Adsorption experimental procedures

In considering the differential energy of adsorption, it is useful to picture an experimental procedure which allows the adsorption to proceed at constant temperature and in infinitely small stages. Then... 

Mercury porosimetry is generally regarded as the best method available for the routine determination of pore size in the macropore and upper mesopore range. The apparatus is relatively simple in principle (though not inexpensive) and the experimental procedure is less demanding than gas adsorption measurements, in either time or skill. Perhaps on account of the simplicity of the method there is some temptation to overlook the assumptions, often tacit, that are involved, and also the potential sources of error. 

A vast amount of research has been undertaken on adsorption phenomena and the nature of solid surfaces over the fifteen years since the first edition was published, but for the most part this work has resulted in the refinement of existing theoretical principles and experimental procedures rather than in the formulation of entirely new concepts. In spite of the acknowledged weakness of its theoretical foundations, the Brunauer-Emmett-Teller (BET) method still remains the most widely used procedure for the determination of surface area similarly, methods based on the Kelvin equation are still generally applied for the computation of mesopore size distribution from gas adsorption data. However, the more recent studies, especially those carried out on well defined surfaces, have led to a clearer understanding of the scope and limitations of these methods furthermore, the growing awareness of the importance of molecular sieve carbons and zeolites has generated considerable interest in the properties of microporous solids and the mechanism of micropore filling. 

The study of acid-base interaction is an important branch of interfacial science. These interactions are widely exploited in several practical applications such as adhesion and adsorption processes. Most of the current studies in this area are based on calorimetric studies or wetting measurements or peel test measurements. While these studies have been instrumental in the understanding of these interfacial interactions, to a certain extent the interpretation of the results of these studies has been largely empirical. The recent advances in the theory and experiments of contact mechanics could be potentially employed to better understand and measure the molecular level acid-base interactions. One of the following two experimental procedures could be utilized (1) Polymers with different levels of acidic and basic chemical constitution can be coated on to elastomeric caps, as described in Section 4.2.1, and the adhesion between these layers can be measured using the JKR technique and Eqs. 11 or 30 as appropriate. For example, poly(p-amino styrene) and poly(p-hydroxy carbonyl styrene) can be coated on to PDMS-ox, and be used as acidic and basic surfaces, respectively, to study the acid-base interactions. (2) Another approach is to graft acidic or basic macromers onto a weakly crosslinked polyisoprene or polybutadiene elastomeric networks, and use these elastomeric networks in the JKR studies as described in Section 4.2.1. 

After adsorption of CO and solution exchange with pure base electrolyte, the oxidation of adsorbed CO during a triangular potential scan is observed (see Fig. 1.4a). In a second run after adsorption of CO the electrode is emersed and transferred to the UHV chamber in the same way as in the normal experimental procedure. The electrode is then transferred back to the cell and re-immersed in the base electrolyte. A potential scan is applied to oxidize the adsorbate. Fig. 1,4b shows... 

Fig. 4.3. Cyclic voltammogram for adsorbed tin on platinum, v = 10 mV/s. Experimental procedure 11 min. adsorption from a 4 x 10-4 M Sn(S04)2 solution in 0.5 M H2S04 at 0.5 V followed by electrolyte replacement with pure supporting electrolyte.

Adsorption is determined by the depletion method using a Dohrmann DC 80 carbon analyzer. The mineral is contacted with the polymer solution and agitated with a mechanical tumbler for 24 hours, a time which has been verified to be sufficient for adsorption to be complete (9). A more detailed description of experimental procedures is given elsewhere (10). All the data reported in this study are taken in the plateau region of the adsorption isotherm. 

The scatter of points in Figure 1, with the value of k 3 ranging from 0.03 to 0.05, may reflect the more random behavior of coprecipitation by adsorption/trapping as compared to the more reproducible behavior of lattice substitution. Sensitivity of the partition coefficient to experimental conditions is, in fact, one of the tests for distinguishing the former from the latter (21,34). Attempts to refine the experimental procedure to achieve greater consistency therefore are not warranted any resultant more precise value of the partition coefficient would be applicable only to a more limited set of conditions. 

Describe an experimental procedure for determining adsorption isotherms. 

In this section will be described the experimental procedures which measure the rate of adsorption and the sticking probability the experimental results will be given and will be interpreted in terms of an energy-level diagram and an activation energy and finally the bearing of these results on catalysis will be discussed. 

This method has considerable advantages over the free boundary methods with regard to experimental procedure. Possible objections to the method are (a) the calibration of the cell with material of different relative molecular mass and/or shape from the material under investigation is not necessarily valid and (b) entrapment of air bubbles in the pores or adsorption of the diffusing molecules on the pore walls will invalidate the results. 

Acetaldehyde decomposition, reaction pathway control, 14-15 Acetylene, continuous catalytic conversion over metal-modified shape-selective zeolite catalyst, 355-370 Acid-catalyzed shape selectivity in zeolites primary shape selectivity, 209-211 secondary shape selectivity, 211-213 Acid molecular sieves, reactions of m-diisopropylbenzene, 222-230 Activation of C-H, C-C, and C-0 bonds of oxygenates on Rh(l 11) bond-activation sequences, 350-353 divergence of alcohol and aldehyde decarbonylation pathways, 347-351 experimental procedure, 347 Additives, selectivity, 7,8r Adsorption of benzene on NaX and NaY zeolites, homogeneous, See Homogeneous adsorption of benzene on NaX and NaY zeolites... 

In any investigation of the energetics of adsorption, a choice has to be made of whether to determine the differential or the corresponding integral molar quantities of adsorption. The decision will affect all aspects of the work including the experimental procedure and the processing and interpretation of the data. 

Our aim in this section is to outline the advantages and limitations of the main experimental procedures now available for the determination of the differential enthalpies of adsorption. Both thermodynamic and practical aspects are summarized here, but the latter are discussed in more detail in Chapters 3 and 5. 

Because of the appreciable enhancement of the adsorption potential in micropores of a few molecular diameters in width (see Section 1.7 and Figure 1.6), microcalorimetry can provide a useful means of assessing microporosity. The available experimental procedures are outlined in the following sections. 

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