Sequential adsorption-reaction

On co-adsorbing phenol and methanol, the protonation of methanol occurs on the active acid sites as the labile protons released from the phenol reacted with methanol. Thus protonated methanol became electrophilic methyl species, which undergo electrophilic substitution. The ortho position of phenol, which is close to the catalyst surface, has eventually become the substitution reaction center to form the ortho methylated products (Figure 3). This mechanism was also supported by the competitive adsorption of reactants with acidity probe pyridine [79]. A sequential adsorption of phenol and pyridine has shown the formation of phenolate anion and pyridinium ion that indicated the protonation of pyridine. 

In a system devised to oxidize a dye, glucose oxidase and horseradish peroxidase were coassembled by layer-by-layer alternative adsorption to construct multienzyme films. The peroxidase was adsorbed to poly(styrene sulfonate) while glucose oxidase was adsorbed to poly(ethylene imine), allowing for sequential redox reactions to take place resulting in the subsequent oxidation of the textile dye DA67 [71]. 

The temperature programmed desorption profile for the adsorption of butadiene in place of cis-2-butene is shown in Fig. 1, curve c. Two sets of products are observed. The product below 210°C is unreacted butadiene, and the products above 210°C are carbon dioxide and water. The similarity in the evolution of the combustion products of butene and butadiene is an indication that their combustion proceeds via similar reaction mechanisms. The similarity in the desorption of butadiene suggests that in butene adsorption, butadiene desorption is desorption limited. Indeed, that both butene and butadiene adsorb on the same type of sites has been confirmed by sequential adsorption experiments. The results are shown in Table III. It was found that if the C4 hydrocarbons are adsorbed sequentially without thermal desorption between adsorptions, the amounts of the final desorption products are the same as those in experiments where only the first hydrocarbon... 

When a reaction rate is measured in a chemical reactor, the reaction is generally a composite reaction comprised of a sequence of elementary reactions. An elementary reaction is a reaction that occurs at the molecular level exactly as written (Laidler, 1987). The mechanism of the reaction is the sequence of elementary reactions that comprise the overall or composite reaction. For example, mineral dissolution reactions generally include transport of reactant to the surface, adsorption of reactant, surface dilfusion of the adsorbate, reaction of the surface complex and release into solution, and transport of product species away from the surface. These reactions occur as sequential steps. Reaction of surface complexes and release to solution may happen simultaneously at many sites on a surface, and each site can react at a different rate depending upon its free energy (e.g., Schott et al., 1989). Simultaneous reactions occurring at different rates are known as parallel reactions. In a series of sequential reactions, the ratedetermining step is the step which occurs most slowly at the onset of the reaction, whereas for parallel steps, the rate-determining step is the fastest reaction. 

Reaction Vessels Assembled by the Sequential Adsorption of Polymers... 

This technique provides an opportunity to examine the "adsorption" and "reaction" steps sequentially at reaction temperatures and pressures. How sharply the individual steps can be separated depends largely upon the magnitude of the differences in rates and upon the data resolution capability of the experimental apparatus. Interpretation of the transient rapid response measurements in terms of steady state operation is needed if these results are to be most useful. Recent studies in this laboratory indicate that this approach holds some promise and it is the purpose of this paper to describe the adsorber-reactor system and its performance capabilities. The most recent design provides rapid gas-solid contact in a constant volume cell with transient rates for temperature and pressure measurements in the millisecond region. 

The activation of C-H bond in methane is a crucial hrst step in its combustion for power and heat generation. Once the hrst bond has been broken, sequential oxidation reactions to CO2 and H2O are relatively easy. A basic understanding of the activation of C-H bonds in methane is of vital importance since it permits one to assess the inhuence of catalytic and process parameters on the rate and efficiency of its catalytic combustion [29]. Several types of catalysts — including nonreducible oxides, reducible oxides, and metals — are capable of oxidizing methane with varying efficiencies. It is harder for C-H bonds to be activated in methane than in other hydrocarbons, due to the weaker adsorption of methane on oxides or on oxidized metal surfaces [30]. Strong adsorption of a saturated hydrocarbon is a prerequisite for combustion, but factors other than the strength of the C-H bond also affect the rate of combustion. 

The reaction sequence of formaldehyde formation and subsequent COad formation can proceed either as sequential reactions of adsorbed species, or it can involve formation and desorption of formaldehyde into the electrol5d e and subsequent re-adsorption and further decomposition of formaldehyde to COad. Considering the significant transport and catalyst loading effects discussed above, it is clear that desorption and subsequent re-adsorption plus dehydrogenation of formaldehyde will play an important role also for COad formation, although a direct reaction of adsorbed RIad species can not be ruled out. 

An approximate analysis of polymer adsorption as a set of sequential reactions leads to a simple equation for the adsorption isotherm expressed in terms of three parameters. Comparison of the model with recently published statistical theories reveals remarkable agreement in both the general shape of the isotherms and the predicted effects of molecular weight. The problems of applying such models to experimental data are discussed. 

Successive Ionic Layer Adsorption and Reaction (SILAR) and Related Sequential Solution-Phase Deposition Techniques... 

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