Surface polarizability

De Boer and coworkers ° °" parameterized the shell model for silica polymorphs on the results of ab initio calculations of the potential energy surfaces, polarizabilities, and dipole moments of Si(OH)4 and (0H)3Si-0(H)-Si(OH)3 clusters. The structural characteristics and elastic moduli calculated with this set of parameters for three structures compared well with results computed with the use of both the rigid ion and the empirical shell models. ... 

The surface polarizability decreases with increasing modifer coverage as the surface region transforms from metal to metal compound. 

The yariation in catalytic function with increasing oxygen coyerage is in excellent agreement with surface characterization by molybdenum core leyel shifts and surface polarizability measurements. Clearly the physical measurements were performed on the actual catalytically actiye sites, and the nature of the actiye sites has been established. The catalytic results combined with the spectroscopic data also serve to calibrate the minimum molybdenum oxidation state required for acid catalyzed C-C bond breaking and formation of a secondary carbenium ion, namely. Mo(IV). 

Trasatti [28] has noticed that in aqueous solutions the Helmholtz capacity Ch of the simple sp metals, taken at the pzc, correlates with their electronic densities (see Fig. 5). This indicates that the surface polarizability of simple metals increases with their electronic densities, a trend that can be explained by the jellium model presented below. 

Fig. 40. Surface area-normalized turnover frequency for glyceryl tribut5Tate conversion as a function of surface polarizability. Reproduced from Ref. (369).

Figure 6.14 (Top) Fresh NanoMgO TEM images showing weii-defined 3-nm cubic- (100) oriented MgO nanocrystalhtes in an amorphous matrix. Foiiowing 500°C annealing these are converted into 13 nm wide defective cry statutes exposing (110) facets (Bottom) Relationship between MgO nanocrystal particle size and surface polarizability (AEk) and Auger parameter and XPS analysis, along with correlation of polarizabilty (A ) with activity for transesterification.

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