Advances in Catalysis and Related Subjects, Volume 8 by W G Frankenberg

By W G Frankenberg

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We shall deal first with these two serious setbacks (3). ADSORPTION PHENOMENA 23 2. The Structure of a Smooth Surface of an Adsorbent Usually in theoretical calculations of adsorption energies the surface of the adsorbent is idealized as if it were obtained by cutting a crystal into two halves with an ideally sharp razor blade. It is then generally assumed t ha t the atoms (or ions) of these freshly created surfaces do not alter their positions. From specular reflection experiments with molecular beams of hydrogen or helium ( 4 ) it may be concluded that cleavage surfaces of LiF or NaCl are very smooth surfaces indeed, the inequalities being caused only by the temperature movement and amounting to the order of magnitude of cm.

El turns out to be positive instead of negative. This part, therefore, re- 32 J. H. DE BOER sults in a repulsion instead of an attraction. 5 and re is the radius of a sphere in the metal containing one conduction electron. We shall use this expression in estimating the nonpolar van der Waals’ interaction energy of physically adsorbed atoms or molecules on metals and on charcoal. We see that also in this expression the potential energy is inversely proportional to the third power of the distance.

E q u a h n (26) could then be used t o calculate the contribution t o the adsorption energy due t o this polarization. It is not necessary to calculate F , however, as E, is immediately given by Some figures obtained in this way for gases adsorbed on charcoal are given in Table I. 1 It is clear that this effect leads t o a rather important contribution t o the adsorption energy, if not t o the most important, in those cases of adsorption of gases on conducting surfaces where no chemical interaction results.

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