Simultaneous adsorption and reaction

Z stands for the zeolite framework. In the direct pathway (Eq. (28)), two methanol molecules react with each other on one Bronsted acid site 282). This pathway involves the simultaneous adsorption and reaction of two methanol molecules, with the formation of one DME and one water molecule in a single step ... 

Two novel hybrid concepts for gas separation using adsorption technology have emerged in recent years. They include (a) adsorbent membranes, and (b) simultaneous adsorption and reaction. 

Gas exchange during catalytic reaction between bubbles and the emulsion of catalyst particles is essentially a diffusional phenomenon, with simultaneous adsorption and reaction in the emulsion. Based on this concept, the overall mass transfer has been analyzed by Miyauchi and... 

Less generally applicable than electron or scanning probe microscopy, but capable of revealing great detail, are field emission and field ion microscopy (FEM and F1M). These techniques are limited to the investigation of sharp metallic tips, however, with the attractive feature that the facets of such tips exhibit a variety of crystallographically different surface orientations, which can be studied simultaneously, for example in gas adsorption and reaction studies. 

Chromatographic fixed-bed reactors consists of a single chromatographic column containing a solid phase on which adsorption and reaction take place. Normally a pulse of reactant is injected into the reactor and, while traveling through the reactor, simultaneous conversion and separation take place (Fig. 3). Since an extensive overview of the models and applications of this type of reactor was presented by Sardin et al. [ 132], only a few recent results will be discussed here. Most of the practical applications have been based on gas-liquid systems, which are not applicable for the enzyme reactions, but a few reactions were also reported in the liquid phase. One of these studies, performed by Mazzotti and co-workers [ 141 ], analyzed the esterification of acetic acid into ethyl acetate according to the reaction ... 

Since the reaction kinetics is of the Langmuir-Hinshelwood type additional informations about the adsorption of reactants is helpful in the development of a kinetic model. Therefore experiments have been carried out by use of an experimental setup for adsorption measurements. Since adsorption and reaction occur simultaneously the change of gas composition in the adsorption cell is registrated by on-line GC-MS. Then the amount of adsorbed substances is calculated as the difference of added substance and substance in the gas phase of the adsorption cell given by the total pressure in the cell and the gas composition. A schematic drawing of the... 

The role of adsorption in heterogeneous catalysis is not easily evaluated because of the simultaneous occurrence of adsorption and reaction and the difficulty of measuring surface concentrations of reacting species on the catalyst at these conditions. Exploratory research directed toward devising a method for studying adsorption in gas-solid systems by means of a batch adsorber-reactor has been underway in this laboratory for several years. 

Variation of the trlalkylaluminium concentration can bring about considerable changes in the rate-time profiles for hgCl - supported catalysts. The changes observed are quite complex and are believed to arise from simultaneous adsorption and reduction reactions (11). 

Adsorption of single surfactants or nitrophenol is already a complex process involving several physico-chemical factors. The phenomena become even more complicated when different types of molecules compete for adsorption at the interface. With respect to competitive adsorption, distinction has to be made between simultaneous adsorption and displacement reactions. SERS spectroscopy is probably one of tbe most sensitive and chemically specific methods for investigating the processes at the solid/liquid interface because the signals of the coadsorbed CPC and PNP molecules can be observed simultaneously in the first monolayer. 

Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1—18 for cases where the stmcture and properties of a soHd phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Drying simulation (45—47) and drying of foods (48,49) have been particularly active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). Eor these kinds of appHcations psychrometric charts for systems other than air—water would be useful. The constmction of such has been considered (54). 

The effects of adsorbed inhibitors on the individual electrode reactions of corrosion may be determined from the effects on the anodic and cathodic polarisation curves of the corroding metaP . A displacement of the polarisation curve without a change in the Tafel slope in the presence of the inhibitor indicates that the adsorbed inhibitor acts by blocking active sites so that reaction cannot occur, rather than by affecting the mechanism of the reaction. An increase in the Tafel slope of the polarisation curve due to the inhibitor indicates that the inhibitor acts by affecting the mechanism of the reaction. However, the determination of the Tafel slope will often require the metal to be polarised under conditions of current density and potential which are far removed from those of normal corrosion. This may result in differences in the adsorption and mechanistic effects of inhibitors at polarised metals compared to naturally corroding metals . Thus the interpretation of the effects of inhibitors at the corrosion potential from applied current-potential polarisation curves, as usually measured, may not be conclusive. This difficulty can be overcome in part by the use of rapid polarisation methods . A better procedure is the determination of true polarisation curves near the corrosion potential by simultaneous measurements of applied current, corrosion rate (equivalent to the true anodic current) and potential. However, this method is rather laborious and has been little used. 

A number of metals have the ability to absorb hydrogen, which may be taken into solid solution or form a metallic hydride, and this absorption can provide an alternative reaction path to the desorption of H,. as gas. In the case of iron and iron alloys, both hydrogen adsorption and absorption occur simultaneously, and the latter thus gives rise to another equilibrium involving the transfer of H,<,s across the interface to form interstitial H atoms just beneath the surface ... 

The simplest case to be analyzed is the process in which the rate of one of the adsorption or desorption steps is so slow that it becomes itself rate determining in overall transformation. The composition of the reaction mixture in the course of the reaction is then not determined by kinetic, but by thermodynamic factors, i.e. by equilibria of the fast steps, surface chemical reactions, and the other adsorption and desorption processes. Concentration dependencies of several types of consecutive and parallel (branched) catalytic reactions 52, 53) were calculated, corresponding to schemes (Ila) and (lib), assuming that they are controlled by the rate of adsorption of either of the reactants A and X, desorption of any of the products B, C, and Y, or by simultaneous desorption of compounds B and C. 

It is unlikely in real tribological events that adsorbed mono-layers work solely to provide lubrication. Instead, adsorption and chemical reactions may occur simultaneously in most cases of boundary lubrication. For example, fatty acid is usually regarded as a friction modiher due to good adsorp-tivity, meanwhile its molecules can react with metal or a metal oxide surface to form metallic soap which provides protection to the surface at the temperature that is higher than its own melting point. 

Anodic dissolution reactions of metals typically have rates that depend strongly on solution composition, particularly on the anion type and concentration (Kolotyrkin, 1959). The rates increase upon addition of surface-active anions. It follows that the first step in anodic metal dissolution reactions is that of adsorption of an anion and chemical bond formation with a metal atom. This bonding facilitates subsequent steps in which the metal atom (ion) is tom from the lattice and solvated. The adsorption step may be associated with simultaneous surface migration of the dissolving atom to a more favorable position (e.g., from position 3 to position 1 in Fig. 14.1 la), where the formation of adsorption and solvation bonds is facilitated. 

For a surface reaction between two adsorbed gaseous species, A and B, we need to consider the simultaneous adsorption of the two species, competing for the available... 

Soled catalyzed roocUono. These involve simultaneous diffusion, adsorption and surface reaction. See Chapter <5. 

Diffusion of A to the surface and surface reaction between adsorbed A and B occur simultaneously. Adsorption of A is relatively small but a component C also is adsorbed. 

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