the chemical reaction on the surface is much slower than the associated mass transfer, and (ii) the surface area of the solid can be obtained. These conditions applied in the case of the oxidation of an aqueous solution of hydrazine using a dispersion of insoluble barium chromate [16]. Another case is where it can be shown that an increase in the amount of the solid component does not increase the reaction rate. In this case, exemplified by the formation of benzyl acetate from benzyl bromide and solid sodium acetate in toluene solvent, it is likely that the reaction occurs in the solution phase and that the reaction is proceeding at the saturation concentration of the solid reactant in the liquid phase [17]. 

Previous books in this area typically focus on selected aspects of the subject, such as the properties of the solid phase, or the interactions of selected substances with soil/rock. This book comprehensively treats the soil-liquid-interface system. Drawn chiefly from the authors years of research at the Isotope Laboratory in the Department of Colloid and Environmental Chemistry at the University of Debrecen in Hungary, this book discusses chemical reactions on the surfaces/interfaces of soils and rocks examines the role of these processes in environmental, colloid and geochemistry and explores the effects on agricultural, environmental and industrial applications. 

Masel R.I. Principles of adsorption and reaction on solid surfaces, Wiley Series in Chemical Engineering ( John Wiley Sons New York 1996) 769-776. 

V. P. Zhdanov and B. Kasemo, Bistable kinetics of simple reactions on solid surfaces lateral interactions, chemical waves, and the equistabil-ity criterion, Physica D, 70 (1994) 383. 

One important aspect of heterogeneous chemical reactions at solid surfaces is related to the presence of adsorbed species that play a key role in determining the rate and efficiency of these processes. Therefore, the knowledge of molecular arrangements on solid catalysts of reactants, reaction intermediates, or products is of outstanding importance in dealing with fundamental aspects of heterogeneous catalysis. 

Problem 9.5 Considering reaction between A and B catalyzed by a solid there are two possible mechanisms by which this reaction could occur. The first is that one of them, say A gets adsorbed on the solid surface and the adsorbed A then reacts chemically with the other component B which is in the gas phase or in solution and is not adsorbed on the surface. The second mechanism is that both A and B are adsorbed, and the adsorbed species undergo chemical reaction on the surface. The reaction rate expression derived for the former mechanism is the Rideal rate law and that for the second mechanism is the Langmuir-Hinshelwood rate law. Obtain simple derivations of these two rate laws. 

Reactions taking place on the surface of solid or liquid particles and inside liquid droplets play an important role in the middle atmosphere, especially in the lower stratosphere where sulfate aerosol particles and polar stratospheric clouds (PSCs) are observed. The nature, properties and chemical composition of these particles are described in Chapters 5 and 6. Several parameters are commonly used to describe the uptake of gas-phase molecules into these particles (1) the sticking coefficient s which is the fraction of collisions of a gaseous molecule with a solid or liquid particle that results in the uptake of this molecule on the surface of the particle (2) the accommodation coefficient a which is the fraction of collisions that leads to incorporation into the bulk condensed phase, and (3) the reaction probability 7 (also called the reactive uptake coefficient) which is the fraction of collisions that results in reactive loss of the molecule (chemical reaction). Thus, the accommodation coefficient a represents the probability of reversible physical uptake of a gaseous species colliding with a surface, while the reaction probability 7 accounts for reactive (irreversible) uptake of trace gas species on condensed surfaces. This latter coefficient represents the transfer of a gas into the condensed phase and takes into account processes such as liquid phase solubility, interfacial transport or aqueous phase diffusion, chemical reaction on the surface or inside the condensed phase, etc. 

The first kinetic approach in catalysis based on a physical chemical understanding is due to I. Langmuir, the Nobel Prize in Chemistry winner in 1932, who applied the mass action law to reaction on solid surfaces, e.g the rate of an elementary reaction was supposed to be proportional to the surface concentration (coverage) of reactive species adsorbed on the surface. 

S. A. Adelman and J. D. Doll, Brownian motion and chemical dynamics on solid surfaces, Acc. Chem. Res. 10 378 (1977) S. A. Adelman, Chemical reaction dynamics in liquid solution, Adv. Chem. Phys. 53 61 (1983). 

Adsorption is a necessary step preceding the actual chemical reaction on solid catalyst surfaces. 

The controlling resistance can be one of the following (1) diffusion through the kerosene film surrounding the solid, (2) diffusion through an increasing layer of solid product (known as ash in gas-solid literature, but it is not an appropriate term for the solid product of a solid-liquid reaction) (3) chemical reaction on the surface of the receding reactant core or (4) combinations of the three. 

Under otherwise equal conditions, the covalently rigidly bound particles in a solid should expend more energy in overcoming bond forces on passii into solution, and their dissolution should be accompanied by higher activation energies, than in the dissolution of ionic solids. It is known that the rate of dissolution of solids containing a covalent bond is determined by the rate of chemical reaction on the surface of these substances with an activation energy s 10 kcal/mole. 

Masel, R. I. 1996. Principles of Adsorption and Reaction on Solid Surfaces, WUey Series in Chemical Engineering. WUey-Interscience New York, 1996. 

Catalytic reaction mechanisms represent the elementary steps at molecular level, but the expression in detail at molecular level is difficult for the catalytic reactions on solid surfaces. So, the usual strategy is to propose applicable reaction mechanisms for key chemical processes occurring on catalyst surface, based on a series of assumptions that must be in agreement with experimental data and could be modified indispensably. 

In case of the interaction of a solid with active medium, it may lead both to plasticity increase and to its reduction (accompanied by hardening), depending on the results of surface chemical (electrochemical) reactions. E. M. Gutman has discovered in 1967 that (electro)chemical reactions on the surface of a stressed solid cause additional dislocation flux, which changes... 

Thus, the use of the XPS method gives us a clear idea of chemical reactions on the surface of a solid body, which helps optimise manufacturing techniques of objects with desired properties. 

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