Adsorption catalytic activity and

Pines and Haag studied the correlation between trimethylamine adsorption and catalytic activities of aluminas for isomerization and dehydration (36). From the results obtained they reached the following general conclusions (a) there is a satisfactory correlation between catalytic activity and amine chemisorption values for aluminas obtained from the same methods of preparation—both measure acidity (6) there is no satisfactory correlation between catalytic activity and amine index of aluminas obtained from different sources. 

VIII. Factors Affecting the Adsorptivity and Catalytic Activity of a Semiconductor 241... 

The fifth consequence of the theory is that the adsorptivity and catalytic activity of a semiconductor are affected by illumination. When a crystal absorbs light waves of photoelectrically active frequencies (i.e., frequencies exciting the internal photoeffect), this leads, generally speaking, to a change... 

In conclusion we stress once more that the above-considered mechanism of the effect of illumination on the adsorptivity and catalytic activity of a semiconductor holds in the case when the absorption of light increases the number of free electrons or holes (or both) in the crystal. This, however, does not always take place. The absorption of light by the crystal may proceed by an exciton mechanism. This seems to be the case in the region of intrinsic absorption, which is as a rule photoelectrically inactive. 

Let us consider the sixth consequence of the theory—the effect of an external electric field applied to a semiconductor on its adsorptivity and catalytic activity. 

This effect predicted by the theory (effect of an external electric field on the adsorptivity and catalytic activity of a semiconductor) has not been... 

Now consider another effect which also follows from the theory. This is the dependence of the specific (per unit surface) adsorptivity and catalytic activity on the dimensions of the sample, i.e., on the degree of disperseness of the catalyst. 

Illumination of the semiconductor by photoelectrically active light leads to a change in its adsorptivity and catalytic activity (Sec. VIII,A). This is because illumination causes a change in the surface concentrations of the electron and hole gases. This leads to a change in the relative content of the different forms of chemisorption and, consequently, in the reactivity of the chemisorbed particles. 

At suflSciently high dispersion of the semiconductor, its adsorptivity and catalytic activity are sensitive to the degree of dispersion (Sec. VIII,B). This is because, in the case of sufiiciently small crystals, the position of the Fermi level depends on the dimensions of the crystal. 

Reduction of N2O was used as model electrocatalytic reaction on well-defined surfaces [102, 103]. Pt(lll) and Pt(lOO) electrodes covered with Rh adlayers were prepared for these studies. It was shown that the adsorptive and catalytic activity of the adlayers differs from those of the bulk single-crystal electrodes. 

Besides adsorption of analytes, active sites on the supporting surface and in the stationary phase can trigger catalytic decomposition of unstable analytes such as trimethylsilyl derivatives (47). A further source of adsorptive and catalytic activities are the residues of additives often used to deactivate the surface and to catalyze the immobilization of the stationary phase. 

These observations show that in catalytic experiments in which the temperature approaches one third of the melting point, the presence of an adsorbate may alter the surface planes of catalyst crystallites and thus alter the adsorption and catalytic activity. If the particles are very small, such effects may occur at even lower temperatures. 

The lack of correlation between isosteric heats of adsorption and catalytic activity illustrates the point we have been stressing the strength of attachment of a base to a catalyst surface is not a valid index of catalytic activity when a substantial portion of the base is strongly bonded to inactive portions of a catalyst surface. Putting it more explicitly, isosteric heats of adsorption are useful indexes for the prediction of acid-catalyzed... 

Ethers. The polycondensation of diphenyl ether and furfural (1 1.5mole ratio) in presence of sulfuric acid yields a resin which has been sulfonated by sulfuric acid at 50 °C for 10 h to give a cation-exchange resin The swelling and the exchange capacity of the product increase with the amount of sulfuric acid present during the polycondensation and are higher for a resin obtained by polycondensation in carbon tetrachloride than the one prepared in absence of solvent. The thermal stability of sulfonated diphenyl ether-furfural resin is more than that of KU-1 and comparable to that of KU-2. The sulfonic acid resin derived from the copolymer obtained by the polymerization of diphenyl ether and furfural at a mole ratio of 1 2 in carbon tetrachloride has optimum adsorption and catalytic activity... 

Winter 10) relates isotopic exchange of molecular oxygen with magnesium oxide, zinc oxide, chromium oxide, nickel oxide, and iron oxide. He also compares the rates of isotopic exchange of these oxides with oxygen and the rates of adsorption and catalytic activity relating to the oxidation of CO and the decomposition of NgO. 

The electrical conductivity of the solid would also vary as a function, of the impurity nature and the chemical effect of these must be different. However, experimental results show that the relationship between conductivity and catalytic activity is much more complex. This is probably due to the fact that the conductivity of polycrystalline semiconductors often is not affected by changes in the Fermi level of the surface. Thus there must be another connection between changes in electron work functions of modified catalysts and their adsorptive and catalytic activities. 

Good columns eventually deteriorate over time due to modification of the stationary phase film or glass surface induced by moisture or matrix components introduced with the samples or by the carrier gas, thermal stress, attack by oxygen and aging. Column efficiency for inert compounds may remain acceptable but increasing adsorptive and catalytic activity eventually precludes the separation of polar compounds. Figure 2.16 shows an example of the influence of column deterioration on the separation of several... 

Zeolites are used as detergent builders, adsorbents, and catalysts. In the past decade, we saw the development of a variety of zeoiite membranes, and a number of investigators reported on the preparation of such membranes and their applications to a variety of separation systems. These research activities are motivated by features common to inorganic membranes, such as thermal resistance and resistance to organic solvents, and features unique to zeolite materials, such as molecular sieving, selective adsorption, and catalytic activity.In this article, the discussion will be restricted to zeolite membranes for use in separation and catalysis. First, an overview is presented on recent progress in zeolite membranes, followed by a discussion of our research activities. 

Capability of B-N-Fe composition samples to remove oxalic acid (OA) from water was investigated [24] and it was established (Table 7.5) that sorption of OA depends on surface and porosity properties of the material used and does not exceed 40%. H2C2O4 decomposition degree under UV in presence of each sample is rather high (80-90%). Addition of HgOg (photo-Fenton system) does not affect the catalytic activity of composites. Adsorption and catalytic activity of materials were investigated used by XRD and IR methods. Formation of photoactive ferric-oxalate complexes explains efficiency of catalytic systems (Equations 7.11-7.15). 

The magnitude of adsorption heat corresponds to the strength of adsorption bond, and so there should also be some relationship between adsorption and catalytic activity. The catal3dic activity is reversely proportional to adsorption strength when the surface coverage of reaction molecule reaches certain level, as indicated by Sabatier s theory of intermediate complex and experience. On the other hand, if adsorption is too weak, it is difficult to activate adsorbed molecules. The best activity can be obtained only in the case with suitable adsorption strength. This relationship is usually called as a volcano type curve, as shown in Fig. 2.4. 

---