Adsorption of products

The liquid phase Friedel-Crafts acylation of thioanisole with iso-butyric anhydride to produce 4-methyl thiobutyrophenone has been studied using supported silicotungstic acid catalysts. Reaction is rapid, giving the para-acylation product in high yield. Reactions have been performed in both batch slurry and trickle bed reactors. In both reactors catalyst deactivation due to strong adsorption of product was observed. 

Another important factor which can significantly affect the shape and position of the voltammetric wave, and hence rate constants, is adsorption of product or reactant on the electrode surface. For a linear adsorption isotherm, if the reactant is adsorbed, a reduction wave will be shifted towards more negative potentials and if the product is adsorbed, towards more positive potentials [160], Non-linear adsorption isotherms give rise to pre-waves (product adsorption) and post-waves (reactant adsorption), a phenomenon which was first discussed by Brdidka at the DME and since then by many authors [161, 162]. At the RDE,... 

In comparison to the mesoporous materials, less research has been published on the functionalization of microporous materials by direct grafting (excluding various types of ion exchange). It has been stated that some of the newly modified mesoporous materials suffer from the adsorption of products and by-products onto the amorphous walls of the support structure.11031 Microporous zeolitic... 

Pre-wave — In DC polarography, this is a part of the response of fast and reversible electrode reaction (- reversibility) complicated by the -+ adsorption of product on the - dropping mercury electrode surface Ox + ne (Red)ads Red, assuming that the reactant... 

If both the reactant and product are adsorbed on the electrode surface, the pre-wave appears if the adsorption of product is stronger than the adsorption of reactant, while the post-wave appears in the opposite case. If the adsorptions of both the reactant and product are equally strong, only a main wave can appear, but this is a simplification which neglects possible interactions between molecules in the first and second adsorbed layers. 

Due to adsorption of products on the electrode at this high concentration, the potential measurements at these sweep rates were not meaningful... 

Subscript p refers to adsorption of product. "Sediment is 95% water. 

Unsaturated carbenium ions are not formed by the adsorption of product olefins on pristine acid sites nor are they formed by the addition of olefins to saturated carbenium ions. Both are minor processes which form saturated carbenium ions and play a part only at higher conversions in the chain mechanism of cracking. Rather, they must be formed by aberrant side-reactions of the main conversion processes, reactions by which normal, saturated carbenium ions generate sitepoisoning unsaturated carbenium ions. 

Pre-adsorbed chloride reduced the amount of adsorbed ethylene and enhanced the adsorption of products.Assuming that chloride also reduces the surface concentration of atomic oxygen, then catalyst selectivity will rise since the partial oxidation reaction is first order on surface species while the complete oxidation is second order. 

Absorption and adsorption of product constituents, e.g. certain preservatives. 

Fio. 27. Gas-solid-solid trickle flow reactor concept for in situ adsorption of product. 

By calculating the heats of adsorption of products it is possible to obtain the activation energies for these reactions under conditions ruling out inhibition by products. Then 2 acr = 20 1 kcal/mole, and 2 co, = 26 1 kcal/mole, and this is in agreement with results obtained by other workers. 

A recent study by Kyriacou and Anagnostopolous [35] has shown that preparation of the electrode surface is also important. The current efficiency of smooth copper electrodes was found to diminish rapidly. This was probably due to adsorption of products and intermediates. Surface roughening (by anodisation) or thermal pretreatment of the electrode lead to changes in adsorption behaviour and extended the life of the electrode significantly. It is thought that these changes are a result of... 

In the reviews by both Skupinska, and Al-Jarallah et ai, it is suggested that the activities and selectivities of the catalysts are affected by strong adsorption of products, by isomerization or by a tendency to copolymerize into branched products. 

In order to show this behavior, let us return to the example treated in the preceding section two reactants Ai and A2 reacting in parallel on a catalyst with a common reactant B which will be assumed to be missing from the rate expressions. These are for the case of saturation of the surface and negligible adsorption of products ... 

Figure 22.15 presents the comparison between gas-flowing solids-fixed bed reactor E= 10) and the one without the adsorption of product E = 0). Both reactors operate isothermally, but with two cases presented, one for 500 K and the other for 540 K. From Figure 22.15, it can be seen that at low conversions, there is no big distinction in performance of different reactors. In contrast, a great improvement was found for gas-flowing solids-fixed bed reactor in and above the zone of equilibrium conversions. A comparison of the gas-flowing solids-fixed bed reactors E = 10) at two... 

The electrochemical reduction of NAD+ in aqueous solutions is well documented including studies on the adsorption of product, intermediates, and NAD" " itself on electrode surfaces [75, 97, 118, 124, 125, 395, 396]. In an initial polarographic study by Kaye and Stonehill [397], the reduction of NAD" " at the mercury electrode was observed as a single wave with an E j2 of Ri —0.9 V in neutral aqueous solution. Burnett and Underwood [118] resolved this single wave into two cathodic waves, a first one at 1/2 —1.1 V and a second at 1/2 -1.7 V, by recording... 

In this example, the only case where Etme is measured is that of the Rideal-Eley mechanism in part (b ) involving strong adsorption of reactant A and weak adsorption of product C. 

The Langmuir-Hinshelwood (LH) mechanism assumes that both A and B are adsorbed, and that the surface reaction of both adsorbed species is the ratedetermining step, which leads to the following equation for the initial reaction rate if adsorption of products is negligible ... 

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