Zeolites Sanderson electronegativity

Figure 2. (A) v(OH) ( ) and the v(=CH) ( ) wavenumbers of MBOH adsorbed on zeolites as a function of Sanderson electronegativity (B) Intensity of v(OH) band created by dissociated H2S as a function of Sanderson electronegativity...

Pyrrole has also been applied as a probe molecule in FTIR specroscopic studies. Upon interaction with a base site, the N—H stretching vibration is found to shift to lower wavenumber and in alkali metal-exchanged zeolites this behavior has been found to correlate with both N Is XPS data and the negative charge calculated from Sanderson electronegativities [4, 26]. 

Fig. 32. H NMR shifts, 6n, of bridging OH groups in the supercages and channels of aluminosilicate type zeolites as a function of the mean Sanderson electronegativity Sm [222] given in columns 5 and 6 of Table 5 and in [220]...

A detailed infrared study of pyrrole adsorption on a series of zeolites saturated with alkaline cations shows that the Avnh increase depends on two parameters, a high A1 content and a low electronegativity of the cation i.e. Cs rather than Li (62,66,67). The experimental Avnh values in figure 10 show a good relationship with the mean charge on the framework oxygen calculated from Sanderson electronegativity (62,67). 

Figure 11. Change in binding energy of O (Is) (from XPS) in various zeolites as a function of the average oxygen charge calculated from Sanderson electronegativity (from (104))...

The effect of chemical composition of a zeolite on its average Bronsted acidity, can be accounted for by its average Sanderson electronegativity, allowing... 

Ferino et al. [242], exploring the reaction of2-methylfuran to 2-methylthio-phene on Me-Y zeolites (Me = Li, Na, K, Rb, Cs), proposed ionic and radical reaction pathways. The ratio of these two pathways was found to be directly correlated to the partial charge on the oxygen as calculated by the Sanderson electronegativity equaUzation principle. The selectivity to form 2-methylthiophene increased in the order Li,Na-Y < Na-Y < K,Na-Y < Rb,Na-Y = Cs,Na-Y, which is in Hne with the increasing basicity of these zeolites. As the catalytic activity exhibited a rather complex behavior due to the contribution of the two reaction pathways, more work seems necessary to allow use of this reaction on a broader basis. 

One of the parameters in the broad class of liquid adsorption mechanisms is the interaction between the acidic and basic sites of the adsorbent and the adsorbate. The acidity of zeolitic adsorbent is normally affected by the zeolite Si02/Al203 molar ratio, the ionic radii and the valence of the cations exchanged into the zeolite. In this contribution, Sanderson s model of intermediate electronegativity of zeolitic adsorbent acidity (SjJ can be calculated as a representation of the strength of the adsorbent acidity based on the following equation ... 

Microcrystalline solids such as zeolites and zeolite like structures have shown the utility of those properties in the domain of acid catalysis. However, little is known on their possibilities as base catalysts. It has been shown [ref. 1,2] that zeolites have basic sites which are able to catalyze reactions needing weak and medium basic strengths. Moreover, a correlation between the basicity and the Sanderson s average electronegativity Df the framework has been observed [ref. 3], Then, their activity as base catalysts can be modified by changing the countercation [ref. 4], the framework Si/Al ratio, or by introducing atoms other than Si and Al in the framework [ref. 5],... 

Recently Jacobs (84, 85) has proposed another system of structural hydroxyls in zeolites based on the mean electronegativities of zeolite lattices according to Sanderson. It was concluded as well that the Bronsted acidity of zeolites varies continuously with their Si/Al content. Let us compare these two approaches. 

Researchers attempted to find correlations between the composition of the unit cell and the selectivity for paraxylene. In this respect, D. Barthomeuf (9) proposed an approach based on Sanderson s intermediate electronegativity which allows us to estimate the basicity of zeolite oxygens, and hence the strength of the acid-base interaction between xylene molecules and zeolites. It should be noted that these calculations provide an insight into the interactions between the zeolite structure and the molecules at low loading only, i.e. when the interactions between adsorbed molecules are negligible. 

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