Minimum Bronsted acidity

Whereas the proton (H ) can be considered the ultimate Bronsted acid (having no electron), the helium dication (He ) is an even stronger, doubly electron-deficient eleetron aceeptor. In a theoretical, calculational study we found that the helionitronium trication (NOaHe" ) has a minimum structure isoelectronic and isostructural... 

The various support materials have different effects on potential carbon formation. This seems to go in parallel with the Lewis/Bronsted acidity. The main commercially used catalyst supports can be ranked as follows in decreasing order of carbon forming tendency (and thus in decreasing order of the important minimum practical steam/ carbon ratio) a-alumina > magnesium aluminate (spinel) > calcium aluminate > alkalized calcium aluminate [419],... 

In a typical high-Al Y zeolite, each Si is joined (via -0- bonds) to four A1 atoms, i.e., each A1 has three next-to-nearest neighbors (NNN). If each A1 is associated with a H, such a zeolite contains the maximum number of Bronsted acid sites, but the minimum (average)... 

Another method is to measure the amount of a gaseous base, such as ammonia, pyridine, or quinoline, adsorbed at elevated temperatures under a specified set of conditions. This has the advantage of allowing the study of a catalyst under conditions more nearly similar to those of reaction. Ammonia has been used extensively. Catalysts may be compared in terms of the amount of ammonia adsorbed as a function of the temperature over a range such as ISO to SOO C. A minimum temperature of about 150 C is necessary to eliminate physical adsorption. By infrared spectra it is possible to distinguish between Bronsted and Lewis acid sites. More details on characterizing the acidity of solid catalysts are described in reviews by Formi (1974), and by Bensei and Winquist (1978). 

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